Figure 2.

Saponin unmasked db-cAMP-stimulated Na,K-ATPase hydrolytic activity in rat CCD. Microdissected CCDs were preincubated in the absence or presence of 10⁻³ M db-cAMP for 30 min at 37°C. The hydrolytic activity of Na,K-ATPase was measured after permeabilization of cell membranes by using the freeze/thawing procedure or by incubating CCDs with 0.5 mg · ml⁻¹ saponin for 10 min at room temperature. Values (means ± SE from 5 independent experiments) are expressed as percentage of controls (486 ± 50 pmol ATP · mm⁻¹ · h⁻¹). ∗, p < 0.05 versus control values.