UPTAKE OF MANGANESE BY CHROMAFFIN GRANULES IN VITRO

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Abstract
Abstract– The distribution of metal ions in the chromaffin granule is anomalous. Calcium ions are accumulated but magnesium ions excluded. We have used the manganese ion as a convenient divalent element for following metal ion uptake because it can usefully be employed as a substitute for magnesium.The kinetics of the manganese incorporation were followed by radio tracer technique and its transport was characterized as being non‐energy dependent and having a small thermal activation factor. The presence in the incubation medium of a membrane‐bound ATPase inhibitor (NEM) or addition of CN− or NaN3 did not affect the metal incorporation into chromaffin granules. Little endogenous magnesium exchanges for manganese when the latter is incorporated, but magnesium competitively prevented manganese uptake. The binding of manganese inside the vesicle was strong and it was not exchangeable with magnesium even in the presence of ATP.Manganese when incorporated binds to ATP and displaces catecholamines resulting in a decrease in the CA/ATP ratio.