ROLES OF ADRENOCEPTORS IN ISOLATED CANINE PARIETAL-CELLS

Functional roles of adrenoceptors in parietal cells were pharmacologically investigated using isolated canine parietal cells. In the crude membranes obtained from preparations highly purified in parietal cells (>95% of purity), the specific binding of [H-3]dihydroalprenolol (DHA) was observed with a Kd value of 2.9 nM and B-max of 234 fmol/mg protein, while the specific binding of [H-3]prazosin and [H-3]rauwolscine were not attained. Propranolol concentration-dependently reduced the specific binding of [H-3]dihydroalprenolol with a K-i value of 2.6 nM. Isoproterenol concentration-dependently stimulated [C-14]aminopyrine accumulation in preparations enriched in parietal cells (about 70% purity) with the maximum at 10 nM. Isoproterenol increased the content of cyclic AMP in preparations enriched in parietal cells (70%) with the maximum at 100nM. The isoproterenol-induced stimulatory effect of [C-14]aminopyrine accumulation in preparations enriched in parietal cells (70%) was completely abolished by 1 mu M propranolol but not by 1 uM phentolamine. In the presence of 1 mu M propranolol, 100 mu M noradrenaline did not affect carbachol- and histamine-induced [C-14]aminopyrine accumulation in preparations enriched in parietal cells (70%). The present study suggests that stimulation of beta-adrenoceptors located on canine parietal cells evokes acid production in a cyclic-AMP-dependent manner. Furthermore, a possibility arises that canine parietal cells are not the site of action of alpha-adrenoceptors in mediating inhibition of gastric acid secretion.