FIGURE 3.

Effect of forskolin on Na⁺-K⁺ pump current in myocytes. Panel A shows the timing of changes in the composition of superfusates. The arrow on the left side of the panel indicates establishment of the whole-cell configuration and, hence, perfusion of the intracellular compartment with pipette solution. The switch from a Ca²⁺-containing, forskolin-free solution in the tissue bath to a nominally Ca²⁺-free solution containing Ba²⁺, Cd²⁺, and forskolin and the switch to a solution also containing ouabain (the arrow on the right side of the panel) are shown. Panel B shows examples of holding currents. Large changes in the currents that occur the first 1–2 min after the switch to Na⁺- and Ca²⁺-free Ba²⁺- and Cd²⁺-containing superfusate before currents stabilize are not shown. Stable holding currents before exposure of myocytes to ouabain are important for the measurement of I_p. Stability of the currents as well as the ouabain-induced shift in them was identified from the read-out of an electronic cursor. C_m indicates membrane capacitance in picofarads (pF). Panel C shows the mean I_p normalized for membrane capacitance. The pipette solution contained l-arginine where indicated. The numbers of myocytes in each group are indicated in parentheses. The asterisk indicates a significant difference between the means of I_p.