Stimulation of Ca ²⁺-sensing receptor inhibits the basolateral 50-pS K channels in the thick ascending limb of rat kidney

We used the patch-clamp technique to study the effect of changing the external Ca ²⁺ on the basolateral 50-pS K channel in the thick ascending limb (TAL) of rat kidney. Increasing the external Ca ²⁺ concentration from 1mM to 2 or 3mM inhibited the basolateral 50-pS K channels while decreasing external Ca ²⁺ to 10μM [U+F020]increased the 50-pS K channel activity. The effect of the external Ca ²⁺ on the 50-pS K channels was observed only in cell-attached patches but not in excised patches. Moreover, the inhibitory effect of increasing external Ca ²⁺ on the 50-pS K channels was absent in the presence of NPS2390, an antagonist of Ca ²⁺-sensing receptor (CaSR), suggesting that the inhibitory effect of the external Ca ²⁺ was the result of stimulation of the CaSR. Application of the membrane-permeable cAMP analog increased the 50-pS K channel activity but did not block the effect of raising the external Ca ²⁺ on the K channels. Neither inhibition of phospholipase A2 (PLA ₂) nor suppression of cytochrome P450-ω-hydroxylation-dependent metabolism of arachidonic acid was able to abolish the effect of raising the external Ca ²⁺ on the 50-pS K channels. In contrast, inhibition of phospholipase C (PLC) or blocking protein kinase C (PKC) completely abolished the inhibition of the basolateral 50-pS K channels induced by raising the external Ca ²⁺. We conclude that the external Ca ²⁺ concentration plays an important role in the regulation of the basolateral K channel activity in the TAL and that the effect of the external Ca ²⁺ is mediated by the CaSR which stimulates PLC-PKC pathways. The regulation of the basolateral K channels by the CaSR may be the mechanism by which extracellular Ca ²⁺ level modulates the reabsorption of divalent cations.