A calcium-permeable channel activated by muscarinic acetylcholine receptors and InsP3 in developing chick ciliary ganglion neurons

Abstract

The electrical responses elicited by the muscarinic cholinergic pathway have been studied in cultured embryonic chick ciliary ganglion (CG) neurons. Neurons obtained from E7–E8 ganglia were maintained in serum-free medium for 1 to 3 days. Stimulation with 50 μM muscarine induced depolarizing responses in about 30% of the cells tested. In voltage clamp experiments at a holding potential of −50 mV, an inward current could be recorded in the same percentage of cells in response to muscarinic stimulation. In single channel experiments, with standard physiological solution in the pipette, muscarine transiently activated an inward conducting channel. Cell-attached recordings with 100 mM CaCl 2 in the pipette provided evidence that muscarinic agonists can activate a cationic calcium-permeable channel. Two main conductance levels could be detected, of 2.3±0.6 and 5.6±0.6 pS, respectively. In excised patches, addition of 5–20 μM inositol 1,4,5-trisphosphate (InsP 3) to the bath reactivated a channel that could be blocked by heparin and whose characteristics were very similar to those of the channel seen in response to muscarinic stimulation. A channel with similar properties has been previously shown to be activated by basic fibroblast growth factor (bFGF) and InsP 3 in the same preparation.