P-31 NUCLEAR MAGNETIC-RESONANCE STUDIES OF PIG ADRENAL-GLANDS

31P NMR was used to study the secretion of ATP from the medulla of perfused pig adrenal glands. The resonances of the nucleotide pools in the chromaffin granules and cytoplasm are clearly resolved and, therefore, the intragranular and cytoplasmic processes involving ATP can be monitored simultaneously in the gland during secretion. Secretion of nucleotide during a 3 h continuous stimulation by infusion of acetylcholine chloride was monitored by the decrease in intensity of the intragranular ATP resonances. Up to 40% of the total intragranular nucleotide was released under these conditions. The rate of secretion decreased with duration of stimulation. No significant changes in the steady-state levels of cytoplasmic ATP or in O consumption were observed. The intragranular pH in ischemic glands was 5.52 + 0.15, while in glands which had been perfused until their cytoplasmic nucleotide levels had recovered, the intragranular pH was 5.76 .+-. 0.16. The 1st estimate of the internal pH of the chromaffin granules in intact perfused adrenal glands is provided and no net acidification occurs in the presence of cytoplasmic ATP. The isolated chromaffin granule possesses a proton-pumping ATPase which, in the presence of a permeant counter-ion, such as Cl, acidifies the granule interior. In the intact cell, the cytoplasmic concentration of permeant counter-ions is too low to allow electrically neutral proton accumulation in the granules.