CLONING AND CHARACTERIZATION OF MAXI K-SUBUNIT IN RABBIT KIDNEY( CHANNEL ALPHA)

We have identified in rabbit renal cells two alternatively spliced tra nscripts Of the alpha-subunit rbslo1 and rbslo2. Rbslo1 has a novel '' in-frame'' 174-bp insertion immediately after the predicted S8 transme mbrane segment, whereas rbslo2 has a 104-bp deletion between S9 and S1 0, creating a frameshift and a premature termination codon. Amino acid identity between mouse maxi K+ channel alpha-subunit (mslo) and rbslo 1 was 99%. Two transcript sizes of 4.2 and 7.5 kb were detected in bra in, kidney, stomach, testis, and lung. Rbslo is expressed in glomeruli , thin limbs Of Henle's loop, medullary and cortical thick ascending l imbs of Henle's loop, and cortical, outer, and inner medullary collect ing ducts; however, it was rarely detected in proximal convoluted tubu les. Rbslo1 is most abundant in inner medulla. Expressed in Xenopus oo cytes, 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 t ranscripts are expressed in multiple nephron segments and that the mag nitude of mRNA expression varies among different nephron segments.