Platelet-derived growth factor activation of gastric mucosal calcium channels.

Gastric mucosal calcium channel complex was isolated from the solubilized epithelial cell membranes by affinity chromatography on wheat germ agglutinin. The complex following labeling with 3H]PN200-100 was reconstituted into phospholipid vesicles which exhibited active 45Ca2+ uptake. The channels responded in a dose dependent manner to dihydropyridine calcium antagonist, PN200-110, which at 0.5 microM exerted maximal inhibitory affect of 66% on 45Ca2+ uptake, while a 52% enhancement in 45Ca2+ uptake occurred with a specific calcium channel activator, BAY K8644. On platelet-derived growth factor (PDGF) binding in the presence of ATP, channels showed an increase in protein tyrosine phosphorylation of 55 and 170kDa subunits of calcium channel. Such phosphorylated channels following reconstitution into vesicles displayed a 78% greater 45Ca2+ uptake. The results point towards the importance of PDGF in the regulation of gastric mucosal calcium homeostasis.