The effects of the adrenoreceptor agonists phenylephrine and isoproterenol on the intracellular ion concentrations of branchial epithelial cells of brown trout (Salmo trutta L.)

Abstract

Brown trout were fitted with indwelling, intraperitoneal catheters and injected with 4–6 μmol · kg^-1 of the α-receptor agonist phenylephrine or the β-receptor agonist isoproterenol. The intracellular concentrations of sodium, chlorine, potassium and phosphorus in the pavement epithelial cells and the mitochondria-rich cells of the branchial epithelium were measured by X-ray microanalysis 1 h after the injection of the adrenoreceptor agonists. Injection with phenylephrine resulted in a significant increase in intracellular chlorine and potassium in mitochondria-rich cells and a significant but relatively smaller increase in chlorine in pavement epithelial cells. Injection with isoproterenol resulted in a significant increase in sodium and chlorine concentration in pavement epithelial cells and a significant decrease in potassium concentration. The only significant effect of isoproterenol injection on mitochondria-rich cells was a decrease in intracellular chlorine concentration. The results suggest that these adrenoreceptor agonists have a direct effect on the influx of Na⁺ and Cl^- across the branchial epithelium. These effects may be a mechanism for acid-base regulation during the severe stress conditions that elicit catecholamine release in vivo. These results corroborate previous studies using X-ray microanalysis which suggested that pavement epithelial cells are the sites of Na⁺ uptake in freshwater fish whilst Cl^- uptake occurs via mitochondria-rich cells.