Muscarinic receptor subtypes mediate stimulatory and paradoxical inhibitory effects on an insulin-secreting beta cell line

Acetylcholine (ACh), a major neurotransmitter from the autonomic nervous system, regulates the cholinergic stimulation of insulin secretion, through interactions with muscarinic receptors. The present study has characterised the individual involvement of muscarinic receptor subtypes in ACh-induced insulin secretion, using clonal P cells and selective muscarinic receptor antagonists. BRIN BD11 cells clearly expressed mRNA encoding m1-m4 whereas m5 was not detected by RT-PCR. Insulin release was measured from BRIN BD11 cells treated with ACh in the presence of muscarinic receptor antagonists at concentrations ranging from 3 nM to 1 muM. 300 nM of muscarinic toxin-3 (M4 antagonist) and 1 muM of methoctramine (M2 antagonist) increased ACh (100 muM) stimulated insulin secretion by 168% and 50% respectively (ANOVA, P