Effects of calcium channel antagonists on the depolarization-evoked release of norepinephrine in the rabbit iris-ciliary body.
The effects of several representative calcium channel antagonists on depolarization-evoked release of [3H]-norepinephrine were investigated in isolated, superfused rabbit iris-ciliary bodies. Potassium (50 mM)-evoked neurosecretion was blocked by 5 mM CoCl2 and partially inhibited by 10(-6) M nitrendipine or verapamil. Electrically-evoked neurosecretion was similarly blocked by CoCl2, but was unaffected by nitrendipine or verapamil. It is concluded from these results that sympathetic terminals in the rabbit iris-ciliary body contain dihydropyridine- and verapamil-sensitive calcium channels which contribute, under conditions of prolonged depolarization, to neurotransmitter release.
Jumblatt
J E
JE
Department of Ophthalmology, University of Louisville School of Medicine, KY 40202.
D000200:Action Potentials / Q000187:drug effects; D000320:Adrenergic Fibers / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002924:Ciliary Body / Q000187:drug effects / Q000294:innervation* / Q000378:metabolism; D003035:Cobalt / Q000494:pharmacology; D066298:In Vitro Techniques; D007498:Iris / Q000187:drug effects / Q000294:innervation* / Q000378:metabolism; D009568:Nitrendipine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D003035:Cobalt; D009568:Nitrendipine; D014700:Verapamil; D011188:Potassium; D009638:Norepinephrine