Several papers reported the role of TASK2 channels in cell volume regulation and regulatory volume decrease (RVD). To check the possibility that the TASK2 channel modulates the RVD process in kidney, we performed primary cultures of proximal convoluted tubules (PCT) and distal convoluted tubules (DCT) from wild-type and TASK2 knockout (KO) mice. In KO mice, the TASK2 coding sequence was in part replaced by the lac-Z gene. This allows for the precise localization of TASK2 in kidney sections using β-galactosidase staining. TASK2 was only localized in PCT cells. K+ currents were analyzed by the whole-cell clamp technique with 125 mM K-gluconate in the pipette and 140 mM Na-gluconate in the bath. In PCT cells from wild-type mice, hypotonicity induced swelling-activated K+ currents insensitive to 1 mM tetraethylammonium, 10 nM charybdotoxin, and 10 μM 293B, but blocked by 500 μM quinidine and 10 μM clofilium. These currents were increased in alkaline pH and decreased in acidic pH. In PCT cells from TASK2 KO, swelling-activated K+ currents were completely impaired. In conclusion, the TASK2 channel is expressed in kidney proximal cells and could be the swelling-activated K+ channel responsible for the cell volume regulation process during osmolyte absorptions in the proximal tubules.

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We have previously shown that despite the presence of mRNA encoding CFTR, renal proximal cells do not exhibit cAMP-sensitive Cl(-) conductance (Rubera I, Tauc M, Bidet M, Poujeol C, Cuiller B, Watrin A, Touret N, Poujeol P. Am J Physiol Renal Physiol 275: F651-F663, 1998). Nevertheless, in these cells, CFTR plays a crucial role in the control of the volume-sensitive outwardly rectifying (VSOR) activated Cl(-) currents during hypotonic shock. The aim of this study was to determine the role of CFTR in the regulation of apoptosis volume decrease (AVD) and the apoptosis phenomenon. For this purpose, renal cells were immortalized from primary cultures of proximal convoluted tubules from cftr(+/+) and cftr(-/-) mice. Apoptosis was induced by staurosporine (STS; 1 microM). Cell volume, Cl(-) conductance, caspase-3 activity, intracellular level of reactive oxygen species (ROS), and glutathione content (GSH/GSSG) were monitored during AVD. In cftr(+/+) cells, AVD and caspase-3 activation were strongly impaired by conventional Cl(-) channel blockers and by a specific CFTR inhibitor (CFTR(inh)-172; 5 microM). STS induced activation of CFTR conductance within 15 min, which was progressively replaced by VSOR Cl(-) currents after 60 min of exposure. In parallel, STS induced an increase in ROS content in the time course of VSOR Cl(-) current activation. This increase was impaired by CFTR(inh)-172 and was not observed in cftr(-/-) cells. Furthermore, the intracellular GSH/GSSG content decreased during STS exposure in cftr(+/+) cells only. In conclusion, CFTR could play a key role in the cascade of events leading to apoptosis. This role probably involves control of the intracellular ROS balance by some CFTR-dependent modulation of GSH concentration.