Serotonin, bradykinin and endothelin signalling in a sheep choroid plexus cell line

The secretion of cerebrospinal fluid by the epithelial cells of choroid ple xus is regulated by membrane receptors coupled to adenylyl cyclases or to p hospholipase C. These intracellular signalling pathways as their interactio ns were investigated in a sheep choroid plexus cell line. Endothelin-l, bra dykinin and serotonin induced a transient dose-dependent increase in intrac ellular calcium. EC 50 were 10(-8)M for endothelin-l, 10(-8) M for bradykin in and 10(-6) M for serotonin. Maximal increase in intracellular calcium wa s comparable for bradykinin and serotonin, but was 3 to 5 fold larger for e ndothelin-l. Successive stimulations with endothelin-1, serotonin or bradyk inin elicited calcium increases similar to single stimulations reflecting a bsence of heterologous desensitization between these receptors. Forskolin-i nduced cAMP accumulation was potentiated by bradykinin, but not by serotoni n and endothelin-l. This potentiation resulted from an increase in cAMP pro duction rather than to an inhibition of cAMP hydrolysis. These data suggest that serotonin, endothelin-l and bradykinin each use specific signalling p athways in the sheep choroid plexus cells.