Volume-activated chloride channels in mice Leydig cells.
June 27th, 2008 | by admin |Volume-activated chloride channels in mice Leydig cells.
Production and secretion of testosterone in Leydig cells are mainly controlled by the luteinizing hormone (LH). Biochemical evidences suggest that the activity of Cl(-) ions can modulate the steroidogenic process, but the specific ion channels involved are not known. Here, we extend the characterization of Cl(-) channels in mice Leydig cells (50-60 days old) by describing volume-activated Cl(-) currents (I(Cl,swell)). The amplitude of I(Cl,swell) is dependent on the osmotic gradient across the cell membrane, with an apparent EC(50) of approximately 75 mOsm. These currents display the typical biophysical signature of volume-activated anion channels (VRAC): dependence on intracellular ATP, outward rectification, inactivation at positive potentials, and selectivity sequence (I(- )> Cl(- )> F(-)). Staurosporine (200 nM) did not block the activation of I(Cl,swell). The block induced by 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB; 128 muM), SITS (200 muM), ATP (500 muM), pyridoxal-phosphate-6-azophenyl-2\’,4\’-disulfonate (PPADS; 100 muM), and Suramin (10 muM) were described by the permeant blocker model with apparent dissociation constant at 0 mV [Formula: see text] and fractional distance of the binding site (delta) of 334 muM and 47 %, 880 muM and 35 %, 2,100 muM and 49%, 188 muM and 27%, and 66.5 muM and 49%, respectively. These numbers were derived from the peak value of the currents. We conclude that I(Cl,swell) in Leydig cells are activated independently of purinergic stimulation, that Suramin and PPADS block these currents by a direct interaction with VRAC and that ATP is able to permeate this channel.
Poletto Chaves LA, Varanda WA.
Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Av. Bandeirantes 3900, 14049-900, Ribeirão Preto/SP, Brazil.