Vasopressin and PGE2 regulate activity of apical 70 pS K+ channel in thick ascending limb of rat kidney

Abstract

Vasopressin and prostaglandin E2 (PGE2) are involved in regulating NaCl reabsorption in the thick ascending limb (TAL) of the rat kidney. In the present study, we used the patch-clamp technique to study the effects of vasopressin and PGE2 on the apical 70 pS K+ channel in the rat TAL. Addition of vasopressin increased the channel activity, defined as NP o, from 1.11 to 1.52 (200 pM) and 1.80 (500 pM), respectively. The effect of vasopressin can be mimicked by either forskolin (1–5 μM) or 8-bromo-cAMP/dibutyryl-cAMP (8-Br-cAMP/DBcAMP) (200–500 μM). Moreover, the effects of cAMP and vasopressin were not additive and application of 10 μM H-89 abolished the effect of vasopressin. This suggests that the effect of vasopressin is mediated by a cAMP-dependent pathway. Applying 10 nM PGE2 alone had no significant effect on the channel activity. However, PGE2 (10 nM) abolished the stimulatory effect of vasopressin. The PGE2-induced inhibition of the vasopressin effect was the result of decreasing cAMP production because addition of 200 μM 8-Br-cAMP/DBcAMP reversed the PGE2-induced inhibition. In addition to antagonizing the vasopressin effect, high concentrations of PGE2 reduced channel activity in the absence of vasopressin by 33% (500 nM) and 51% (1 μM), respectively. The inhibitory effect of high concentrations of PGE2 was not the result of decreasing cAMP production because adding the membrane-permeant cAMP analog failed to restore the channel activity. In contrast, inhibiting protein kinase C (PKC) with calphostin C (100 nM) abolished the effect of 1 μM PGE2. We conclude that PGE2 inhibits apical K+ channels by two mechanisms: 1) low concentrations of PGE2 attenuate the vasopressin-induced stimulation mainly by reducing cAMP generation, and 2) high concentrations of PGE2 inhibit the channel activity by a PKC-dependent pathway.