Role of the proton electrochemical gradient in monoamine transport by bovine chromaffin granules

Abstract

The role of the transmembrane potential (Δψ), the proton concentration gradient (ΔpH) and the proton electrochemical gradient (Δμ H +) in monoamine uptake by bovine chromaffin granules or ghosts was investigated. In presence of ATP the permeant anion SCN − collapsed the Δψ (inside positive) and inhibited monoamine uptake by granules or well buffered ghosts. With lightly buffered ghosts, SCN − induced an acidification which resulted in a low inhibition of uptake. Cation efflux as well as anion influx affected the Δψ, and a transient valinomycin-mediated K + efflux induced a lag in the uptake. The ΔpH-driven noradrenalin uptake was also sensitive to Δψ, since superimposing a positive or a negative Δψ to the ΔpH, respectively, increased or decreased the rate of noradrenalin accumulation. A ΔpH was required for this increase of uptake rate, which was proportional to the Δψ. The pH-dependence of the ATP-induced monoamine uptake by granules pointed to the Δμ H + as the driving force. In contrast with the rate of uptake, which was not dependent on the anions present, the extent of amine incorporation was decreased when the internal anionic buffer concentration was decreased and, at a low internal buffer concentration, when ATP anion transport was blocked.