Examination of the role of calcium in the adrenaline-induced hyperpolarization of bullfrog sympathetic neurons.
The adrenaline-induced hyperpolarization, which was recorded in neurons of bullfrog paravertebral sympathetic ganglia by means of the sucrose gap technique, was antagonized by 1 mM 4-aminopyridine. The response was unaffected by drugs which influence intracellular Ca2+ movements or Ca2+-sensitive K+ conductances, i.e. 100 or 200 microM Cd2+, 60 microM dantrolene Na+, 10 mM tetraethylammonium bromide, 0.5-2.0 microM apamin or 70 microM (+)-tubocurarine chloride. The spontaneous, rhythmic hyperpolarizations which occur in ganglionic neurons in the presence of 5 mM caffeine and reflect activation of Ca2+-sensitive K+ conductances following mobilization of intracellular Ca2+, were examined by means of intracellular recording. These responses were often biphasic, comprising a transient rapid early phase and a slow late phase. Tetraethylammonium (10 mM) and 0.5-2.0 microM apamin antagonized the rapid early phase and 70 microM (+)-tubocurarine chloride antagonized both phases of the response. Neither phase of these spontaneous, rhythmic, caffeine-induced hyperpolarizations were affected by 1 mM 4-aminopyridine. Although the adrenaline-induced hyperpolarization was antagonized by 50 microM 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate and by 50 microM quinidine, the majority of the results argue against the hypothesis that mobilization of intracellular Ca2+ is required for activation of the K+ conductance thought to underlie the adrenaline-induced hyperpolarization.
Rafuse
P E
PE
Department of Pharmacology, University of Alberta, Edmonton, Canada.
Smith
P A
PA
Zidichouski
J A
JA
D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002025:Bufonidae; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D003620:Dantrolene / Q000494:pharmacology; D004594:Electrophysiology; D004837:Epinephrine / Q000494:pharmacology*; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D011802:Quinidine / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects*; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014403:Tubocurarine / Q000494:pharmacology
D000631:Aminopyridines; D013757:Tetraethylammonium Compounds; D001030:Apamin; D002110:Caffeine; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D015761:4-Aminopyridine; D003620:Dantrolene; D011802:Quinidine; D011188:Potassium; D002118:Calcium; D014403:Tubocurarine; D004837:Epinephrine