Characteristics of endothelin-1 and endothelin-3 stimulation of phosphoinositide breakdown differ between regions of guinea-pig and rat brain.

Endothelin-3 was almost equipotent with endothelin-1 (ET-1) in stimulating phosphoinositide hydrolysis, as indicated by [3H]inositol phosphate formation, in cross-chopped slices of guinea-pig cerebellum, rat cerebellum and rat cerebral cortex. The magnitude of [3H]inositol phosphate formation was greatest in guinea-pig cerebellum, approximately 10-fold over basal levels. The similar level of [3H]IP1 accumulation produced by 1 mumol.l-1 ET-1 in rat cerebellum and cerebral cortex (circa 3-fold over basal) did not mirror the large difference in high-affinity [125I]ET-1 binding sites in the two regions. Moreover, the EC50 for ET-induced [3H]IP1 formation differed markedly between the three tissues (7 +/- 2 nmol.l-1 in rat cerebral cortex, 65 +/- 15 nmol.l-1 in guinea-pig cerebellum and greater than 200 nmol.l-1 in rat cerebellum). Only in rat cerebral cortex was the EC50 of the same order as has been reported for peripheral responses to ET-1.