Abstract

A light-scattering technique has been employed to investigate changes in isolated bovine adrenal medullary chromaffin granules associated with release of catecholamines. The optical density (OD) at 540 mµ of chromaffin granule suspensions was proportional to the concentration of granules. ATP (0.5 mM) produced a fall in OD in the presence of 0.5 mM Mg or Mn, but not in that of Ca, Ba, or Sr. ADP produced a small fall in OD which was delayed in onset, whereas AMP was ineffective. The effect of ATP was inhibited by NEM and AMP, and was abolished by 0.3 M sucrose. In all the above conditions there was a correlation between fall in OD and release of catecholamines. The results suggest that ATP produces some change in the structure of chromaffin granules leading to the release of catecholamines and that granule ATPase may be involved in the change.