PLATELET-ACTIVATING-FACTOR STIMULATES GASTRIC-ACID SECRETION IN ISOLATED RABBIT GASTRIC GLANDS

We examined the effect of platelet-activating factor (PAF) on gastric acid secretion by isolated rabbit gastric glands as determined by [C-14]aminopyrine ([C-14]AP) uptake. PAF, histamine, and carbachol time- and concentration-dependently stimulated [C-14]AP uptake, with estimated half-maximal effective concentrations of 60 pM, 0.25 mu M, and 0.1 mu M, respectively. PAF-induced [C-14]AP uptake was inhibited by the specific PAF antagonists BN-50727 and SR-27417 and by the proton pump inhibitors omeprazole and lansoprazole. However, the H-2-receptor antagonist famotidine had no effect. Buffering extracellular Ca2+ by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid resulted in a shift to the right of the time-course effect of PAF without altering the maximal response, whereas buffering intracellular Ca2+ by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N' -tetraacetic acid 2-acetoxymethyl ester, as well as blocking Ca2+ channels by verapamil, inhibited PAF-induced [C-14]AP uptake. Intracellular Ca2+ concentration in isolated rabbit gastric glands, as measured by fura 2-acetoxymethyl ester, concentration-dependently increased in response to PAF, to a maximum of 1.5-fold for 0.1 mu M. These results suggest that PAF stimulates gastric acid secretion via specific receptors activating intracellular Ca2+ mobilization, which could be located on the parietal cells.