CYTOSKELETAL INHIBITORS IMPAIR CA2-Y AND OTHER G(I)-COUPLED RECEPTORS( ELEVATIONS VIA NEUROPEPTIDE)

Neuropeptide Y, alpha(2)-adrenoceptors, thrombin and certain muscarini c acetylcholine receptors can couple to elevations of intracellular fr ee Ca2+ concentrations via G(i)-proteins. We have studied the effects of inhibitors of microtubules (colchicine, nocodazole, vinblastine) an d microfilaments (cytochalasin B, cytochalasin D) on these effects in human erythroleukemia (HEL) cells. Both types of inhibitors reduced ne uropeptide Y-, adrenaline- (via alpha(2A)-adrenoceptors) and thrombin- stimulated Ca2+ elevations while the inactive analog beta-lumicolchici ne was without inhibitory effects. Similarly, in SK-N-MC cells vinblas tine inhibited neuropeptide Y and carbachol (via muscarinic receptors) stimulated Ca2+ elevations. In HEL cells the inhibitory effects of th e microfilament inhibitor cytochalasin D and the microtubule inhibitor colchicine were not additive. Colchicine, nocodazole or cytochalasin D did not affect the binding of the agonist neuropeptide Y. On the oth er hand, neuropeptide Y and thrombin significantly stimulated GTP gamm a S binding in the absence but not in the presence of colchicine, vinb lastine or cytochalasin B. This was not due to sequestration of G-prot ein alpha-subunits, since nocodazole did not affect the distribution o f immunodetectable G(i alpha 1/2) or G(i alpha 3) between membrane and cytosolic fractions. We conclude that disruption of microfilaments or microtubules impairs Ca2+ elevations by neuropeptide Y and other G(i) -coupled receptors by inhibiting receptor/G(i)-protein interaction; th is does not involve impairment of agonist binding to the receptor or r edistribution of G(i)-protein alpha-subunits.