2 HIGHLY HOMOLOGOUS MEMBERS OF THE CLC CHLORIDE CHANNEL FAMILY IN BOTH RAT AND HUMAN KIDNEY

We have cloned two closely related putative Cl- channels from both rat kidney (designated rClC-K1 and rClC-K2) and human kidney (hClC-Ka and hClC-Kb) by sequence homology to the ClC family of voltage-gated Cl- channels. While rClC-K1 is nearly identical to ClC-K1, a channel recen tly isolated by a similar strategy, rClC-K2 is 80% identical to rClC-K 1 and is encoded by a different gene. hClC-Ka and hClC-Kb show approxi mate to 90% identity, while being approximate to 80% identical to the rat proteins. All ClC-K gene products are expressed predominantly in t he kidney. While rClC-K1 is expressed strongly in the cortical thick a scending limb and the distal convoluted tubule, with minor expression in the S3 segment of the proximal tubule and the cortical collecting t ubule, rClC-K2 is expressed in all segments of the nephron examined, i ncluding the glomerulus. Since they are related more closely to each o ther than to the rat proteins, hClC-Ka and hClC-Kb cannot be regarded as strict homologs of rClC-K1 or rClC-K2. After injection of ClC-K cRN As into oocytes, corresponding proteins were made and glycosylated, th ough no additional Cl- currents were detectable. Glycosylation occurs between domains D8 and D9, leading to a revision of the transmembrane topology model for ClC channels.