Mechanisms of proton-linked monoamine transport in chromaffin granule ghosts

In bovine chromaffin granules, an inwardly directed H+-translocating ATPase can create either a transmembrane pH gradient (inside acidic) or a transmembrane difference in electrical potential (inside positive). Both the pH gradient delta pH and the membrane potential delta psi can drive monoamine uptake into chromaffin granule membrane vesicles (ghosts). The monoamine concentration gradient is proportional to the square of the [H+] gradient and to exp(F delta psi/RT). This implies that monoamine uptake occurs via a proton antiport or exchange diffusion mechanism with a stoichiometry of two protons per cationic amine.