Selective loss of IK,slow in SWAP and Kv2.1−/− ventricular myocytes reduces palmitate-sensitive K+ currents. (A) Outward K+ currents, evoked in response to 4.5 s voltage steps from a holding potential of −70 mV to +40 mV at 15 s intervals, were recorded from WT, SWAP and Kv2.1−/− LVA myocytes under control conditions (a) and following superfusion of palmitate:BSA (30 µM:60 µM)(b). The amplitudes of the outward K+ currents in LVA myocytes isolated from WT, SWAP and Kv2.1−/− mice were increased on application of palmitate:BSA The palmitate-sensitive currents (a–b) were obtained by off-line digital subtraction of the currents recorded in palmitate:BSA (b) from the control (a) records in the same cell. (B) Comparison of the waveforms of the palmitate-sensitive K+ currents in WT (black), SWAP (red) and Kv2.1−/− (blue) LVA myocytes. The mean ± SEM densities of the palmitate-sensitive outward K+ currents (C) and the palmitate dependent decrease in fractional shortening (D) are significantly (**P<0.01) lower in SWAP and in Kv2.1−/−, than in WT, LVA myocytes.