Potassium secretion by the cortical collecting tubule: effect of C1 gradients and ouabain.

In various epithelia K and Cl transport are molecularly coupled and KCl cotransport is dependent on the Na-K pump. The present study examines 1) the effect of a bath-to-lumen Cl gradient on K secretion during active Na transport and 2) the effect of basolateral ouabain on K secretion and Na absorption in the presence and the absence of a bath-to-lumen Cl gradient. Under symmetrical conditions there was significant K secretion (JK = -24.0 +/- 3.9 pmol.mm-1.min-1) and Cl secretion (JCl = -15.7 +/- 3.7 pmol.mm-1.min-1). Transepithelial voltage (VT) was significantly lumen negative (-25.3 +/- 5.9 mV), and Cl secretion occurred against its electrochemical gradient by a transcellular mechanism. Increasing bath [Cl] did not hyperpolarize VT; in fact there was a tendency for VT to depolarize and K secretion was not stimulated. However, ouabain significantly inhibited active Cl secretion and net Na absorption both in the presence and absence of a bath-to-lumen Cl gradient. Furthermore, ouabain totally inhibited K secretion in the absence of external ion gradients but inhibited K secretion by only 50% in the presence of a bath-to-lumen Cl gradient. This ouabain-insensitive K secretion exhibited a codependence on Cl secretion. Thus K secretion may occur passively, utilizing Cl movement down its electrochemical gradient when active Na transport is inhibited by ouabain. The results are compatible with the presence of a Cl-linked K-secretory process in the rabbit CCT.(ABSTRACT TRUNCATED AT 250 WORDS)