title: A voltage-dependent Ca2+ influx pathway regulates the Ca2+-dependent Cl(-) conductance of renal IMCD-3 cells.
abstract: 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.
authors: Epithelial Research Group, Institute for Cell and Molecular Biosciences, Medical School, Newcastle University, Newcastle upon Tyne NE2-4HH, UK.
authors: John E
authors: JE
authors: Linley
authors: Stefan H
authors: SH
authors: Boese
authors: Nicholas L
authors: NL
authors: Simmons
authors: Michael A
authors: MA
authors: Gray
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002460:Cell Line; D018118:Chloride Channels / Q000502:physiology*; D002713:Chlorine / Q000378:metabolism*; D004553:Electric Conductivity; D015640:Ion Channel Gating / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice
chemical_list: D018118:Chloride Channels; D002713:Chlorine; D002118:Calcium