Hemodynamics and potentials in isolated flounder gills: effects of catecholamines

Branchial hemodynamics and transepithelial potentials were investigated in an isolated perfused gill preparation from the flounder (Platichthys flesus L.). An analysis of the pressure-flow profiles suggests that the gill is compliant but that the physical relationships of pressure and flow are complex. Epinephrine has a bimodal effect with an initial vasoconstriction followed by a vasodilation, the latter response being much smaller than that usually seen in teleosts. Pharmacological analysis shows 1) an alpha-mediated vasoconstriction of the arterial and venous pathway, associated with a redistribution of flow away from the venous pathway, and 2) a small beta-mediated vasodilation of the arterial pathway only. An electrical potential (inside positive) was measured across the isolated gill, bathed and perfused with an identical saline. This potential was recorded, despite the venous system being open to the external bath, and was independent of both arterial and venous flows. Epinephrine caused a significant decline in this potential, which could be resolved into a large inhibitory alpha-mediated response and a small beta-mediated stimulation.