5-Hydroxytryptamine2A receptors on cultured rat Schwann cells

Intracellular calcium responses of cultured rat Schwann cells to 5-hydroxytryptamine (5-HT) were examined using the calcium indicator dye fluo-3. Consistent changes in [Ca2+]i were observed with bath application of 5-HT and the basis of these responses was characterized. Application of 5-HT elicited a transient increase in intracellular calcium in a subpopulation of cultured Schwann cells. In many responding cells, the response recurred at approximately regular intervals following the initial transient. In some cases, these oscillations lasted for hours following removal of 5-HT from the bath. The increase in intracellular calcium evoked by 5-HT still occurred in the absence of extracellular calcium, suggesting that 5-HT induces calcium release from intracellular stores. Consistent with this hypothesis, the response to 5-HT was prevented by depletion of inositol trisphosphate-sensitive intracellular calcium stores with thapsigargin. Bath application of caffeine, known 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-induced intracellular calcium transients could be reversibly blocked by both ketanserin and spiperone, suggesting that the transients are mediated by 5-HT2A receptors. Additional support for this conclusion was obtained by immunocytochemistry using an anti-idiotypic antibody that recognizes a subset of 5-HT receptors.