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 [3H]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 [3H]prazosin and [3H]rauwolscine were not attained. Propranolol concentration-dependently reduced the specific binding of [3H]dihydroalprenolol with a K_i value of 2.6 nM. Isoproterenol concentration-dependently stimulated [14C]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 100 nM. The isoproterenol-induced stimulatory effect of [14C]aminopyrine accumulation in preparations enriched in parietal cells (70%) was completely abolished by 1 μM propranolol but not by 1 μM phentolamine. In the presence of 1 μM propranolol, 100 μM noradrenaline did not affect carbachol- and histamine-induced [14C]aminopyrine accumulation in preparations enriched in parietal cells (70%). The present study suggests that stimulation of β-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 α-adrenoceptors in mediating inhibition of gastric acid secretion.