Cloning of rabbit Kir6.1, SUR2A, and SUR2B:: possible candidates for a renal KATP channel

In rabbit proximal tubules, a basolateral ATP- and taurine-sensitive K+ channel (K-ATP) was shown to be involved in the regulation of the basolateral K+ conductance as a function of the rate of apical Na+ entry. To establish the molecular identity of this channel, we used degenerated primers to look for cDNA transcripts for an inwardly rectifying K+ channel (Kir6.1 and Kir6.2) and sulfonylurea receptors (SUR1, SUR2A, and SUR2B) in a cDNA library obtained from rabbit proximal tubules. PCR products were found only for Kir6.1, SUR2A, and SUR2B. Expression of Kir6.1 in Xenopus oocytes generated an additional K+ current that was found to be sensitive to external barium and intracellular taurine and to changes in intracellular ATP concentrations. To study the specificity of the taurine sensitivity, intracellular taurine was tested on several members of the Kir family expressed in Xenopus oocytes. K+ currents induced by Kir1.1A, Kir2.1, Kir3.2, Kir4.1, or Kir5.1 were insensitive to taurine, but all tested combinations of Kir6.x with or without the SUR subunit were significantly inhibited by taurine. This study suggests that the taurine-sensitive K-ATP channel of rabbit proximal tubules is formed by a combination of Kir6.1 plus SUR2A and/or SUR2B.