ACTIVATION OF DIHYDROPYRIDINE-SENSITIVE PAROTID SALIVARY-GLAND CALCIUM CHANNELS BY EPIDERMAL GROWTH-FACTOR

The calcium channel complex of the parotid was isolated from solubilized acinar-cell membranes by affinity chromatography on wheatgerm agglutinin. The channel, after labelling the calcium antagonist-receptor site with [H-3]-PN200-100, was reconstituted into phosphatidylcholine vesicles that exhibited active Ca-45(2+) uptake. This uptake was independent of sodium and potassium gradients, indicating its electroneutrality. The channels responded in a dose-dependent manner to the dihydropyridine calcium antagonist, PN200-110, which at 0.4 muM exerted a maximal inhibitory effect of 75% on Ca-45(2+) uptake; a 46% enhancement in Ca-45(2+) uptake occurred with a specific calcium-channel activator, BAY K8644. On epidermal growth-factor (EGF) binding in the presence of ATP, there was an increase in tyrosine phosphorylation of 55 and 170 kDa calcium-channel proteins. Such phosphorylated channels, after reconstitution into vesicles, displayed a 61% greater Ca-45(2+) uptake, indicating the involvement of tyrosine kinase in EGF-dependent activation of the calcium channel. The results point towards the importance of EGF in the regulation of calcium homeostasis in salivary gland.