Growth hormone regulates the distribution of L-type calcium channels in rat adipocyte membranes

Earlier studies demonstrated that deprivation of growth hormone (GH) for >/=3 h decreased basal and maximally stimulated cytosolic Ca2+ in rat adipocytes and suggested that membrane Ca2+ channels might be decreased. Measurement of L-type Ca2+ channels in purified plasma membranes by immunoassay or dihydropyridine binding indicated a two- to fourfold decrease after 3 h of incubation without GH. No such decrease was seen in unfractionated adipocyte membrane preparations. The decrease in plasma membrane channel content was largely accounted for by redistribution of channels to a light microsomal membrane fraction. Immunoassay of alpha1-, alpha2/delta-, and beta-channel subunits in membrane fractions indicated that the channels redistributed as intact complexes. Addition of GH during the 1st h of incubation prevented channel redistribution, and addition of GH after 3 h restored channel distribution to the GH-replete state of freshly isolated adipocytes. The studies suggest that GH may regulate the abundance of Ca2+ channels in the adipocyte plasma membrane and thereby modulate sensitivity to signals, the expression of which is Ca2+ dependent.