Developmental changes in calcium current pharmacology and somatostatin inhibition in chick parasympathetic neurons

Abstract

Voltage-dependent calcium (Ca2+) currents were characterized and modulatory effects of somatostatin were measured in acutely dissociated chick ciliary ganglion neurons at embryonic stages 34, 37, and 40. This developmental time period coincides with the period of synapse formation between ciliary ganglion neurons and peripheral eye muscles. At all three developmental stages Ca2+ current could be blocked almost completely by combined application of ω-CgTX GVIA and nitrendipine. At young embryonic ages there was significant overlap in sensitivity, with ~75% of the current sensitive to either blocker applied independently. By stage 40, there was very little or no overlap in sensitivity, with ~75% of the current blocked by ω-CgTX GVIA (N-type) and 30% blocked by nitrendipine (L-type). These data are consistent with earlier findings that the pharmacology of acetylcholine release from ciliary ganglion nerve terminals changes during development from sensitivity to both dihydropyridines and ω-CgTX GVIA to selective sensitivity to ω-CgTX GVIA (Gray et al., 1992). Somatostatin reduced Ca2+ current by 50-60% at all three developmental stages. At early developmental stages somatostatin receptors coupled predominantly to the current that was sensitive to both ω-CgTX GVIA and nitrendipine. By stage 40, somatostatin primarily inhibited classically defined N-type current (selectively sensitive to ω-CgTX GVIA). Thus, somatostatin receptor coupling to Ca2+ channels persisted throughout development as Ca2+ current pharmacology changed.