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A Voltage-Dependent Ca2+ Influx Pathway Regulates the Ca2+-Dependent Cl- Conductance of Renal IMCD-3 Cells

Lookup NU author(s): John Linley, Dr Stefan Boese, Professor Nicholas Simmons, Dr Michael Gray

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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), 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) similar to 500 s), while repolarization in turn resulted in a monoexponential decay in I-CLCA (T (0.5) similar to 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 I-CLCA, thereby directly linking Ca2+ 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.

Publication metadata

Author(s): Linley JE, Boese SH, Simmons NL, Gray MA

Publication type: Article

Publication status: Published

Journal: Journal of Membrane Biology

Year: 2009

Volume: 230

Issue: 2

Pages: 57-68

Date deposited: 10/05/2010

ISSN (print): 0022-2631

ISSN (electronic): 1432-1424

Publisher: Springer

URL: http://dx.doi.org/10.1007/s00232-009-9186-0

DOI: 10.1007/s00232-009-9186-0

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