title: Activation of non-selective cation conductance by carbachol in freshly isolated bovine ciliary muscle cells.
abstract: In smooth muscle cells freshly isolated from the bovine ciliary body, effects of carbachol (CCh) on the membrane potential and current were examined by the whole-cell clamp method. The resting membrane potential of the muscle cells used was -60 +/- 1 mV (n = 111). Extracellular application of CCh (2 microM) depolarized the cells to -15 +/- 5 mV (n = 50) with an apparent increase in membrane conductance. Under voltage-clamp conditions, CCh (2 microM) evoked an inward current which exhibited inward-going rectification and reversed the polarity at about 0 mV. Removal of Na+ from the external solution caused a reduction of the amplitude of the current and a shift of the reversal potential to the negative direction. CCh was able to elicit an inward current even under a condition where Ca2+ was the only cation producing an inwardly directed electrochemical gradient. The current was not affected by verapamil or by tetrodotoxin. The CCh-induced current was inhibited by antimuscarinic agents with the affinity sequence: atropine approximately 4-DAMP > > pirenzepine > AF-DX116, indicating that the response is mediated by a muscarinic cholinoceptor that belongs to the M3-subtype. Unlike the non-selective cation channel current in intestinal smooth muscles, which is activated by elevation of the intracellular Ca2+ concentration ([Ca2+]i), the current of the ciliary muscle was inactivated when the [Ca2+]i was increased. The conductance, which admits Ca2+, may serve as a pathway for Ca2+ entry required for contraction.
authors.affiliation: Department of Ophthalmology, School of Medicine, Nagoya University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Takai
authors.forename: S
authors.initials: S
authors.lastname: Awaya
authors.forename: A
authors.initials: A
authors.lastname: Takai
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology*; D002412:Cations / Q000378:metabolism*; D002417:Cattle; D002924:Ciliary Body / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004594:Electrophysiology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018721:Muscarinic Agonists / Q000494:pharmacology*; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques
chemical_list: D002412:Cations; D007473:Ion Channels; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D002217:Carbachol; D002118:Calcium