Abstract
A comparative study of the noradrenaline storing vesicles in vas deferons from ox and rat was performed. Microsomal fractions were subjected to density gradient centrifugation. In rat, noradrenaline and dopamine β-hydroxylase were mainly present in the upper fractions of the gradient, which is consistent with the predominance of light (small dense-core) vesicles in this species. In ox, noradrenaline, dopamine and dopamine β-hydroxylase were found in the gradient in a bimodal distribution. This is consistent with the presence of about equal numbers of small and large dense-core vesicles in this species. On the other hand, chromogranin A, immunologically related proteins and enkephalin-like immunoreactivity were only present in the dense (large dense-core) vesicle population. In order to study the capability of light and dense vesicles to synthesize noradrenaline we “pulse-labelled” ox vasa deferentia with [ 3H]tyrosine. Already 3.5 min after the pulse both types of vesicles contained [ 3H]noradrenaline and [ 3H]dopamine. During longer “chase” periods the amount of [ 3H]dopamine gradually declined. We conclude that dense (large dense-core) vesicles contain chromogranin A, immunologically related proteins and enkephalin-like immunoreactivity whereas light (small dense-core) vesicles are devoid of these components. Both types of vesicles contain dopamine β-hydroxylase and can synthesize noradrenaline from dopamine under in vivo conditions.
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