INFLUENCE OF COLD EXPOSURE ON THE ACTIVITIES OF SOLUBLE AND MEMBRANE-BOUND DOPAMINE β-HYDROXYLASE IN RAT HEART VESICLES

Abstract— A fraction containing noradrenaline storage vesicles of the sympathetic nerve terminals in the rat heart was obtained by differential centrifugation. In this preparation, 17% of the dopamine β-hydroxylase was present in a soluble form. Cold exposure (3°C) for periods from 5 to 30 min led to an increase in the activity of soluble dopamine β-hydroxylase by about 50%, while the activity of membrane-bound dopamine β-hydroxylase was simultaneously decreased by approx 30%. The nor-adrenaline content of the vesicles rose concomitantly with the increase in the activity of soluble dopamine β-hydroxylase. This rise in noradrenaline content was caused by an enhanced synthesis and not by an alteration in the subcellular distribution. The results are discussed with respect to the fate of dopamine β-hydroxylase during enhanced sympathetic nerve activity.