Cloning and functional expression of a novel isoform of ROMK inwardly rectifying ATP‐dependent K+ channel, ROMK6 (Kir1.1 f)

Abstract
We have identified from rat kidney a novel isoform of ROMK/Kir1.1, designated ROMK6/Kir1.1f. ROMK6 was nearly identical to ROMK1, but possessed an 122‐bp insertion in the 5′ region. Its deduced amino acid sequence was shorter by 19 amino acids than that of ROMK1 in the amino‐terminus. Unlike other previously reported ROMK isoforms, ROMK6 mRNA was ubiquitously expressed in various tissues, including kidney, brain, heart, liver, pancreas and skeletal muscle. Xenopus oocytes injected with ROMK6 cRNA expressed a Ba2+‐sensitive weakly inwardly rectifying K+ current. These results indicate that ROMK6 is a novel functional K+ channel and might be involved in K+ secretion in various tissues.