Separation of two Cl(-) currents in cultured human and murine mesangial cells: biophysical and pharmacological characteristics of I(Cl.vol) and I(Cl.Ca).

Mesangial cells, a combined smooth muscle- and fibroblast-like phenotype, are important regulators of renal function. These cells exist in a region of variable osmolarity and may require Cl(-) channels for volume regulation. Additionally, Ca(2+)-activated Cl(-) channels in these cells may participate in Ca(2+)-dependent contractile responses to vasoactive agonists. Relatively little, however, is known about mesangial cell Cl(-) currents (I(Cl)); including the biophysical description and pharmacological characterization. We used whole-cell patch clamp to study I(Cl) in cultured human and SV40-transformed murine mesangial cells. I(Cl) was measured in cells dialyzed and bathed with symmetrical N-methyl-D-glucamine chloride solutions to minimize cation currents. Dialysis with buffers to control intracellular Ca(2+) ([Ca(2+)](i)), extracellular solutions of varied osmolarity, and manipulation of the transmembrane Cl(-) gradient were used to separate two currents: I(Cl.vol) (volume-sensitive), and I(Cl.Ca) (Ca(2+)-activated). In symmetrical Cl(-) with low [Ca(2+)](i), I(Cl.vol) was outwardly rectifying and modulated by osmolarity. I(Cl.vol) demonstrated slight time- and voltage-dependent inactivation. In symmetrical Cl(-) with elevated [Ca(2+)](i) and hypertonic bath, I(Cl.Ca) was linear, but in asymmetrical Cl(-) (low [Cl(-)](i)) was outwardly rectifying and demonstrated time- and voltage-dependent activation. Permeability sequences for both I(Cl.vol) and I(Cl.Ca) were I(-) > Br(-) > Cl(-) > F(-); however, there were differences in the relative magnitudes. Tamoxifen inhibited I(Cl.vol) more potently than I(Cl.Ca), whereas niflumic acid inhibited I(Cl.Ca) more potently than I(Cl.vol). We have separated and characterized two types of I(Cl) in cultured human and murine mesangial cells. I(Cl.Ca) and I(Cl.vol) have different biophysical and pharmacological characteristics. These observations on I(Cl.Ca) and I(Cl.vol) may provide insight into mesangial cell reactivity and volume regulation. Copyright 2002 S. Karger AG, Basel