Abstract

Endothelin (ET)-1, -2, -3, big ET-1 and sarafotoxin S6b (S6b) dose-dependently increased phosphoinositide (PI) hydrolysis by 6- to 10-fold in cultured cerebellar granule cells prelabeled with [3H] myoinositol. The PI response elicited by ET-1 was dependent on the presence of extracellular Ca++, but was not reduced by organic (nisoldipine, nimodipine) or inorganic (Co++, Mn++) calcium channel blockers. Pretreatment of granule cells with tetrodotoxin or amiloride failed to affect the response to ET-1. Extracellular sodium depletion resulted in a marked increase in basal PI turnover; however, the net increase of PI turnover induced by ET-1 was unchanged. ET-induced PI breakdown could be partially inhibited by short or long term treatment with phorbol dibutyrate but was unaffected by pertussis toxin. ET- and S6b-induced PI turnover were dependent on the culturing time of granule cells, with the maximal response in a 4-day culture. The ET- and S6b-induced PI turnover appeared to be additive to that induced by carbachol, histamine, norepinephrine, serotonin, glutamate and maitotoxin. However, the responses induced by ET and S6b were nonadditive. Prestimulation of cells with ET or S6b for 30 sec to 24 hr resulted in dramatic loss of the ability of ET and S6b to stimulate PI hydrolysis, without affecting subsequent responsiveness induced by other stimuli, indicating homologous desensitization for ET- and S6b-induced responses. Moreover, our results further support the notion that ET and S6b act on the same population of receptors in cerebellar granule cells.