NUCLEOTIDE-METABOLISM BY GASTRIC GLANDS AND H-K+-ATPASE-ENRICHED MEMBRANES()

alpha-Toxin-permeabilized gastric glands represent a functional model in which acid secretion can be elicited by either adenosine 3',5'-cycl ic monophosphate (cAMP) or ATP, with proven morphological and function al transition between resting and secretory states [X. Yao, S. M. Kara m, M. Ramilo, Q. Rong, A. Thibodeau, and J. G. Forte. Am. J. Physiol. 271 (Cell Physiol. 40): C61-C73, 1996.] In this study we use alpha-tox in-permeabilized rabbit gastric glands to study energy metabolism and the interplay between nucleotides to support acid secretion, as indica ted by the accumulation of aminopyrine (AP). When permeabilized glands were treated with a phosphodiesterase inhibitor, the secretory respon se to cAMP was inhibited, whereas the secretory response to ATP was po tentiated. This implied that 1) ATP provided support not only as an en ergy source but also as substrate for adenylate cyclase, 2) activation of acid secretion by cAMP needed ATP, and 3) ATP and cAMP exchanged r apidly inside parietal cells. To address these issues, we tested the a ction of adenine nucleotides in the presence and absence of oxidizable substrates. All adenine nucleotides, including AMP, ADP, ATP, and cAM P, could individually enhance the glandular AP accumulation in the pre sence of substrates, whereas only a high concentration of ATP (5 mM) w as able to support secretory activity in substrate-free buffer. Moreov er, ATP could maintain 75-80% of maximal secretory activity in phospha te-free buffer; cAMP alone could not support secretion in phosphate-fr ee buffer. In glands and in H+-K+-adenosinetriphosphatase-rich gastric microsomes, we showed the operation of adenylate kinase, creatine kin ase, and ATP/ADP exchange activities. These enzymes, together with end ogenous adenylate cyclase and phosphodiesterase, provide the recycling of nucleotides essential for the viability of alpha-toxin-permeabiliz ed gastric glands and imply the importance of nucleotide recycling for energy metabolism in intact parietal cells.