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

Abstract

We have used the patch-clamp technique to study the effect of arachidonic acid (AA) on the basolateral K channels in the medullary thick ascending limb (mTAL) of rat kidney. An inwardly rectifying 50-pS K channel was identified in cell-attached and inside-out patches in the basolateral membrane of the mTAL. The channel open probability (Po) was 0.51 at the spontaneous cell membrane potential and decreased to 0.25 by 30 mV hyperpolarization. The addition of 5 M AA decreased channel activity, identified as NPo, from 0.58 to 0.08 in cell-attached patches. The effect of AA on the 50-pS K channel was specific because 10 M cis-11,14,17-eicosatrienoic acid had no significant effect on channel activity. To determine whether the effect of AA was mediated by AA per se or by its metabolites, we examined the effect of AA on channel activity in the presence of indomethacin, an inhibitor of cyclooxygenase, or N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), an inhibitor of cytochrome P-450 monooxygenase. Inhibition of cyclooxygenase increased channel activity from 0.54 to 0.9. However, indomethacin did not abolish the inhibitory effect of AA on the 50-pS K channel. In contrast, inhibition of cytochrome P-450 metabolism not only increased channel activity from 0.49 to 0.83 but also completely abolished the effect of AA. Moreover, addition of DDMS can reverse the inhibitory effect of AA on channel activity. The notion that the effect of AA was mediated by cytochrome P-450-dependent metabolites of AA is also supported by the observation that addition of 100 nM of 20-hydroxyeicosatetraenoic acid, a main metabolite of AA in the mTAL, can mimic the effect of AA. We conclude that AA inhibits the 50-pS K channel in the basolateral membrane of the mTAL and that the effect of AA is mainly mediated by cytochrome P-450-dependent metabolites of AA.cyclooxygenase; cytochrome P-450 -oxidation; 20-hydroxyeicosatetraenoic acid; basolateral K channel K CHANNELS IN THE BASOLATERAL membrane of the medullary thick ascending limb (mTAL) play an important role in the regulation of epithelial transport in the loop of Henle. The basolateral K channels in the mTAL are responsible for K recycling across the basolateral membrane and participate in generating the cell membrane potential (Fig.

Adenosine stimulates the basolateral 50 pS K channels in the thick ascending limb of the rat kidney

“…Because the basolateral membrane potential determines the electrochemical gradient for Cl exit across the basolateral membrane, alteration of the cell membrane potential should affect the Cl exit across the basolateral membrane and indirectly the activity of the Na/Cl/K cotransporter in the apical membrane. Several types of basolateral K channels have been identified with patch-clamp experiments (8,19). We and others have confirmed that a 50 pS inwardly rectifying K channel was highly active in the basolateral membrane.…”

Calcium-sensing Receptor Stimulates Luminal K+-dependent H+ Excretion in Medullary Thick Ascending Limbs of Henle's Loop of Mouse Kidney

“…The observations that activating mutations of the human CaSR gene can cause a Bartter's-like phenotype further support this concept (Watanabe et al 2002). Other studies have demonstrated that P-450-dependent metabolites of arachidonic acid most likely 20-HETE , as well as Mg 2+ and spermine, which are known as potent calcimimetics, and low pHi inhibit basolateral membrane 50-pS K channels in TAL (Gu et al 2002;Paulais et al 2002) This basolateral K + conductance maintains driving force for the basolateral diffusion of Cl -and participates in the basolateral efflux of K + ions to partially compensate for the influx of K + ions associated with Na + -K + -ATPase activity. We found that CaSR-related alkalinization was still present under ambient Na + -free conditions, but was completely inhibited under apical K + -free conditions and by applications of HKa blockers Sch-28080 and ouabain.…”

Basolateral membrane K+channels in renal epithelial cells

“…However, the authors have been unable to ascertain to which specific K ϩ channel gene families these K ϩ channels belong. Unclassified channels are reported in the basolateral membrane of PT cells (7, 32, 33, 51-53, 62, 63, 97, 111, 125), TAL cells (24,39,40), DCT cells (123), and CNT/CD cells (36,(47)(48)(49)82).…”