Molecular Pharmacology, Vol 7, 52-65, Copyright © 1971 by the American Society for Pharmacology and Experimental Therapeutics

Phosphorylation of Membrane Components of Adrenal Chromaffin Granules by Adenosine Triphosphate

¹ Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada

Adenosine triphosphate acts on chromaffin granules of the adrenal medulla to produce structural changes and release of catecholamines, endogenous ATP, and soluble protein. When ATP exerts this action on chromaffin granules, it is hydrolyzed by the Mg⁺⁺-dependent ATPase present in the granule membrane, and part of the P_i liberated from ATP under the action of the granule ATPase is transferred to the chromaffin granule membrane. This transphosphorylation from ATP is Mg⁺⁺-dependent and temperature-sensitive; substitution of Mn⁺⁺ for equimolar concentrations of Mg⁺⁺ potentiates the effect, but Ca⁺⁺ has no significant effect on the transphosphorylation from ATP. This phosphorylation is also blocked by inhibitors of the Mg⁺⁺-dependent mechanism of catecholamine release, such as N-ethylmaleimide and gramicidin. Ouabain and atractyloside, which were ineffective in blocking ATP-evoked catecholamine release, did not inhibit the membrane phosphorylation.

The membrane phosphorylation was due to an active transfer of phosphate from ATP to the chromaffin granule membranes, rather than to binding of the nucleotide to the chromaffin granule structures or to the secondary incorporation of the P_i freed into the incubation medium.

The similarities among ATPase activity, ATP-evoked catecholamine release, and phosphorylation of the membrane of chromaffin granules by ATP are discussed. This membrane phosphorylation is, to our knowledge, the first demonstration of a phenomenon of this nature in a granule that stores or releases hormones.

Note:
ACKNOWLEDGMENTS We thank Dr. R. Blostein, Department of Experimental Medicine, McGill University, for advice in the synthesis of [-³²P]ATP, and Mr. S. Iu for technical assistance. We are also grateful to Dr. B. Collier for reading the manuscript.