Roles of outward potassium currents in the action potentials of guinea pig ureteral myocytes.
Outward currents of freshly dissociated ureteral myocytes consist mainly of Ca(2+)-activated K+ current (IKCa) and a transient outward current (ITO). No delayed rectifier current was apparent. IKCa is small and nondecaying and fluctuates actively and irregularly. Blocking IKCa decreased resting membrane conductance and prolonged action potential plateaus, showing its roles in maintaining the resting potential and in repolarizing action potentials. It is also responsible for the membrane potential fluctuations on action potential plateaus. Neither 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride nor caffeine reduced the fluctuations in the outward current or in the action potentials, indicating that internal Ca2+ storage contributes little to the fluctuations. ITO has fast activation and inactivation kinetics with inactivation time constants of approximately 15 and 150 ms, respectively. Its highly negative voltage-availability relationship (V0.5 = -70.5 mV) suggests a low availability (< 5%) at normal resting potentials. It has only trivial effects on action potentials.
Sui
J L
JL
Department of Pharmacology, State University of New York Health Science Center at Brooklyn 11203, USA.
Kao
C Y
CY
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D018999:Charybdotoxin / Q000494:pharmacology; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013997:Time Factors; D014513:Ureter / Q000502:physiology*
D002121:Calcium Channel Blockers; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D018999:Charybdotoxin; D002110:Caffeine; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D019789:Tetraethylammonium; D002118:Calcium