Cloning and characterization of maxi K⁺ channel α-subunit in rabbit kidney

We have identified in rabbit renal cells two alternatively spliced transcripts of the α-subunit rbslo1 and rbslo2. Rbslo1 has a novel 'in- frame' 174-bp insertion immediately after the predicted S8 trans-membrane segment, whereas rbslo2 has a 104-bp deletion between S9 and S10, creating a frameshift and a premature termination codon. Amino acid identity between mouse maxi K⁺ channel α-subunit (mslo) and rbslo1 was 99%. Two transcript sizes of 4.2 and 7.5 kb were detected in brain, kidney, stomach testis and lung. Rbslo is expressed in glomeruli, thin limbs of Henle's loop, medullary and cortical thick ascending limbs of Henle's loop, and cortical, outer, and tuner medullary collecting ducts; however, it was rarely detected in proximal convoluted tubules. Rbslo1 is most abundant in inner medulla. Expressed in Xenopus oocytes, rbslo1 generates depolarization-activated, outwardly rectifying K⁺ currents. Rbslo1 expressed in Chinese hamster ovary cells could be activated by depolarization and Ca²⁺. These data suggest that rbslo transcripts are expressed in multiple nephron segments and that the magnitude of mRNA expression varies among different nephron segments.