Fig. 6. Effect of calcium concentration on the stimulation by endogenous protein kinases of Na⁺/K⁺-ATPase activity in foot muscle extracts from active snails. In vitro incubations stimulated PKA, PKC or PKG and the resulting change in Na⁺/K⁺-ATPase activity is expressed as a percentage of the activity in control incubations where protein kinases were not stimulated. Other information as in Fig. 4. ^*Significantly different from the corresponding incubation with zero calcium concentration; Student's t-test, P<0.01.