Effects of cholinergic agonist on intracellular calcium concentration of isolated vestibular hair cells in guinea pigs

Objective In order to understanding the Cholinergic receptors and its subtype, the desensitization of receptors, the effects of cholinergic agonist on intracellular calcium concentration （Ca²⁺i） of isolated VHCs from the guinea pig were investigated. Methods: Vestibular hair cells （VHC） were isolated from guinea pig crista ampullaris by enzymatic and mechanical methods The influence of cholinergic agonist on Ca²⁺ i was examined using laser scanning confocal microscopy（LSCM） and the Ca²⁺ sensitive dye Fluo-3. Results: ①Different concentration of acetylcholine（ACh） and carbachol（CCh）, a muscarnic and nicotinic agonist, induced Ca²⁺i increase with distinctive extent in all VHCs. However, acetycholine Bromide（ACh-Br）, a nicotinic agonist, induced i responses only in some （4/5） of VHCs when 10mmol/L of ACh-Br was applied. No significant Ca²⁺i increase was observed when 1mmol/L of ACh-Br was applied②The desensitization of VHCs was observed when ACh or CCh successively applying to a VHC. In contrast, different type agonist successively applying to VHCs could prevent the desensitization. ③The ACh or CCh induced Ca²⁺ response was suppressed by atropine. In the presence of 0.1mmol/L atropine, the amplitudes of ACh or CCh induced Ca²⁺ response became smaller than that in atropine free medium There is a statistical difference （P＜0.01） Conclusion: The results indicated the presence of cholinergic receptor on guinea pig VHCs. Muscarnic agonist was more responsive for i variation than nicontic receptors. Atropine can suppress muscarnic agonist,induced Ca²⁺ responses. The desensitization of muscarnic receptors to successive stimulations was significant.