title: Regulation of 22Na+ transport by calcium in an established kidney epithelial cell line.
abstract: The role of calcium in regulating the Na+ channel in an established kidney epithelial cell line has been examined. Extracellular calcium was inhibitory to Na+ uptake, and a Dixon plot of the initial Na+ uptake rate in the presence of Ca2+ was nonlinear, suggesting a mixed pattern of inhibition. Similar patterns of inhibition were also observed for other divalent cations, including Ba2+, Mg2+, and Mn2+. In contrast elevated concentrations of intracellular calcium resulted in a stimulation of Na+ entry. This intracellular effect was specific to calcium, with Mg2+ and Mn2+ appearing much less effective. Lineweaver-Burk plots of Na+ influx in calcium-loaded and unloaded cells were linear, suggesting that under both conditions a single system transported Na+. Although Na+ entry was stimulated by intracellular Ca2+, the cells did not exhibit other counter transport phenomena reported with cell types in which a Na+/Ca2+ exchange system is operative. Thus, the results indicate that calcium acts as an allosteric regulator of Na+ transport by the Na+ channel.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002460:Cell Line; D004285:Dogs; D004848:Epithelium / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*
chemical_list: D000001:Calcimycin; D012964:Sodium; D008274:Magnesium; D002118:Calcium