5-HYDROXYTRYPTAMINE(2A) RECEPTORS ON CULTURED RAT SCHWANN-CELLS

Intracellular calcium responses of cultured rat Schwann cells to 5-hyd roxytryptamine (5-HT) were examined using the calcium indicator dye fl uo-3. Consistent changes in [Ca2+](i) were observed with bath applicat ion of 5-HT and the basis of these responses was characterized. Applic ation of 5-HT elicited a transient increase in intracellular calcium i n a subpopulation of cultured Schwann cells. In many responding cells, the response recurred at approximately regular intervals following th e initial transient. In some cases, these oscillations lasted for hour s following removal of 5-HT from the bath. The increase in intracellul ar calcium evoked by 5-HT still occurred in the absence of extracellul ar calcium, suggesting that 5-HT induces calcium release from intracel lular stores. Consistent with this hypothesis, the response to 5-HT wa s prevented by depletion of inositol trisphosphate-sensitive intracell ular calcium stores with thapsigargin. Bath application of caffeine, k nown to activate Ca2+ release from ryanodine receptor-mediated stores, did not elicit an increase in [Ca2+](i). These results also suggested that 5-HT acted by stimulating a member of the 5-HT2 receptor family since this family employs inositol trisphosphate as a second messenger . In agreement with this interpretation, it was found that the 5-HT-in duced intracellular calcium transients could be reversibly blocked by both ketanserin and spiperone, suggesting that the transients are medi ated by 5-HT2A receptors. Additional support for this conclusion was o btained by immunocytochemistry using an anti-idiotypic antibody that r ecognizes a subset of 5-HT receptors. (C) 1996 Wiley-Liss, Inc.