title: A fast transient outward monovalent current in rat saphenous myocytes passing through Ca2+ channels.
abstract: Transient outward currents in rat saphenous arterial myocytes were studied using the perforated configuration of the patch-clamp method. When myocytes were bathed in a Na-gluconate solution containing TEA to block large-conductance Ca2+-activated K+ (BK) currents, depolarizing pulses positive to +20 mV from a holding potential of -100 mV induced fast transient outward currents. The activation and inactivation time constants of the current were voltage dependent, and at +40 mV were 3.6 +/- 0.8 ms and 23.9 +/- 6.4 ms (n = 4), respectively. The steady-state inactivation of the transient outward current was steeply voltage dependent (z = 1.7), with 50% of the current inactivated at -55 mV. The current was insensitive to the A-type K+ channel blocker 4-AP (1-5 mM), and was modulated by external Ca, decreasing to approximately 0.85 of control values upon raising Ca2+ from 1 to 10 mM, and increasing approximately 3-fold upon lowering it to 0.1 mM. Transient outward currents were also recorded following replacement of internal K+ with either Na+ or Cs+, raising the possibility that the current was carried by monovalent ions passing through voltage-gated Ca2+ channels. This hypothesis was supported by the finding that the transient outward current had the same inactivation rate as the inward Ba2+ current, and that both currents were effectively blocked by the L-type Ca2+ channel blocker, nifedipine and enhanced by the agonist BAYK8644.
authors.affiliation: Dipartimento Biologia Cellulare e Molecolare, Universita' di Perugia, Via Pascoli 1, I-06100 Perugia, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Catacuzzeno
authors.forename: A A
authors.initials: AA
authors.lastname: Harper
authors.forename: B
authors.initials: B
authors.lastname: Fioretti
authors.forename: F
authors.initials: F
authors.lastname: Franciolini
mesh_terms: D000818:Animals; D001158:Arteries / Q000503:physiopathology; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004594:Electrophysiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012501:Saphenous Vein; D012680:Sensitivity and Specificity
chemical_list: D015220:Calcium Channels; D002118:Calcium