Acid secretion in α-toxin-permeabilized gastric glands

Abstract

Rabbit gastric glands were treated with α-toxin to test for permeabilization of basolateral membrane and retention of functional activity of parietal cells. Treatment with up to 400 U α-toxin/mL resulted in a dose-dependent increase in permeabilization, as judged by nuclear uptake of trypan blue (960 daltons), while causing relatively little loss of cytoplasmic macromolecules in the size range of lactate dehydrogenase (134 000 daltons). In the presence of cAMP and ATP, α-toxin-permeabilized resting gastric glands were stimulated to accumulate aminopyrine by ~10-fold over glands incubated without added nucleotides. Aminopyrine accumulation in stimulated permeabilized glands was inhibited by specific H+,K+-ATPase inhibitors, omeprazole and SCH-28080, and by the selective inhibitor of protein kinase A, H-89 (IC50 = 7.17 ± 2.05 μM; n = 4). Aminopyrine accumulation in the α-toxin-treated glands was dependent on both exogenous ATP and cAMP; however, when no exogenous ATP was present, cAMP-activated aminopyrine accumulation reached ~50% of maximum, and at levels of ATP > 0.05 mM, maximal aminopyrine accumulation occurred without exogenous cAMP. In the presence of ATP alone, aminopyrine accumulation in permeabilized glands achieved 61.1 ± 3.2% (n = 10; range, 50–70%) of the values measured on paired samples of intact glands stimulated with histamine plus isobutylmethylxanthine. These results demonstrate the functional responsiveness of α-toxin-permeabilized resting gastric glands. The participation of a protein kinase A dependent pathway during activation of permeabilized parietal cell is proposed.Key words: aminopyrine accumulation, H+,K+-ATPase, H-89, protein kinase A, oxidative phosphorylation, digitonin.