We have constructed a detailed physical map of the 35 Mb region spanning human chromosome Xp22.3-Xp21.3. The backbone of the map is represented by a single oriented contiguous stretch of 585 overlapping yeast artificial chromosome (YAC) clones covering the entire region. The map is formatted with 615 map objects that include 324 YACs, 185 sequence tagged sites, 28 genes, 85 chromosomal breakpoints and 37 highly polymorphic markers. Physical mapping was both guided and confirmed using 183 bins defined by chromosomal breakpoints and by overlapping regions of YAC clones. The localization of polymorphic markers in the physical map permits the integration of physical and genetic data across the region. These data establish chromosome Xp22.3-Xp21.3 as one of the best characterized large regions in the human genome. The map should greatly facilitate finer scale mapping and sequencing as well as the identification of disease genes from this portion of the human genome.

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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.

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