Cell dialysis with the pipette solution during whole-cell voltage clamping may influence regulation of the cardiac Na⁺-K⁺ pump by direct or indirect phosphorylation. We have used the perforated-patch technique to limit cell dialysis and maintain conditions as near physiological as possible. Guinea-pigs were killed by cervical dislocation (in accordance with UK legislation), hearts excised and ventricular myocytes isolated using a standard enzymatic isolation procedure. Cells were plated onto the stage of an inverted microscope and electrodes (1-2 M¢) were used to record whole-cell currents using the perforated-patch technique. Pipette filling solutions contained 225 µg ml^-1 amphotericin B and were formulated along with the extracellular solutions to allow isolation of the Na⁺-K⁺ pump current. Whole-cell current was measured and the components of the Na⁺-K⁺ pump current (I_α1 and I_α2) were defined by their differing ouabain (DHO) sensitivities. I_α2 was represented by the 5 µM DHO-sensitive current, and the current additionally sensitive to 250 µM DHO represented I_α1. Both I_α1 and I_α2 were measured before, during and after the application of forskolin (1 µM), at 0 mV. DIDS (1 mM) and glibenclamide (200 µM) and also the use of symmetrical [Cl^–] of 17.5 mM in pipette and extracellular solutions limited forskolin-activated Cl^– conductance. Treatment with 1 µM forskolin for 4 min at 35 °C caused a significant (P < 0.05, paired t test, n = 6) increase in I_α1 of 36 ± 15 % (mean ± S.E.M.), but no change in I_α2. This potentiating effect of forskolin on I_α1 was blocked by the presence of 50 µM H-89 (PKA-selective inhibitor) throughout the protocol (n = 5). In cells untreated with forskolin, treatment with 50 µM H-89 for 4 min did not cause a significant change in I_α1 or I_α2 (P > 0.05, paired t test, n = 6). In separate experiments, forskolin (1 µM) raised cAMP from 15.0 ± 1.6 pmol (mg protein)^-1 to 27.0 ± 3.3 pmol mg^-1 after treatment for 4 min at 35 °C (P < 0.01, n = 6). Isoelectric focusing gels of the α₁-subunit demonstrated six charge states, which were unaltered by forskolin. Western blots using an antibody specific for the α₁-subunit PKA phosphorylation consensus site also showed no change in the phosphorylation status of the subunit following forskolin treatment. This work indicates a PKA-dependent α₁-specific activation of the Na⁺-K⁺ pump following elevation of cAMP. This may involve the phosphorylation of auxiliary proteins rather than a direct phosphorylation of the α₁-subunit itself.