Cholinergic agonists increase intracellular calcium concentration in guinea pig vestibular hair cells

Objective To better understand the cholinergic receptors in vestibular hair cells (VHC) and their subtypes, and to investigate the effects of choliner gic agonists on intracellular calcium concentration ([Ca2+](i)) in guinea p ig VHCs. Methods VHCs were isolated from guinea pig crista ampullaris by enzymatic a nd mechanical methods. The effect of cholinergic agonists on [Ca2+](i) was examined using laser scanning confocal microscopy and the Ca2+ sensitive dy e Fluo-3. Results The results showed that the addition of acetylcholine (ACh) and car bachol (CCh), muscamic and nicotinic agonists, induced [Ca2+](i) increases in all the VHCs, whereas acetylcholine bromide (ACh-Br), a nicotinic agonis t, induced the [Ca2+](i) increase in only a small percentage of VHCs. The A Ch or CCh-induced Ca2+ response could be partially suppressed by atropine. In the presence of 0.1 mmol/L atropine, the amplitudes of ACh or CCh-induce d [Ca2+](i) responses became significantly smaller than those in atropine f ree medium (P < 0.01). Conclusions The results suggest the existence of cholinergic receptors in g uinea pig VHCs. It is the muscamic agonists rather than nicontic receptors that dominate [Ce2+](i) variation. Atropine can suppress muscamic agonist-i nduced Ce2+ responses.