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

Abstract

Vasopressin and prostaglandin E(2) (PGE(2)) 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 PGE(2) 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 microM) or 8-bromo-cAMP/dibutyryl-cAMP (8-Br-cAMP/DBcAMP) (200-500 microM). Moreover, the effects of cAMP and vasopressin were not additive and application of 10 microM H-89 abolished the effect of vasopressin. This suggests that the effect of vasopressin is mediated by a cAMP-dependent pathway. Applying 10 nM PGE(2) alone had no significant effect on the channel activity. However, PGE(2) (10 nM) abolished the stimulatory effect of vasopressin. The PGE(2)-induced inhibition of the vasopressin effect was the result of decreasing cAMP production because addition of 200 microM 8-Br-cAMP/DBcAMP reversed the PGE(2)-induced inhibition. In addition to antagonizing the vasopressin effect, high concentrations of PGE(2) reduced channel activity in the absence of vasopressin by 33% (500 nM) and 51% (1 microM), respectively. The inhibitory effect of high concentrations of PGE(2) 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 microM PGE(2). We conclude that PGE(2) inhibits apical K(+) channels by two mechanisms: 1) low concentrations of PGE(2) attenuate the vasopressin-induced stimulation mainly by reducing cAMP generation, and 2) high concentrations of PGE(2) inhibit the channel activity by a PKC-dependent pathway.

Arachidonic acid inhibits K channels in basolateral membrane of the thick ascending limb

“…The COX-dependent AA metabolites such as PGE 2 have been shown to attenuate the stimulatory effect of vasopressin on Cl reabsorption (7). We have previously demonstrated that PGE 2 at low concentrations (Ͻ1 M) abolished the vasopressin-induced increase in the activity of the apical 70-pS K channel, whereas PGE 2 at high concentrations decreased the activity of the 70-pS K channel by a PKC-dependent mechanism (18). In addition to PGE 2 , the cytochrome P-450-dependent metabolites of AA, such as 20-HETE, have been indicated as potent inhibitors of the Na-K-2Cl cotransporters (9) and the apical 70-pS K channel in the mTAL (27).…”

Endogenous flow-induced superoxide stimulates Na/H exchange activity via PKC in thick ascending limbs

“…PKC is required for angiotensin IIstimulated Na-K-2Cl cotransporter activity (2) and indirectly stimulates Na bicarbonate absorption (14). In addition, a PKC-dependent pathway mediates inhibition of apical K ϩ channel activity caused by high concentrations of prostaglandin E 2 (31).…”

Calcium-sensing receptor signaling pathways in medullary thick ascending limb cells mediate COX-2-derived PGE2production: functional significance

“…Short-term regulation of NKCC2 has also been observed and involves effects on both activity and trafficking (18,24,43,44,47). CYP450-and COX-derived metabolites of arachidonic acid (AA) inhibit ion transport in the mTAL by several different mechanisms including interactions with apical K ϩ channels and NKCC2 (32,37,38,52,53). Thus, it is important to understand how molecules that act in the TAL affect AA metabolism since regulation of ion transport in this segment may occur in response to signals induced by receptor activation (20,21,58,60).…”