title: Mechanism and metabolic disposition of verapamil-evoked overflow of radioactivity from isolated atria preloaded with [3H]norepinephrine.
abstract: In this study the mechanism and metabolic profile of verapamil-evoked release of radioactivity was investigated in the rat isolated atria preloaded with [3H]norepinephrine [( 3H]NE). Verapamil (10(-7) to 10(-3) M) caused a dose-related increase in the outflow (or the fractional release) of 3H. The fractional 3H-release produced by verapamil was reduced markedly in tissues which had been preloaded with [3H]NE in the presence of cocaine (10 microM) or after pretreatment of animals with reserpine (5 mg/kg i.p., 24 hr before sacrifice). Verapamil-evoked fractional 3H-release was unchanged in the presence of tetrodotoxin (5 X 10(-6) M) or in Ca++-free Krebs' medium containing 2 mM ethylene glycol bis(beta-aminoethyl ether)N,N'-tetraacetic acid. Whereas greater than 90% of tissue 3H-content consisted of unchanged [3H]NE, 60 to 75% of the spontaneous outflow and the verapamil-evoked overflow consisted of [3H]-3,4-dihydroxyphenylglycol and 2 to 10% was unchanged [3H]NE. When both cocaine (10 microM) and hydrocortisone (28 microM) (uptake-1 and uptake-2 blockers, respectively) were present, although the spontaneous outflow, as well as verapamil-evoked overflow, of radioactivity was increased, the metabolic profiles remained essentially unchanged. The addition of pargyline (10 microM), a monoamine oxidase inhibitor, in addition to the uptake-1 and uptake-2 blockers to the Krebs' solution significantly depressed both the spontaneous outflow and verapamil-evoked overflow of 3H; the verapamil-evoked overflow under this condition, however, consisted of unchanged [3H]NE (greater than 90%).(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D003042:Cocaine / Q000494:pharmacology; D006325:Heart Atria / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D010293:Pargyline / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012110:Reserpine / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014700:Verapamil / Q000037:antagonists & inhibitors / Q000494:pharmacology*
chemical_list: D013779:Tetrodotoxin; D012110:Reserpine; D010293:Pargyline; D014700:Verapamil; D003042:Cocaine; D002118:Calcium; D009638:Norepinephrine