title: Voltage-dependent calcium current in dissociated smooth muscle cells of the buccal mass of Aplysia.
abstract: Isolated smooth muscle cells of the buccal mass of Aplysia contracted in response to depolarization elicited by a patch electrode in whole-cell configuration. With cesium-containing pipet solution and tetraethylammonium and 4-aminopyridine in the external solution depolarization elicited inward current. The voltage-dependent inward current was blocked completely by lanthanum (10 mmol.l-1), inhibited 80-90% by nifedipine (1 mumol.l-1), and was dependent upon extracellular calcium. These results showed that the voltage-dependent inward current was due to activation of voltage-dependent calcium channels (VDCaCH). Minimal depolarization to begin activating VDCaCH was -60 to -30 mV. Inward current peaked within 8 ms and then decreased rapidly to a lower level of relatively non-inactivating current. The initial peak current could be mostly inactivated by a depolarization to -20 mV for 500 ms. Nifedipine reduced both the peak current and the relatively non-inactivating current. Nifedipine inhibited high potassium-elicited contractions of both intact and dissociated muscle. These results suggested that VDCaCH mediates calcium influx which triggers contraction in molluscan smooth muscle fibers.
authors.affiliation: Department of Physiology, Wayne State University, Detroit, MI 48201.
authors.forename: J L
authors.initials: JL
authors.lastname: Ram
authors.forename: L X
authors.initials: LX
authors.lastname: Liu
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001048:Aplysia / Q000502:physiology*; D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000493:pharmacokinetics*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002469:Cell Separation; D002586:Cesium / Q000494:pharmacology; D004558:Electric Stimulation; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology* / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D013757:Tetraethylammonium Compounds; D002586:Cesium; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D009543:Nifedipine; D002118:Calcium