Calmodulin-regulated, ATP-driven calcium transport by basolateral membranes of rat small intestine.

Abstract

Uptake of calcium by a membrane fraction enriched in basolateral plasma membrane vesicles from rat small intestine has been investigated using a rapid filtration technique. Calcium accumulation is stimulated by ATP and released by the calcium ionophore A23187. Kinetic studies indicate a calcium concentration of 28 nM for half-maximal stimulation of ATP-driven uptake. Transport is minimally inhibited by oligomycin and ouabain but is reduced 40% by lanthanum and abolished by 50 microM vanadate. The ATP-dependent calcium uptake is stimulated by the calcium regulatory protein, calmodulin, in a dose-dependent fashion. Calmodulin increases both the maximal transport rate and the calcium affinity of the transport mechanism. These results are consistent with the existence of an ATP-dependent, calmodulin-regulated calcium transport mechanism in the basolateral plasma membrane of intestinal epithelial cells, and suggests that calmodulin may modulate transepithelial calcium absorption in addition to controlling cytosolic calcium levels.