Osmotic lysis of bovine chromaffin granules in isotonic solutions of salts of weak organic acids. Release of catecholamines, ATP, dopamine beta-hydroxylase, and enkephalin-like material.

Chromaffin granules in isotonic solutions of K+ CH3COO- (acetate), K+ CH3CHOHCOO- (lactate), and K+2-OOCCH2CH2COO- (succinate) are stable at pH 7 but release 40 to 80% of their soluble contents of catecholamines, ATP, and dopamine beta-hydroxylase when the medium pH is less than 6. Enkephalin-like material which has recently been shown to co-sediment with chromaffin granules in sucrose density gradients is also released at low pH. The release of ATP and enkephalin-like material is proportional to the release of catecholamine. The release of soluble constituents of chromaffin granules is inhibited by increasing the osmolality of the solution with sucrose. Granules in isotonic solutions of salts of strong acids such as K+CH3SO4- (methylsulfate), K+ CH2OHCH2SO3- (isethionate), and K2SO4 are stable between pH7.0 and 5.4. The granules behave as predicted for organelles with an acid interior and the data provide further evidence that the intragranular pH is acidic. In addition, the results strongly suggest that enkephalin-like material is stored together with catecholamine and ATP in an acid compartment.