The effect of salt regimens on the development of (Na +-K +)-dependent ATPase activity during the growth of salt glands of ducklings

Abstract

1. 1. A Mg 2+-activated, ouabain-sensitive (Na +-K +)-ATPase and a ouabain-insensitive Mg 2+-ATPase were characterized in salt gland homogenates of the domestic duck. 2. 2. 3 days after hatching, experimental birds were given 1% aqueous NaCl to drink for 12 h and fresh water for the remainder of each day. Control ducklings were maintained exclusively on fresh tap water. In homogenates of salt glands from experimental birds the specific activity of ATPase reached maximal levels in 9 days. (Na +-K +)-ATPase increased by a factor 4.1 and Mg 2+-ATPase increased by a factor of 1.8. There was no increase in ATPase activity in homogenates from control birds. 3. 3. Homogenates of glands from birds drinking only fresh water, after being maintained on the salt-water regimen for 22 days, exhibited a logarithmic decrease in (Na +-K +)-ATPase activity and in 9 days reached the level of activity recorded for control birds maintained only on fresh water. The Mg 2+-ATPase activity decreased rather slowly for the first 5 days on fresh water, and then dropped rapidly during the last 4 days of the experiment. 4. 4. The increase in ATPase levels in the salt glands of birds on the salt-water regimen is not cation-specific: both KCl and MgCl 2 regimens are capable of increasing this level, although neither is as effective as NaCl. 5. 5. Differential rates of increase and decrease of (Na +-K +)-ATPase and Mg 2+-ATPase activity resulting from various salt diets suggest that these activities may not be a consequence of bimodal functioning of the same enzyme.