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-Alawas 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.