Muscarinic receptors modulate intracellular calcium level in chick sensoryneurons

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 o f intracellular calcium levels in fura-2AM-loaded DRG neurons of E18 chick embryos. This increase was abolished following treatment with 1 mu M atropi ne but not by 1 mu M mecamylamine, indicating that the observed intracellul ar calcium increase, was dependent on muscarinic receptor activation. Stimu lation in absence of external calcium or pre-incubation of the DRG cultures with thapsigargin or Mn2+ demonstrated that [Ca2+](i) increase is mainly d ue to its release from intracellular stores. The use of selective antagonis ts of muscarinic receptor subtypes also indicated that M-1 and to a lesser extent M-3 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-i nsensitive G-protein. Moreover muscarinic agonists induce in DRG also the i ncrease of IPs level, suggesting that the variations of intracellular calci um levels may be due at least in part to the activation of the phosphoinosi tide transduction pathway. In conclusion the reported observations demonstr ate the activity of muscarinic receptors in sensory neurons, suggesting a f unctional role for acetylcholine in sensory transduction. (C) 2000 Elsevier Science B.V. All rights reserved.