Inhibition of duodenal enterocyte Mg2+-ATPase by arachidonic acid is not mediated by an effect on protein kinase C

Active absorption processes in the duodenal enterocyte are driven by variou s ATPases. It is known that the activity of Na+,K+-ATPase, Ca2+- ATPase and Mg2+-ATPase can be modulated by polyunsaturated fatty acids of the n-6 ser ies, for example by linoleic and gamma-linolenic acids. These effects may b e achieved by protein phosphorylation via protein kinase C. The present stu dy was undertaken to determine the effect of arachidonic acid on Mg2+-ATPas e (measured colorimetrically) activity in basolateral membranes prepared fr om rat duodenum. It shows, for the first time, significant dose-dependent i nhibition of Mg2+- ATPase (26-62%) by arachidonic acid (10-50 mu g/ml) whic h already takes place after one minute of exposure, indicating involvement of a rapid signal transduction mechanism. Addition of the protein kinase C inhibitors bisimidolylmaleimide (2.5 mu M) and calphostin (0.5 mu M) did no t influence the action of arachidonic acid on Mg2+- ATPase; protein kinase C involvement in this process is thus not indicated. (C) 2000 Harcourt Publ ishers Ltd.