The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Michael A. Gray - One of the best experts on this subject based on the ideXlab platform.
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A Voltage-Dependent Ca^2+ Influx Pathway Regulates the Ca^2+-Dependent Cl^− Conductance of Renal IMCD-3 Cells
Journal of Membrane Biology, 2009Co-Authors: John E. Linley, S. H. Boese, Nicholas L. Simmons, Michael A. GrayAbstract:We have previously shown that the membrane conductance of mIMCD-3 cells at a holding potential of 0 mV is dominated by a Ca^2+-dependent Cl^− current (I_CLCA). Here we report that I_CLCA activity is also voltage dependent and that this dependence on voltage is linked to the opening of a novel Al^3+-sensitive, voltage-dependent, Ca^2+ influx pathway. Using whole-cell patch-clamp recordings at a physiological holding potential (−60 mV), I_CLCA was found to be inactive and resting currents were predominantly K^+ selective. However, membrane depolarization to 0 mV resulted in a slow, sigmoidal, activation of I_CLCA ( T _0.5 ~ 500 s), while Repolarization in turn resulted in a monoexponential decay in I_CLCA ( T _0.5 ~ 100 s). The activation of I_CLCA by depolarization was reduced by lowering extracellular Ca^2+ and completely inhibited by buffering cytosolic Ca^2+ with EGTA, suggesting a role for Ca^2+ influx in the activation of I_CLCA. However, raising bulk cytosolic Ca^2+ at −60 mV did not produce sustained I_CLCA activity. Therefore I_CLCA is dependent on both an increase in intracellular Ca^2+ and depolarization to be active. We further show that membrane depolarization is coupled to opening of a Ca^2+ influx pathway that displays equal permeability to Ca^2+ and Ba^2+ ions and that is blocked by extracellular Al^3+ and La^3+. Furthermore, Al^3+ completely and reversibly inhibited depolarization-induced activation of I_CLCA, thereby directly linking Ca^2+ influx to activation of I_CLCA. We speculate that during sustained membrane depolarization, calcium influx activates I_CLCA which functions to modulate NaCl transport across the apical membrane of IMCD cells.
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A voltage-dependent Ca2+ influx pathway regulates the Ca 2+-dependent Cl- conductance of renal IMCD-3 cells
Journal of Membrane Biology, 2009Co-Authors: John E. Linley, S. H. Boese, Nicholas L. Simmons, Michael A. GrayAbstract:We have previously shown that the membrane conductance of mIMCD-3 cells at a holding potential of 0 mV is dominated by a Ca2+-dependent Cl(-) current (I(CLCA)). Here we report that I(CLCA) activity is also voltage dependent and that this dependence on voltage is linked to the opening of a novel Al3+-sensitive, voltage-dependent, Ca2+ influx pathway. Using whole-cell patch-clamp recordings at a physiological holding potential (-60 mV), ICLCA was found to be inactive and resting currents were predominantly K+ selective. However, membrane depolarization to 0 mV resulted in a slow, sigmoidal, activation of ICLCA (T(0.5) approximately 500 s), while Repolarization in turn resulted in a monoexponential decay in I(CLCA) (T (0.5) approximately 100 s). The activation of I(CLCA) by depolarization was reduced by lowering extracellular Ca2+ and completely inhibited by buffering cytosolic Ca2+ with EGTA, suggesting a role for Ca2+ influx in the activation of I(CLCA). However, raising bulk cytosolic Ca2+ at -60 mV did not produce sustained I(CLCA) activity. Therefore I(CLCA) is dependent on both an increase in intracellular Ca2+ and depolarization to be active. We further show that membrane depolarization is coupled to opening of a Ca2+ influx pathway that displays equal permeability to Ca2+ and Ba2+ ions and that is blocked by extracellular Al3+ and La3+. Furthermore, Al3+ completely and reversibly inhibited depolarization-induced activation of ICLCA, thereby directly linking Ca2+ influx to activation of I(CLCA). We speculate that during sustained membrane depolarization, calcium influx activates ICLCA which functions to modulate NaCl transport across the apical membrane of IMCD cells.
John E. Linley - One of the best experts on this subject based on the ideXlab platform.
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A Voltage-Dependent Ca^2+ Influx Pathway Regulates the Ca^2+-Dependent Cl^− Conductance of Renal IMCD-3 Cells
Journal of Membrane Biology, 2009Co-Authors: John E. Linley, S. H. Boese, Nicholas L. Simmons, Michael A. GrayAbstract:We have previously shown that the membrane conductance of mIMCD-3 cells at a holding potential of 0 mV is dominated by a Ca^2+-dependent Cl^− current (I_CLCA). Here we report that I_CLCA activity is also voltage dependent and that this dependence on voltage is linked to the opening of a novel Al^3+-sensitive, voltage-dependent, Ca^2+ influx pathway. Using whole-cell patch-clamp recordings at a physiological holding potential (−60 mV), I_CLCA was found to be inactive and resting currents were predominantly K^+ selective. However, membrane depolarization to 0 mV resulted in a slow, sigmoidal, activation of I_CLCA ( T _0.5 ~ 500 s), while Repolarization in turn resulted in a monoexponential decay in I_CLCA ( T _0.5 ~ 100 s). The activation of I_CLCA by depolarization was reduced by lowering extracellular Ca^2+ and completely inhibited by buffering cytosolic Ca^2+ with EGTA, suggesting a role for Ca^2+ influx in the activation of I_CLCA. However, raising bulk cytosolic Ca^2+ at −60 mV did not produce sustained I_CLCA activity. Therefore I_CLCA is dependent on both an increase in intracellular Ca^2+ and depolarization to be active. We further show that membrane depolarization is coupled to opening of a Ca^2+ influx pathway that displays equal permeability to Ca^2+ and Ba^2+ ions and that is blocked by extracellular Al^3+ and La^3+. Furthermore, Al^3+ completely and reversibly inhibited depolarization-induced activation of I_CLCA, thereby directly linking Ca^2+ influx to activation of I_CLCA. We speculate that during sustained membrane depolarization, calcium influx activates I_CLCA which functions to modulate NaCl transport across the apical membrane of IMCD cells.
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A voltage-dependent Ca2+ influx pathway regulates the Ca 2+-dependent Cl- conductance of renal IMCD-3 cells
Journal of Membrane Biology, 2009Co-Authors: John E. Linley, S. H. Boese, Nicholas L. Simmons, Michael A. GrayAbstract:We have previously shown that the membrane conductance of mIMCD-3 cells at a holding potential of 0 mV is dominated by a Ca2+-dependent Cl(-) current (I(CLCA)). Here we report that I(CLCA) activity is also voltage dependent and that this dependence on voltage is linked to the opening of a novel Al3+-sensitive, voltage-dependent, Ca2+ influx pathway. Using whole-cell patch-clamp recordings at a physiological holding potential (-60 mV), ICLCA was found to be inactive and resting currents were predominantly K+ selective. However, membrane depolarization to 0 mV resulted in a slow, sigmoidal, activation of ICLCA (T(0.5) approximately 500 s), while Repolarization in turn resulted in a monoexponential decay in I(CLCA) (T (0.5) approximately 100 s). The activation of I(CLCA) by depolarization was reduced by lowering extracellular Ca2+ and completely inhibited by buffering cytosolic Ca2+ with EGTA, suggesting a role for Ca2+ influx in the activation of I(CLCA). However, raising bulk cytosolic Ca2+ at -60 mV did not produce sustained I(CLCA) activity. Therefore I(CLCA) is dependent on both an increase in intracellular Ca2+ and depolarization to be active. We further show that membrane depolarization is coupled to opening of a Ca2+ influx pathway that displays equal permeability to Ca2+ and Ba2+ ions and that is blocked by extracellular Al3+ and La3+. Furthermore, Al3+ completely and reversibly inhibited depolarization-induced activation of ICLCA, thereby directly linking Ca2+ influx to activation of I(CLCA). We speculate that during sustained membrane depolarization, calcium influx activates ICLCA which functions to modulate NaCl transport across the apical membrane of IMCD cells.
Richard L. Verrier - One of the best experts on this subject based on the ideXlab platform.
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crescendo in depolarization and Repolarization heterogeneity heralds development of ventricular tachycardia in hospitalized patients with decompensated heart failure
Circulation-arrhythmia and Electrophysiology, 2012Co-Authors: Bruce D. Nearing, Gregory A. Wellenius, Mark E. Josephson, Andrew J. Burger, Murray A. Mittleman, Richard L. VerrierAbstract:Background— A critical need exists for reliable warning markers of in-hospital life-threatening arrhythmias. We used a new quantitative method to track interlead heterogeneity of depolarization and Repolarization to detect premonitory changes before ventricular tachycardia (VT) in hospitalized patients with acute decompensated heart failure. Methods and Results— Ambulatory ECGs (leads V1, V5, and aVF) recorded before initiation of drug therapy from patients enrolled in the PRECEDENT (Prospective Randomized Evaluation of Cardiac Ectopy with Dobutamine or Nesiritide Therapy) trial were analyzed. R-wave heterogeneity (RWH) and T-wave heterogeneity (TWH) were assessed by second central moment analysis and T-wave alternans (TWA) by modified moving average analysis. Of 44 patients studied, 22 had experienced episodes of VT (≥4 beats at heart rates >100 beats/min) following ≥120 minutes of stable sinus rhythm, and 22 were age- and sex-matched patients without VT. TWA increased from 18.6±2.1 μV (baseline, mean±SEM) to 27.9±4.6 μV in lead V5 at 15 to 30 minutes before VT ( P <0.05) and remained elevated until the arrhythmia occurred. TWA results in leads V1 and aVF were similar. RWH and TWH were elevated from 164.1±33.1 and 134.5±20.6 μV (baseline) to 299.8±54.5 and 239.2±37.0 μV at 30 to 45 minutes before VT ( P <0.05), respectively, preceding the crescendo in TWA by 15 minutes. Matched patients without VT did not display elevated RWH (185.5±29.4 μV) or TWH (157.1±27.2 μV) during the 24-hour period. Conclusions— This investigation is the first clinical demonstration of the potential utility of tracking depolarization and Repolarization heterogeneity to detect crescendos in electrical instability that could forewarn of impending nonsustained VT. Clinical Trial Registration— URL: . Unique identifier: [NCT00270400][1]. [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT00270400&atom=%2Fcircae%2F5%2F1%2F84.atom
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Crescendo in depolarization and Repolarization heterogeneity heralds development of ventricular tachycardia in hospitalized patients with decompensated heart failure
Circulation: Arrhythmia and Electrophysiology, 2012Co-Authors: Bruce D. Nearing, Gregory A. Wellenius, Mark E. Josephson, Andrew J. Burger, Murray A. Mittleman, Richard L. VerrierAbstract:Background-A critical need exists for reliable warning markers of in-hospital life-threatening arrhythmias. We used a new quantitative method to track interlead heterogeneity of depolarization and Repolarization to detect premonitory changes before ventricular tachycardia (VT) in hospitalized patients with acute decompensated heart failure. Methods and Results-Ambulatory ECGs (leads V 1, V 5, and aVF) recorded before initiation of drug therapy from patients enrolled in the PRECEDENT (Prospective Randomized Evaluation of Cardiac Ectopy with Dobutamine or Nesiritide Therapy) trial were analyzed. R-wave heterogeneity (RWH) and T-wave heterogeneity (TWH) were assessed by second central moment analysis and T-wave alternans (TWA) by modified moving average analysis. Of 44 patients studied, 22 had experienced episodes of VT (?4 beats at heart rates >100 beats/min) following >120 minutes of stable sinus rhythm, and 22 were age- and sex-matched patients without VT. TWA increased from 18.6?2.1 ?V (baseline, mean?SEM) to 27.9?4.6 ?V in lead V5 at 15 to 30 minutes before VT (P
Charles Antzelevitch - One of the best experts on this subject based on the ideXlab platform.
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the early Repolarization pattern a consensus paper
Journal of the American College of Cardiology, 2015Co-Authors: Peter W Macfarlane, Charles Antzelevitch, Mark Potse, Frederic Sacher, Michel Haissaguerre, Heikki V Huikuri, Raphael Rosso, Jani T Tikkanen, Hein J J WellensAbstract:The term early Repolarization has been in use for more than 50 years. This electrocardiographic pattern was considered benign until 2008, when it was linked to sudden cardiac arrest due to idiopathic ventricular fibrillation. Much confusion over the definition of early Repolarization followed. Thus, the objective of this paper was to prepare an agreed definition to facilitate future research in this area. The different definitions of the early Repolarization pattern were reviewed to delineate the electrocardiographic measures to be used when defining this pattern. An agreed definition has been established, which requires the peak of an end-QRS notch and/or the onset of an end-QRS slur as a measure, denoted Jp, to be determined when an interpretation of early Repolarization is being considered. One condition for early Repolarization to be present is Jp ≥0.1 mV, while ST-segment elevation is not a required criterion.
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abnormal Repolarization as the basis for late potentials and fractionated electrograms recorded from epicardium in experimental models of brugada syndrome
Journal of the American College of Cardiology, 2014Co-Authors: Tamas Szel, Charles AntzelevitchAbstract:Objectives The aim of this study was to test the hypothesis that late potentials and fractionated electrogram activity are due to delayed depolarization within the anterior aspects of right ventricular (RV) epicardium in experimental models of Brugada syndrome (BrS). Background Clinical reports have demonstrated late potentials on signal-averaged electrocardiography (ECG) recorded in patients with BrS. Recent studies report the appearance of late potentials and fractionated activity on bipolar electrograms recorded in the epicardium of the RV outflow tract in patients with BrS. Methods Action potential and bipolar electrograms were recorded at epicardial and endocardial sites of coronary-perfused canine RV wedge preparations, together with a pseudo-ECG. The transient outward potassium current agonist NS5806 (5 μM) and the Ca 2+ -channel blocker verapamil (2 μM) were used to pharmacologically mimic the BrS genetic defect. Results Fractionated electrical activity was observed in RV epicardium, but not in endocardium, as a consequence of heterogeneities in the appearance of the second upstroke of the epicardial action potential, and discrete high-frequency spikes developed as a result of concealed phase 2 re-entry. In no case did we observe primary conduction delay as the cause of the BrS ECG phenotype or of late potential or fractionated electrogram activity. Quinidine (10 μM) and the phosphodiesterase-3 inhibitors cilostazol (10 μM) and milrinone (2.5 μM) restored electrical homogeneity, thus abolishing all late potentials and fractionated electrical activity. Conclusions These data point to an alternative pathophysiological basis for late potentials and fractionated electrical activity recorded in the right ventricle in the setting of BrS. We demonstrate an association of such activity with abnormal Repolarization and not with abnormal depolarization or structural abnormalities.
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Early Repolarization syndrome: A decade of progress
Journal of Electrocardiology, 2013Co-Authors: Ihor Gussak, Charles AntzelevitchAbstract:Stemming back to the days of Einthoven, ECG phenomena of “early ventricular Repolarization” were often misinterpreted or dismissed without appropriate clinical consideration or detailed investigation. This ensued because of a prevailing opinion that the nature of these phenomena was largely "benign". Early Repolarization changes consistent with Brugada Syndrome (BrS) were interpreted as "innocent" and therefore, overlooked for decades until 1992.1 The so-called "early Repolarization syndrome" (ERS) was universally and unequivocally regarded as "normal", a "normal variant", or a "benign early Repolarization" until 2000.2 A decade ago, we challenged the “benign” nature of ERS.2 The available experimental data suggested that:
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the pathophysiological mechanism underlying brugada syndrome depolarization versus Repolarization
Journal of Molecular and Cellular Cardiology, 2010Co-Authors: Arthur A M Wilde, Pieter G Postema, Jose M Di Diego, Sami Viskin, Hiroshi Morita, Jeffrey M Fish, Charles AntzelevitchAbstract:This Point/Counterpoint presents a scholarly debate of the mechanisms underlying the electrocardiographic and arrhythmic manifestations of Brugada syndrome (BrS), exploring in detail the available evidence in support of the Repolarization vs. depolarization hypothesis.
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does tpeak tend provide an index of transmural dispersion of Repolarization
Heart Rhythm, 2007Co-Authors: Charles Antzelevitch, Jose M Di Diego, Sami Viskin, Serge Sicouri, Alexander Burashnikov, Wataru Shimizu, Peter R Kowey, Li ZhangAbstract:Differences in the time course of Repolarization of the three predominant myocardial cell types have been shown to contribute to the inscription of the T wave of the electrocardiogram (ECG). Voltage gradients developing as a result of the different time course of Repolarization of phases 2 and 3 in the three cell types give rise to opposing voltage gradients on either side of the M region, which are in part responsible for the inscription of the T wave.1 In the case of an upright T wave, the epicardial response is the earliest to repolarize and the M cell action potential is the latest. In the coronary-perfused wedge preparation, Repolarization of the epicardial action potential coincides with the peak of the T wave and Repolarization of the M cells is coincident with the end of the T wave, so that the interval from the peak to the end of the T wave provides a measure of transmural dispersion of Repolarization (TDR). Based on these early studies, the Tpeak-Tend interval in precordial ECG leads was suggested to provide an index of transmural dispersion of Repolarization.2 More recent studies have also provided guidelines for the estimation of transmural dispersion of Repolarization in the case of more complex T waves, including negative, biphasic and triphasic T waves.3 In such cases, the interval from the nadir of the first component of the T wave to the end of the T wave was shown to provide an electrocardiographic approximation of TDR. While these relationships are relatively straight forward in the coronary-perfused wedge preparation, extrapolation to the surface ECG recorded in vivo must be approached with great caution and will require careful validation. The Tpeak-Tend interval is unlikely to provide an absolute measure of transmural dispersion in vivo, as elegantly demonstrated by Xia and coworkers4. However, changes in this parameter are thought to be capable of reflecting changes in spatial dispersion of Repolarization, particularly TDR, and thus may be prognostic of arrhythmic risk under a variety of conditions.5-10 Takenaka et al. recently demonstrated exercise-induced accentuation of the Tpeak-Tend interval in LQT1 patients, but not LQT2.9 These observations coupled with those of Schwartz et al.11, demonstrating an association between exercise and risk for TdP in LQT1, but not LQT2, patients, point to the potential value of Tpeak-Tend in forecasting risk for the development of Torsade de Pointes (TdP). Direct evidence in support of Tpeak-Tend as an index to predict TdP in patients with long QT syndrome (LQTS) was provided by Yamaguchi and co-workers.12 These authors concluded that Tpeak-Tend is more valuable than QTc and QT dispersion as a predictor of TdP in patients with acquired LQTS. Shimizu et al. demonstrated that Tpeak-Tend, but not QTc, predicted sudden cardiac death in patients with hypertrophic cardiomyopathy.8 In a case-controlled study comparing 30 cases of acquired bradyarrhythmias complicated by TdP and 113 cases with uncomplicated bradyarrhythmias, Topilski et al found that QT, QTc and Tpeak-Tend intervals were strong predictors of TdP, with the best single discriminator being a prolonged Tpeak-Tend. 13 Watanabe et al. demonstrated that prolonged Tpeak-Tend is associated with inducibility as well as spontaneous development of ventricular tachycardia (VT) in high risk patients with organic heart disease.10 These interesting studies demonstrating an association between an increase in Tpeak-Tend and arrhythmic risk notwithstanding, direct validation of Tpeak-Tend measured at the body surface as an index of TDR is still lacking. Guidelines for such validation have been suggested repeatedly.1, 3, 14 Because the precordial leads view the electrical field across the ventricular wall, Tpeak-Tend would be expected to be most representative of TDR in these leads. The precordial leads are unipolar leads placed on the chest that are referenced to Wilson central terminal. The direction of these leads is radially outward from the “center” of the heart, the center of the Einthoven triangle. Unlike the precordial leads, the bipolar limb leads, including leads I, II, and III, do not look across the ventricular wall. While Tpeak-Tend intervals measured in these limb leads may provide an index of TDR, they are more likely to reflect global dispersion, including apico-basal and interventricular dispersion of repoalrization.4, 15 A large increase in TDR is likely to be arrhythmogenic because the dispersion of Repolarization and refractoriness occurs over a very short distance (the width of the ventricular wall), creating a steep Repolarization gradient.16, 17 It is the steepness of the Repolarization gradient rather than the total magnitude of dispersion that determines its arrhythmogenic potential. Apico-basal or interventricular dispersion of Repolarization is less informative because it may or may not be associated with a steep Repolarization gradient and thus may or may not be associated with arrhythmic risk. The other critical point to consider is that TDR can be highly variable in different regions of the ventricular myocardium, particularly under pathophysiologic conditions. Consequently, it is important to measure Tpeak-Tend independently in each of the precordial leads and it is inadvisable to average Tpeak-Tend among several leads.4 Because LQTS is principally a left ventricular disorder, TDR is likely to be greatest in the left ventricular wall or septum and thus to be best reflected in left precordial leads or V3, respectively. Yamaguchi et al. in their study of acquired LQTS targeted lead V5.12 In contrast, because Brugada syndrome is a right ventricular disorder, TDR is greatest in the right ventricular free wall and thus is best reflected in the right precordial leads. For this reason, Castro et al. targeted lead V2 in their study.18 The criteria for validation of Tpeak-Tend as an index of TDR are therefore fairly simple, requiring 1) that individual precordial leads, and not bipolar limb leads, be evaluated and 2) that TDR be present at baseline and significantly augmented as a result of an intervention. In a recent paper published in Heart Rhythm, Opthof and co-workers15 set out to test the hypothesis Tpeak-Tend interval reflects transmural dispersion. Plunge electrodes were used to quantitate transmural and global dispersion of Repolarization and Tpeak-Tend (Tp-e) was measured only in a single limb lead, lead II, under conditions in which TDR was essentially non-existent: 2.7-14.5 ms. The use of two anesthetics, propofol and isoflurane, known to suppress sodium channel currents in a variety of cells including M cells, together with the use of a pacing rate of 130 bpm, resulted in essentially no TDR. The recording of precordial ECGs was not possible in this open chest dog model. Thus the two fundamental criteria for validation were not met and the study as designed, for reasons discussed above, could come to no other conclusion than that reached, which is that “Tp-e does not correlate with transmural dispersion of Repolarization, but is an index of total dispersion of Repolarization”. Thus, the quest for direct validation or invalidation of Tpeak-Tend measured at the body surface as an index of TDR remains unfulfilled. Although most studies to date concur that Tpeak-Tend provides a measure of spatial dispersion of Repolarization, the extent to which an augmented Tpeak-Tend interval is prognostic of arrhythmic risk depends on the proximity of the regions displaying disparate Repolarization times (i.e., Repolarization gradient). Consequently, it would be helpful to know to what extent Tpeak-Tend provides an index of TDR, in which case the differences in refractoriness are ensured to be within close proximity. To this end, it is noteworthy that an ideal model in which to test the hypothesis is in the chronic atrioventricular (AV) block dog treated with IKr blockers, since changes in Tpeak-Tend could be accurately correlated with TDR in a model that displays prominent TDR, and additionally correlated with the risk for development of TdP.
Nicholas L. Simmons - One of the best experts on this subject based on the ideXlab platform.
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A Voltage-Dependent Ca^2+ Influx Pathway Regulates the Ca^2+-Dependent Cl^− Conductance of Renal IMCD-3 Cells
Journal of Membrane Biology, 2009Co-Authors: John E. Linley, S. H. Boese, Nicholas L. Simmons, Michael A. GrayAbstract:We have previously shown that the membrane conductance of mIMCD-3 cells at a holding potential of 0 mV is dominated by a Ca^2+-dependent Cl^− current (I_CLCA). Here we report that I_CLCA activity is also voltage dependent and that this dependence on voltage is linked to the opening of a novel Al^3+-sensitive, voltage-dependent, Ca^2+ influx pathway. Using whole-cell patch-clamp recordings at a physiological holding potential (−60 mV), I_CLCA was found to be inactive and resting currents were predominantly K^+ selective. However, membrane depolarization to 0 mV resulted in a slow, sigmoidal, activation of I_CLCA ( T _0.5 ~ 500 s), while Repolarization in turn resulted in a monoexponential decay in I_CLCA ( T _0.5 ~ 100 s). The activation of I_CLCA by depolarization was reduced by lowering extracellular Ca^2+ and completely inhibited by buffering cytosolic Ca^2+ with EGTA, suggesting a role for Ca^2+ influx in the activation of I_CLCA. However, raising bulk cytosolic Ca^2+ at −60 mV did not produce sustained I_CLCA activity. Therefore I_CLCA is dependent on both an increase in intracellular Ca^2+ and depolarization to be active. We further show that membrane depolarization is coupled to opening of a Ca^2+ influx pathway that displays equal permeability to Ca^2+ and Ba^2+ ions and that is blocked by extracellular Al^3+ and La^3+. Furthermore, Al^3+ completely and reversibly inhibited depolarization-induced activation of I_CLCA, thereby directly linking Ca^2+ influx to activation of I_CLCA. We speculate that during sustained membrane depolarization, calcium influx activates I_CLCA which functions to modulate NaCl transport across the apical membrane of IMCD cells.
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A voltage-dependent Ca2+ influx pathway regulates the Ca 2+-dependent Cl- conductance of renal IMCD-3 cells
Journal of Membrane Biology, 2009Co-Authors: John E. Linley, S. H. Boese, Nicholas L. Simmons, Michael A. GrayAbstract:We have previously shown that the membrane conductance of mIMCD-3 cells at a holding potential of 0 mV is dominated by a Ca2+-dependent Cl(-) current (I(CLCA)). Here we report that I(CLCA) activity is also voltage dependent and that this dependence on voltage is linked to the opening of a novel Al3+-sensitive, voltage-dependent, Ca2+ influx pathway. Using whole-cell patch-clamp recordings at a physiological holding potential (-60 mV), ICLCA was found to be inactive and resting currents were predominantly K+ selective. However, membrane depolarization to 0 mV resulted in a slow, sigmoidal, activation of ICLCA (T(0.5) approximately 500 s), while Repolarization in turn resulted in a monoexponential decay in I(CLCA) (T (0.5) approximately 100 s). The activation of I(CLCA) by depolarization was reduced by lowering extracellular Ca2+ and completely inhibited by buffering cytosolic Ca2+ with EGTA, suggesting a role for Ca2+ influx in the activation of I(CLCA). However, raising bulk cytosolic Ca2+ at -60 mV did not produce sustained I(CLCA) activity. Therefore I(CLCA) is dependent on both an increase in intracellular Ca2+ and depolarization to be active. We further show that membrane depolarization is coupled to opening of a Ca2+ influx pathway that displays equal permeability to Ca2+ and Ba2+ ions and that is blocked by extracellular Al3+ and La3+. Furthermore, Al3+ completely and reversibly inhibited depolarization-induced activation of ICLCA, thereby directly linking Ca2+ influx to activation of I(CLCA). We speculate that during sustained membrane depolarization, calcium influx activates ICLCA which functions to modulate NaCl transport across the apical membrane of IMCD cells.
