Muscarinic receptors modulate intacellular calcium level in chick sensory neurons

In the present work we have studied the variation of intracellular calcium levels induced by muscarinic agonists in chick dorsal root ganglia neurons. Muscarinic agonists such as muscarine and oxotremorine cause an increase of intracellular calcium levels in fura-2AM-loaded DRG neurons of E18 chick embryos. This increase was abolished following treatment with 1 μM atropine but not by 1 μM mecamylamine, indicating that the observed intracellular calcium increase, was dependent on muscarinic receptor activation. Stimulation in absence of external calcium or pre-incubation of the DRG cultures with thapsigargin or Mn2+ demonstrated that [Ca2+]i increase is mainly due to its release from intracellular stores. The use of selective antagonists of muscarinic receptor subtypes also indicated that M1 and to a lesser extent M3 receptor subtypes are responsible for the observed intracellular calcium mobilization. Finally pre-treatment of DRG cultures with pertussis toxin showed that the variation of [Ca2+]i levels was dependent on PTX-insensitive G-protein. Moreover muscarinic agonists induce in DRG also the increase of IPs level, suggesting that the variations of intracellular calcium levels may be due at least in part to the activation of the phosphoinositide transduction pathway. In conclusion the reported observations demonstrate the activity of muscarinic receptors in sensory neurons, suggesting a functional role for acetylcholine in sensory transduction.