Norepinephrine inhibits calcium action potential through alpha 2-adrenoceptors in rabbit vesical parasympathetic neurons.
Intracellular and voltage-clamp recordings were made from neurons in rabbit vesical parasympathetic ganglia (VPG) maintained in vitro. Norepinephrine (NE, 10 nM-10 microM) reduced the Ca2+ component of the action potential and the afterhyperpolarization. Clonidine and UK14304, the selective alpha 2-adrenoceptor agonists, mimicked the inhibitory effects of NE on the action potential. NE and UK14304 blocked the Ca2+ spike elicited in the presence of tetrodotoxin and tetraethylammonium. UK14304 suppressed the inward Ca2+ current induced by depolarizing step command under the voltage-clamp condition. These inhibitory actions were antagonized by yohimbine and idazoxan but not by prazosin and propranolol. It is suggested that alpha 2-adrenoceptors mediate the inhibition of voltage-dependent Ca2+ entry during the action potential.
Akasu
T
T
Department of Physiology, Kurume University School of Medicine, Japan.
Tsurusaki
M
M
Nishimura
T
T
Tokimasa
T
T
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D000068438:Brimonidine Tartrate; D002118:Calcium / Q000502:physiology*; D003000:Clonidine / Q000494:pharmacology; D005726:Ganglia, Parasympathetic / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology*; D011810:Quinoxalines / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D001743:Urinary Bladder / Q000294:innervation*; D015016:Yohimbine / Q000494:pharmacology
D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D003000:Clonidine; D002118:Calcium; D009638:Norepinephrine