Similarities and differences in oxynticopeptic cell ultrastructure of one marine teleost, Gadus morhua and one freshwater teleost, Oncorhynchus mykiss, during basal and histamine-stimulated phases of acid secretion

Oxynticopeptic cells (OC) from rainbow trout, Oncorhynchus mykiss, and Atlantic cod, Gadus morhua, were studied during basal acid secretion and during stimulation with histamine. An in vitro method for measuring acid secretion from isolated stomac a was used. The OC ultrastructure was studied using electron microscopy. During basal acid secretion, the OC had short apical microvilli, an extensive tubulovesicular network, large electron-dense vesicles and many mitochondria. Stimulation of acid s tion with histamine and ultrastructural changes in the OC occurred simultaneously. The acid stimulation promoted large increases in the length of microvilli, a decrease in the size of the tubulovesicular network and an increase in the diameter of the ndular lumen in cod. Large vacuoles were found to characterize the histamine-stimulated OC. These were located close to the apical membrane and sometimes opened into the lumen. During stimulation, electron-dense vesicles were often observed close to apical membrane and the large vacuoles. Sometimes these vesicles were observed inside the glandular lumen and/or the large vacuoles. It is concluded that the ultrastructure of the OC in the saltwater cod and the freshwater trout show similar characte ics as OC in other animal groups both during basal and high rates of acid secretion. In addition, vacuoles were found in both species OC during basal rates of acid secretion and they significantly increased in size during high rates of acid secretion propose that the OC vacuole have a part in the osmoregulation, since the increase was tenfold in cod but less then one-fold in trout, this difference was statistically significant.