Effect of cadmium chloride on rat brain synaptosomal ATPases

Cadmium has been shown to alter membrane-bound ATPases both in vitro and in rats treated with the metal. However, cadmium effects on the substrate and ionic activation kinetics of Na+-K+ ATPase activity were determined by a coupled enzymatic method. A concentration-response curve was determined using 5-30 microM cadmium chloride in the reaction medium. The data showed a 50% inhibition at 15 microM cadmium chloride. Cadmium effects on ATP, Na+ and K+ activation of Na+-K+ ATPase were determined by varying the concentration of these substrates at 15 microM cadmium chloride. The double-reciprocal plots showed that cadmium inhibition of Na+-K+ was competitive with ATP and Na+ in that the Km values were increased but not the Vmax values. In contrast, cadmium inhibition was noncompetitive with K+ activation where both Km and Vmax values were decreased. The present data suggest that cadmium may be competing with ATP and Na+ sites on Na+-K+ ATPase in rat brain synaptosomes.