Fig. 4. Effect of in vitro incubations to stimulate the activities of endogenous (A) protein kinases and (B) protein phosphatases on Na⁺/K⁺-ATPase activity in foot muscle extracts from active and 10-day estivated O. lactea. Incubation time was 4 h prior to assay under V_max conditions at 22°C. Values are means ± s.e.m., N=4 independent determinations. ^*Significantly different from the corresponding control incubation; Student's t-test, P<0.01; P<0.05. For details of incubation conditions, see Materials and methods.