GROWTH-HORMONE REGULATES THE DISTRIBUTION OF L-TYPE CALCIUM CHANNELS IN RAT ADIPOCYTE MEMBRANES

Earlier studies demonstrated that deprivation of growth hormone (GH) f or greater than or equal to 3 h decreased basal and maximally stimulat ed cytosolic Ca2+ in rat adipocytes and suggested that membrane Ca2+ c hannels might be decreased. Measurement of L-type Ca2+ channels in pur ified plasma membranes by immunoassay or dihydropyridine binding indic ated a two- to fourfold decrease after 3 h of incubation without GH. N o such decrease was seen in unfractionated adipocyte membrane preparat ions. The decrease in plasma membrane channel content was largely acco unted for by redistribution of channels to a light microsomal membrane fraction. Immunoassay of alpha(1)-, alpha(2)/delta-, and beta-channel subunits in membrane fractions indicated that the channels redistribu ted as intact complexes. Addition of GH during the Ist h of incubation prevented channel redistribution, and addition of GH after 3 h restor ed channel distribution to the GH-replete state of freshly isolated ad ipocytes. The studies suggest that GH may regulate the abundance of Ca 2+ channels in the adipocyte plasma membrane and thereby modulate sens itivity to signals, the expression of which is Ca2+ dependent.