Properties of the inactivating outward current in single smooth muscle cells isolated from the rat anococcygeus.
The properties of the voltage- and time-dependent outward current in single smooth muscle cells isolated from the rat anococcygeus were studied. The outward current was activated by depolarizations to membrane potentials positive to -40 mV. Activation followed third order kinetics; at +20 mV, the time for the current to reach half its maximal amplitude was around 55 ms. The current inactivated with a time course that could best be described by a single exponential with a time constant around 1500 ms. The steady-state inactivation curve was voltage dependent over the range -110 to -30 mV, with a half-inactivation point of -67 mV. Recovery from inactivation followed an exponential time course with a time constant of around 770 ms at -90 mV. Deactivating tail current analysis revealed that a 10-fold change in the extracellular potassium ion concentration resulted in a 42 mV change in the reversal potential of the current. The current was blocked by 4-aminopyridine, tetraethylammonium, quinine and verapamil with IC50's--the concentrations producing 50% inhibition of the peak current--of 2 mM, 4 mM, 12 microM and 20 microM respectively. The current was not blocked by Toxin I (100 nM) or glibenclamide (10 microM). The current was still present in cells containing 5 mM EGTA; in these cells, replacing extracellular calcium with cadmium depressed the peak current by around 12%. This could be explained, at least in part, by a negative shift in the voltage dependence of inactivation.
McFadzean
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Division of Biomedical Sciences, King's College London, UK.
England
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D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
D007473:Ion Channels; D015221:Potassium Channels