Different Calcium Channels Mediate Basal and Stimulated MSH Secretion

Signature Grand, Davie, Florida, USA

Objective. We investigated the types of calcium channels involved in basal and K-stimulated MSH secretion. Background. Both basal and K-stimulated secretion of melanophore-stimulating hormone (MSH) from neurointermediate lobes (NILs) of the anole are Ca dependent. Nimodipine and BAY K 8644, which block and potentiate, respectively, Ca influx through L-type Ca channels, block and potentiate, respectively, K-stimulated MSH secretion but have no effect on basal secretion. These observations suggest that K-stimulated MSH secretion is mediated by Ca influx through L-type Ca channels whereas basal secretion is not. We further investigated the Ca channels involved in both basal and K-stimulated MSH secretion using toxins which preferentially block different types of Ca channels. Methods. Anole NILs were placed in a perifusion chamber and the MSH content of the perifusate was measured using the Anolis skin bioassay. None of the toxins affected the assay. Results. sFTX-3.3 a blocker of P/Q and T-type Ca channels, inhibited basal but not K-stimulated secretion. Agatoxin, a selective P/Q-type Ca channel blocker, had no effect on either basal or K-stimulated secretion suggesting that the block of basal secretion by sFTX-3.3 was due to its effects on T-type channels. The L-type Ca channel blocker FS-2, behaved like nimodipine and suppressed K-stimulated secretion but not basal secretion. A selective N-type Ca channel blocker, ω-conotoxin GVIA, had no effect on either K-stimulated or basal secretion. Conclusion. These results indicate that basal and K-stimulated secretion are mediated by Ca influx through different Ca channels: basal through T-type and K-stimulated through L-type Ca channels. Grants. This study was supported by a NSU-HPD Research Award.