Abstract
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 Kcnj10. 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 Ca(2+) 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 Ca(2+) 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 Ca(2+) 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.NEW & NOTEWORTHY It is not known whether CaSR also inhibits Kir4.1/Kir5.1 in the native DCT. We have now used the patch-clamp experiments to directly demonstrate that the stimulation of CaSR in the basolateral membrane is able to inhibit Kir4.1/Kir5.1 in the mouse DCT and depolarize the DCT membrane potential. We speculate that the stimulation of CaSR-induced inhibition of Kir4.1/Kir5.1 may play a role in decreasing kidney Ca(2+) excretion during hypocalcemia.