Purpose of review: A variety of K+ channels have been identified with the patch-clamp technique and molecular cloning in the kidney. However, it is still a challenging task to determine the location and function of the cloned K+ channels in the corresponding nephron segment. The aim of the present review is to update the recent developments regarding the location and function of the cloned K+ channels in the native tubule. Also, the review describes the new regulatory mechanism of renal outer-medullary K (ROMK) channels and the role of Ca(2+)-activated maxi K+ channels in flow-dependent K+ secretion.
Recent findings: Several types of voltage-gated K+ (Kv) channel, such as KCNQ1, KCNA10 and Kv1.3, are highly expressed at the apical membrane of proximal tubules and distal tubules. They may participate in stabilizing the cell membrane potential. Moreover, studies performed in ROMK-knockout mice have shown that the apical 70 pS K+ channel is absent in the thick ascending limb in these mice, suggesting that the ROMK channel is also involved in forming the apical 70 pS K+ channel in the thick ascending limb. Three important kinases, protein tyrosine kinase, serum- and glucocorticoid-inducible kinase and with-no-lysine kinase, have been suggested to regulate the ROMK channel density in the cortical collecting duct. Low K+ intake increases protein tyrosine kinase expression and tyrosine phosphorylation of ROMK channels. Coexpression of with-no-lysine kinase with the ROMK channel decreases K+ current whereas serum- and glucocorticoid-inducible kinase 1 stimulates the ROMK current in oocytes in the presence of Na/H exchanger regulatory factor 2. The Ca-activated maxi K+ channel has been shown to be activated by an increase in flow rate in the rabbit cortical collecting duct.
Summary: The voltage-gated K+ channels are expressed in a variety of nephron segments and play a role in stabilization of cell membrane potential. With-no-lysine kinase and serum- and glucocorticoid-inducible kinase 1 have been shown to regulate ROMK1 channels. Protein tyrosine kinase mediates the effect of K+ intake on K+ secretion by stimulation of tyrosine phosphorylation of ROMK1 channels. The Ca-activated maxi K+ channel plays a role in flow-dependent K+ secretion in the distal nephron.