title: Cholinergic control of membrane conductance and intracellular free Ca2+ in outer hair cells of the guinea pig cochlea.
abstract: We have studied the action of cholinergic agonists on outer hair cells, both in situ and isolated from the cochlea of the guinea pig, combining new fast CCD technology for Ca2+ imaging and conventional patch-clamp methods. Carbachol (1 mM) activated a current with a reversal potential near -70 mV and a bell-shaped I-V curve, suggesting that it was a Ca2+ activated K+ current. In a few cells, this current was preceded by a transient inward current, probably owing to an influx of Ca2+ and other cations through the acetylcholine (ACh) receptors. The amplitude of the Ca2+ signal was maximal in a circumscribed region at the basal pole of the cell and decreased steeply towards the apical pole, compatible with Ca2+ influx and/or Ca2+ induced Ca2+ release at the cells base. The time course of the Ca2+ rise was fastest at the base, but it was still slightly slower, and more rounded, than that of the K+ current. In some recordings the K+ current was observed without any measurable change of intracellular Ca2+. The K+ current was potentiated (18%) by caffeine (5 mM), and decreased (19%) by ryanodine (0.1 mM) in the majority of cells tested. The results are discussed in terms of a labile intracellular Ca2+ store located at the base of the cell, close to the Ca2+ permeable ACh receptor channels and Ca2+ activated K+ channels, whose contribution to the Ca2+ rise occurring in the region of the channels is variable, and probably dependent on its ability to refill with Ca2+.
authors.affiliation: MacKay Institute of Communication and Neuroscience, School of Life Sciences, Keele University, STAFFS, ST5 5BG, UK. M.G.Evans@cns.keele.ac.uk
authors.forename: M G
authors.initials: MG
authors.lastname: Evans
authors.forename: L
authors.initials: L
authors.lastname: Lagostena
authors.forename: P
authors.initials: P
authors.lastname: Darbon
authors.forename: F
authors.initials: F
authors.lastname: Mammano
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology; D002478:Cells, Cultured; D018679:Cholinergic Agonists / Q000494:pharmacology*; D004553:Electric Conductivity; D006168:Guinea Pigs; D018072:Hair Cells, Auditory, Outer / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology; D011978:Receptors, Nicotinic / Q000502:physiology; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects
chemical_list: D002121:Calcium Channel Blockers; D018679:Cholinergic Agonists; D015221:Potassium Channels; D011978:Receptors, Nicotinic; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D002110:Caffeine; D002217:Carbachol; D000109:Acetylcholine; D002118:Calcium