Na+-alanine uptake activates a Cl- conductance in frog renal proximal tubule cells via nonconventional PKC.

Abstract

Hyposmotically induced swelling of frog renal proximal tubule cells activates a DIDS-sensitive, outwardly rectifying Cl- conductance via a conventional protein kinase C (PKC). This study examines whether Na+-alanine cotransport similarly activates a DIDS-sensitive Cl- conductance in frog renal proximal tubule cells. On stimulation of Na+-alanine cotransport, the DIDS-sensitive current (I(DIDS-Ala)) increased markedly over time. I(DIDS-Ala) exhibited outward rectification, a Na+/Cl- selectivity ratio of 0.19 +/- 0.03, and an anion selectivity sequence Br- = Cl- > I- > gluconate-. Activation of I(DIDS-Ala) was dependent on ATP hydrolysis and PKC-mediated phosphorylation and was inhibited by hyperosmotic conditions. Activation could be not ascribed to a conventional PKC isoform, as I(DIDS-Ala) was not affected by removing Ca2+ or by phorbol ester treatment, suggesting a role for a nonconventional PKC isoform, either novel or atypical. We conclude that Na+-alanine cotransport activates a DIDS-sensitive Cl- conductance via a nonconventional PKC isoform. This contrasts with the hyposmotically activated Cl- conductance, which requires conventional PKC activation.