Muscarinic responses of gastric parietal cells |
| |
Authors: | Jonathan M Wilkes Masayoshi Kajimura David R Scott Stephen J Hersey George Sachs |
| |
Institution: | (1) Center for Ulcer Research and Education, Department of Medicine, University of California at Los Angeles, 90073 Los Angeles, California;(2) Department of Physiology, Emory University, 30322 Atlanta, Georgia |
| |
Abstract: | Summary Isolated rabbit gastric glands were used to study the nature of the muscarinic cholinergic responses of parietal cells. Carbachol (CCh, 100 m) stimulation of acid secretion, as measured by the accumulation of aminopyrine, was inhibited by the M1 antagonist, pirenzepine, with an IC50 of 13 m; by the M2 antagonist, 11,2-(diethylamino)methyl-1 piperidinyl acetyl-5,11-dihydro-6H-pyrido 2,3-b 1,4 benzodiazepin-6-one (AF-DX 116), with an IC50 of 110 m; and by the M1/M3 antagonist, diphenylacetoxy-4-methylpiperidinemethiodide (4-DAMP), with an IC50 of 35nm. The three antagonists displayed equivalent IC50 values for the inhibition of carbachol-stimulated production of14CO2 from radiolabeled glucose, which is a measure of the turnover of the H,K-ATPase, the final step of acid secretion. Intracellular calcium levels were measured in gastric glands loaded with FURA 2. Carbachol was shown to both release calcium from an intracellular pool and to promote calcium entry across the plasma membrane. The calcium entry was inhibitable by 20 m La3+. The relative potency of the three muscarinic antagonists for inhibition of calcium entry was essentially the same as for inhibition of acid secretion or pump related glucose oxidation. Image analysis of the glands showed the effects of carbachol, and of the antagonists, on intracellular calcium were occurring largely in the parietal cell. The rise in cell calcium due to release of calcium from intracellular stores was inhibited by 4-DAMP with an IC50 of 1,7nm, suggesting that the release pathway was regulated by a low affinity M3 muscarinic receptor or state; Ca entry and acid secretion are regulated by a high affinity M3 muscarinic receptor or state, inhibited by higher 4-DAMP concentrations (>30nm), suggesting that it is the steady-state elevation of Ca that is related to parietal cell function rather than the Ca]
i
transient. Displacement of3H N-methyl scopolamine (NMS) binding to purified parietal cells by CCh showed the presence of two affinities for CCh, but only a single affinity for 4-DAMP and lower affinity for pirenzepine and AFDX 116, providing further evidence for the parietal cell location of the Ca]
i
response. Elevation of steady-state Ca]
i
levels with either ionomycin or arachidonic acid did not replicate M3 stimulation of acid secretion or glucose oxidation, hence elevation of Ca]
i
is necessary but not sufficient for acid secretion. |
| |
Keywords: | acid secretion carbachol gastric glands digital image analysis intracellular calcium muscarinic receptor subtype muscarinic binding parietal cell |
本文献已被 SpringerLink 等数据库收录! |
|