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 cholinergic agonists on intracellular calcium concentration ([Ca 2 ] i ) in guinea pig VHCs Methods VHCs were isolated from guinea pig crista ampullaris by enzymatic and mechanical methods The effect of cholinergic agonists on [Ca 2 ] i was examined using laser scanning confocal microscopy and the Ca 2 sensitive dye Fluo 3 Results The results showed that the addition of acetylcholine (ACh) and carbachol (CCh), muscarnic and nicotinic agonists, induced [Ca 2 ] i increases in all the VHCs, whereas acetylcholine bromide (ACh Br), a nicotinic agonist, induced the [Ca 2 ] i increase in only a small percentage of VHCs The ACh or CCh induced Ca 2 response could be partially suppressed by atropine In the presence of 0 1?mmol/L atropine, the amplitudes of ACh or CCh induced [Ca 2 ] i responses became significantly smaller than those in atropine free medium ( P <0 01) Conclusions The results suggest the existence of cholinergic receptors in guinea pig VHCs It is the muscarnic agonists rather than nicontic receptors that dominate [Ca 2 ] i variation Atropine can suppress muscarnic agonist induced Ca 2 responses