FIGURE 9.

Isoform content and Na,K-ATPase activity of α2/α3 versus α1 isoforms in rat heart sarcolemma membranes. a, immunoblots using isoform-specific antibodies of α1, α2, and α3 to determine isoform content of rat heart sarcolemma membranes. Calibration of the signals used was 0.05–2 μg of purified human α1β1, α2β1, and α3β1 complexes. The calculated amounts of the isoforms are given in micrograms. b, ATPase activity of rat heart sarcolemma membranes measured in the standard reaction medium containing 0, 30 μm, or 5 mm ouabain. Na,K-ATPase attributable to α2 + α3 and α1 were calculated from control activity − activity at 30 μm and activity at 30 μm − activity at 5 mm ouabain, respectively. The data represent one of several similar experiments.