Mechanism of acetylcholine-induced calcium signaling during neuronal differentiation of P19 embryonal carcinoma cells in vitro

Muscarinic (mAChRs) and nicotinic acetylcholine receptors (nAChRs) are involved in various physiological processes, including neuronal development. We provide evidence for expression of functional nicotinic and muscarinic receptors during differentiation of P19 carcinoma embryonic cells, as an in vitro model of early neurogenesis. We have detected expression and activity of α2-α7, β2, β4 nAChR and M1-M5 mAChR subtypes during neuronal differentiation. Nicotinic α3 and β2 mRNA transcription was induced by addition of retinoic acid to P19 cells. Gene expression of α2, α4-α7, β4 nAChR subunits decreased during initial differentiation and increased again when P19 cells underwent final maturation. Receptor response in terms of nicotinic agonist-evoked Ca2+ flux was observed in embryonic and neuronal-differentiated cells. Muscarinic receptor response, merely present in undifferentiated P19 cells, increased during neuronal differentiation. The nAChR-induced elevation of intracellular calcium ([Ca2+]i) response in undifferentiated cells was due to Ca2+ influx. In differentiated P19 neurons the nAChR-induced [Ca2+]i response was reduced following pretreatment with ryanodine, while the mAChR-induced response was unaffected indicating the contribution of Ca2+ release from ryanodine-sensitive stores to nAChR- but not mAChR-mediated Ca2+ responses. The presence of functional nAChRs in embryonic cells suggests that these receptors are involved in triggering Ca2+ waves during initial neuronal differentiation.