K+ currents activated by depolarization in cardiac fibroblasts.
K(+) currents expressed in freshly dispersed rat ventricular fibroblasts have been studied using whole-cell patch-clamp recordings. Depolarizing voltage steps from a holding potential of -90 mV activated time- and voltage-dependent outward currents at membrane potentials positive to approximately -30 mV. The relatively slow activation kinetics exhibited strong dependence on the membrane potential. Selected changes in extracellular K(+) concentration ([K(+)](o)) revealed that the reversal potentials of the tail currents changed as expected for a K(+) equilibrium potential. The activation and inactivation kinetics of this K(+) current, as well as its recovery from inactivation, were well-fitted by single exponential functions. The steady-state inactivation was well described by a Boltzmann function with a half-maximal inactivation potential (V(0.5)) of -24 mV. Increasing [K(+)](o) (from 5 to 100 mM) shifted this V(0.5) in the hyperpolarizing direction by -11 mV. Inactivation was slowed by increasing [K(+)](o) to 100 mM, and the rate of recovery from inactivation was decreased after increasing [K(+)](o). Block of this K(+) current by extracellular tetraethylammonium also slowed inactivation. These [K(+)](o)-induced changes and tetraethylammonium effects suggest an important role for a C-type inactivation mechanism. This K(+) current was sensitive to dendrotoxin-I (100 nM) and rTityustoxin Kalpha (50 nM).
Shibukawa
Yoshiyuki
Y
Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, Alberta, Canada.
Chilton
E Lisa
EL
Maccannell
K Andrew
KA
Clark
Robert B
RB
Giles
Wayne R
WR
D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D005347:Fibroblasts / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D015221:Potassium Channels