Expression of HKα2 protein is increased selectively in renal medulla by chronic hypokalemia

Abstract

Our laboratory has demonstrated by Northern analysis that chronic hypokalemia increases HKα2 (i.e., α-subunit of the colonic H+-K+-ATPase) mRNA abundance in the rat. To determine whether the increase in mRNA correlated with an increase in HKα2 protein, an antibody was raised against a synthetic peptide derived from amino acids 686–698 of the HKα2sequence. The anti-HKα2 antibody hybridized to rat distal colon membranes which migrated at ∼100 kDa (expected mobility of HKα2). HKα2 protein was not detected in plasma membranes from rat whole kidney or stomach (100 μg) derived from control animals. The antibody was then used to investigate changes in expression of HKα2 in renal cortex, renal medulla, and distal colon in two pathophysiological conditions: 1) chronic hypokalemia (LK) and 2) chronic metabolic acidosis (CMA). In LK rats there was a marked, but selective, increase in the abundance of HKα2 protein in membranes prepared from renal medulla. Nevertheless, a corresponding increase in HKα2 protein abundance was not observed in membranes prepared from the distal colon of LK rats. HKα2 protein abundance in CMA was indistinguishable from controls. Moreover, chronic hypokalemia had no effect on expression of α1-Na+-K+-ATPase or HKα1 in kidney or distal colon under any experimental condition. Therefore, HKα2 protein is tissue- and site-specifically upregulated in response to chronic hypokalemia but not by CMA. Furthermore, this regulatory response is localized to the renal medulla.