Stimulation of basolateral calcium-sensing receptor (CaSR) inhibits Kir4.1/Kir5.1 in the mouse distal convoluted tubule.

The calcium-sensing-receptor (CaSR) is expressed in the basolateral membrane of distal- convoluted-tubule (DCT) and CaSR expression inhibited Kir4.1 in cells expressing <i>Kcnj10</i>. The aim of the study is to explore whether CaSR inhibits Kir4.1/Kir5.1 in mouse DCT. We used patch-clamp technique to examine the effect of calcimimetics and increasing extracellular-Ca²⁺ level on the basolateral Kir4.1/Kir5.1 in the DCT. Application of R-568, a CaSR agonist, decreased the 40-pS inwardly-rectifying-K⁺ channel activity (Kir4.1/Kir5.1 heterotetramer), defined by NP_o (product of channel number and open probability), in the isolated DCT measured with cell-attached patches. This effect was completely abolished in the DCT treated with phospholipase-C (PLC) inhibitor or protein kinase C (PKC) inhibitor, suggesting that CaSR stimulation-induced inhibition of 40-pS K⁺ channel was due to activation of PLC-PKC pathway. Also, neomycin mimicked the effect of R-568 on the basolateral 40-pS K⁺ channel and decreased the 40-pS K⁺ channel activity. Again, this effect was completely abolished in the DCT treated with calphostin-C. Raising extracellular Ca²⁺ level to 5 mM reversibly inhibited the 40-pS K⁺ channel activity of the DCT and the washout was able to partially restore the channel activity. Moreover, the inhibition of PKC was able to completely abolish the inhibitory effect of 5 mM Ca²⁺ on the basolateral Kir4.1/Kir5.1 in the DCT. Finally, stimulation of CaSR with neomycin depolarized DCT cell membrane. We conclude that the activation of basolateral CaSR in the DCT inhibits Kir4.1/Kir5.1 and the effect of basolateral CaSR on the K⁺ channel is mediated by PLC-PKC pathway.