The properties of voltage-operated Ca(2+)-channels in bovine isolated trachealis cells.
Freshly-dispersed bovine trachealis cells were used for recording by the patch clamp technique of whole-cell and unitary currents through Ca(2+)-channels. Whole-cell Ca(2+)-current (ICa) activated at -40 mV and appeared to be carried by a single type of Ca(2+)-channel. Inactivation of ICa was increased by increasing the concentration of free Ca2+ within the recording pipette but reduced by using Ba2- as the charge carrier. Steady-state inactivation studies showed that the Ca(2+)-channels were half-maximally available following a conditioning depolarization to -35 mV. A two-pulse protocol showed that ICa induced by the step to a test potential was inversely related to ICa induced by the step to the conditioning potential. Unitary Ba(2+)-currents were activated at a threshold of -30 mV and had a reversal potential of +41 mV. The channel carrying the unitary Ba(2+)-currents had a slope conductance of 23 pS. Steady-state inactivation studies showed that the unitary Ba(2+)-currents were half-maximally available at a holding potential of -28 mV. ICa and unitary Ba(2+)-currents were inhibited by nifedipine (10 nM-1 microM) but augmented by Bay K 8644 (10 microM). It is concluded that the plasmalemma of bovine trachealis muscle contains a single population of voltage-dependent Ca(2+)-channels of the L-type. These channels may be subject to inactivation primarily by an increase in the concentration of free Ca2+ on the cytosolic side of the plasmalemma and secondarily by a voltage-dependent mechanism. Overlap of the inactivation and activation curves of ICa may allow the passage of 'window current' through the Ca(2+)-channels during sustained depolarization.
Green
K A
KA
Department of Physiological Sciences, University of Manchester, UK.
Small
R C
RC
Foster
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RW
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects*; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004095:Dihydropyridines / Q000494:pharmacology; D004594:Electrophysiology; D066298:In Vitro Techniques; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats; D014132:Trachea / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D015220:Calcium Channels; D004095:Dihydropyridines; D001464:Barium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine