Inhibition of sodium-plus-potassium-stimulated adenosine triphosphatase (Na+-K+-ATPase) by protein kinase C activators in the gills of Atlantic cod (Gadus morhua)

Abstract

Exogenous (phorbol ester) and endogenous (diacylglycerol) activators of protein kinase C (PKC) inhibited sodium efflux across the gills of Atlantic cod Gadus morhua and inhibited sodium-plus-potassium-stimulated adenosine triphosphatase (Na+-K+-ATPase) in isolated chloride cells. The branchial sodium efflux measured in a perfused whole-body preparation was inhibited by 47% on administration of 10−6 mol.L−1 phorbol 12, 13-dibutyrate (PDB). The branchial perfusion pressure was increased by 46% by 10−6 mol.L−1 PDB. In contrast the synthetic diacylglycerol, 1-oleoyl-2-acetyl gycerol (OAG) did not alter significantly perfusion pressure but did reduce sodium efflux by 13% at a concentration of 4 × 10−6 mol.L−1. The effects of these agents on Na+-K+-ATPase activity were determined in isolated chloride cells with a control activity of 30.9 ± 1.9 μmol Pi mg protein−1 hour−1. PDB and OAG both inhibited enzyme activity in a dose-dependent manner, with 10−5 mol.L−1 causing 45% and 26% inhibition, respectively. These results suggest that PKC is involved in regulating sodium efflux in the gills of cod by modulating Na+-K+ATPase activity.