Effects of β-ecdysone and juvenile hormone on the Na +/K +-dependent ATPase in imaginal disks of Drosophila melanogaster

Abstract

The evagination of imaginal disks of Drosophila melanogaster is induced in vitro by β-ecdysone and inhibited by juvenile hormone. The possibility that these hormones act by changing intracellular Na + and K + levels was investigated by studying their effects on the sodium-potassium dependent adenosinetriphosphatase (NaK ATPase), an enzyme with a major rôle in regulating Na + and K + levels in cells. We find that β-ecdysone has no effect on this enzyme and can induce evagination even when intracellular Na + concentrations are increased 2 to 3 fold by ouabain. Juvenile hormone stimulates the enzyme, but still acts to inhibit evagination when NaK ATPase activity is inhibited by ouabain. We conclude that the actions of β-ecdysone and juvenile hormone on imaginal disk evagination do not directly involve the NaK ATPase or require specific changes in Na + and K + concentrations.