Insulin regulates ionic metabolism in a fresh water teleost, <i>Anabas testudineus </i>(Bloch)

Abstract

Short term effects of insulin on total brain and branchial Na⁺K⁺ATPase, Ca²⁺ATPase and Na⁺, K⁺ and Ca²⁺ ions were investigated in <i>A. testudineus. </i>The increase in brain Ca²⁺ ATPase after alloxan treatment may account for an increased amount of intracellular calcium required for biochemical events taking place inside the cells. Branchial Na⁺K⁺ATPase was

significantly stimulated while Ca²⁺ ATPase significantly inhibited after alloxan treatment. This suggests that alloxan exerts its inhibitory effect on the ATP-driven Ca²⁺ transport via; its action on the Ca²⁺ pump protein rather than the membrane permeability to Ca²⁺. The increased activity of brain Na⁺K⁺ ATPase at 3 and 24 hr by insulin to alloxan pretreated fish may account for the stimulated co-transport of glucose and its utilization for energy requirements and the excitatory action on neurons in the brain. The elevated brain Ca²⁺ ATPase may be due to the role of calcium as a second messenger in hormone action. At 24 hr, the activity of branchial Na⁺K⁺ ATPase and Ca²⁺ ATPase in alloxan pretreated specimens was significantly stimulated by insulin. This may be due to increased synthesis of these enzyme units. Administration of insulin (1U/fish) in normal fish significantly inhibited the activity of brain and branchial Na⁺K⁺ ATPase while brain Ca²⁺ATPase showed a

stimulatory effect at 3 and 24 hr compared to control. Inhibition of total branchial Ca²⁺ ATPase activity by insulin may be due to increased Ca²⁺ concentration. Higher plasma glucose level in alloxan treated groups confirms the diabetic effect of alloxan. Insulin reverses this effect. The possible mechanism by which insulin controls Na⁺K⁺ ATPase activity appears to be tissue specific. The results seem to be the first report on the effect of insulin on ATPase activity in a teleost. These data are consistent with the hypothesis that insulin performs a role in hydro mineral regulation in freshwater teleosts.