Action of adenosine on energetics, protein synthesis and K(+) homeostasis in teleost hepatocytes.

Abstract

In a comparative study, we analysed the effects of adenosine on the energetics, protein synthesis and K(+ )homeostasis of hepatocytes from the anoxia-tolerant goldfish Carassius auratus and the anoxia-intolerant trout Oncorhynchus mykiss. The rate of oxygen consumption did not respond immediately to the addition of adenosine to the cells from either species, but showed a significant decrease in trout hepatocytes after 30 min. The anaerobic rate of lactate formation was not significantly affected by adenosine in goldfish hepatocytes, but was increased in trout cells. We also studied the effects of adenosine on the two most prominent ATP consumers in these cells, protein synthesis and Na(+)/K(+)-ATPase activity. Under aerobic conditions, adenosine inhibited protein synthesis of hepatocytes from goldfish by 51% and of hepatocytes from trout by 32%. During anoxia, the rate of protein synthesis decreased by approximately 50% in goldfish hepatocytes and by 90% in trout hepatocytes, and this decrease was not altered by the presence of adenosine. Adenosine inhibited normoxic Na(+)/K(+)-ATPase activity and K(+ )efflux by 20-35% in the cells of both species. An investigation into the mechanism underlying the inhibition of protein synthesis by adenosine indicated that, in the goldfish cells, adenosine acts via a membrane receptor-mediated pathway, i.e. the effect of adenosine was abolished by applying the A1 receptor antagonist 8-phenyltheophylline. In the trout, however, the uptake of adenosine into hepatocytes seems to be required for an effect on protein synthesis. [Ca(2+)](i) does not seem to be involved in the inhibition of protein synthesis by adenosine.