Acetylcholine increases intracellular Ca2+ concentration and hyperpolarizes the guinea-pig outer hair cell.
Extracellularly applied acetylcholine (ACh) induced outward currents in isolated outer hair cells of a guinea-pig cochlea. The ACh induced current was carried by K+ ions. The current amplitude was ACh dose dependent with a KD of 12 microM. The ACh induced outward current was reversibly blocked by extracellularly applied atropine (1 microM), d-tubocurarine (d-TC, 1 microM), apamin (1 microM) and strychnine (0.1-10 microM). D-TC (10 microM) not only blocked the ACh induced outward current, but also reduced the amplitude of depolarization induced outward current. ACh induced a rise of intracellular Ca2+ concentration ([Ca2+]i). D-TC (10 microM) reduced but did not totally block the increase of [Ca2+]i. In a low Ca2+ (0.1 mM) extracellular medium, the amplitude of ACh induced current was reduced rapidly and was recovered gradually to the normal level after the extracellular Ca2+ concentration was resumed. It is probable that ACh hyperpolarizes the guinea-pig outer hair cell membrane by activation of a Ca(2+)-activated K+ conductance.
Doi
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National Institute for Physiological Science, Okazaki, Japan.
Ohmori
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D000109:Acetylcholine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D006168:Guinea Pigs; D006198:Hair Cells, Auditory / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D010276:Parasympatholytics / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D013331:Strychnine / Q000494:pharmacology; D014403:Tubocurarine / Q000494:pharmacology
D010276:Parasympatholytics; D001030:Apamin; D013331:Strychnine; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium; D014403:Tubocurarine