Role of a transmembrane pH gradient in epinephrine transport by chromaffin granule membrane vesicles.
ATP-driven transport and accumulation of epinephrine in chromaffin granule membrane vesicles isolated from bovine adrenal medulla is inhibited by the proton ionophores carbonylcyanide p-trifluoromethoxyphenylhydrazone and nigericin, but not by valinomycin. Moreover, an artificially imposed pH gradient (interior acid) is able to drive this reserpine-sensitive transport system in the absence of ATP. Dicyclohexylcarbodiimide, an inactivator of the chromaffin granule membrane-bound ATPase, completely inhibits ATP-dependent epinephrine accumulation, but has much less effect when an imposed pH gradient is the driving force for epinephrine transport. The findings provide a strong indication that a pH gradient (interior acid) is the immediate driving force for epinephrine uptake in these storage granules and suggest that ATP-driven epinephrine transport is the result of two processes: (i) generation of a proton electrochemical gradient (interior acid and positive) by the membrane-bound, proton-translocating ATPase; and (ii) pH gradient-driven accumulation of the catecholamine.
D000818:Animals; D001693:Biological Transport, Active; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002417:Cattle; D002837:Chromaffin Granules / Q000378:metabolism*; D002838:Chromaffin System / Q000378:metabolism*; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004837:Epinephrine / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D007476:Ionophores; D009550:Nigericin / Q000494:pharmacology; D012110:Reserpine / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
D007476:Ionophores; D014634:Valinomycin; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D004024:Dicyclohexylcarbodiimide; D012110:Reserpine; D009550:Nigericin; D004837:Epinephrine