Presence of 5-hydroxytryptamine (serotonin) transport coupled with vacuolar-type H(+)-ATPase in neurosecretory granules from bovine posterior pituitary.

Abstract

Electrogenic H(+)-ATPase was found in neurosecretory granules from bovine posterior pituitary. This enzyme was sensitive to bafilomycin, a specific inhibitor of vacuolar H(+)-ATPase, and was inactivated completely by cold treatment in the presence of MgATP and NaNO3. Immunoblot analysis showed the presence of immunologically identical polypeptides (72, 57, and 34 kDa) in the ATPases of the neurosecretory granules and chromaffin granules. The granules showed MgATP-dependent activity for 5-hydroxytryptamine (serotonin) uptake. This uptake was temperature-dependent and showed saturation kinetics (apparent Km for 5-hydroxytryptamine, 2 microM) and counter-flow. Reserpine and tetrabenazine at 1 microM inhibited the uptake, whereas imipramine at 2 microM had no effect. Dopamine, epinephrine and norepinephrine were also inhibitory. The uptake was abolished by various treatments that dissipated the electrochemical H+ gradient or inhibited the H(+)-ATPase. These results indicate that a vacuolar type H(+)-ATPase in the neurosecretory granules forms an electrochemical H+ gradient that drives 5-hydroxytryptamine uptake by a specific transport system. A similar granular fraction from the anterior pituitary had no ATP-dependent activity for 5-hydroxytryptamine uptake.