Figure 4. Increased EE and mechanical function of Kir6.2-KO isolated hearts.

(A) Rate of oxygen consumption, measured in isolated perfused hearts revealed a significantly elevated energy demand in Kir6.2-KO versus WT (n=5 for each group).

(B) Pacing rates above 130 ms (460 beats/min) induced significant shortening of APD₉₀ in WT (n=8) that was sensitive to the sulfonylurea glyburide (10 µM, n=4) but not in hearts from Kir6.2-KO (n=5). Solid lines were constructed as results of quadratic polynomial fitting of experimental data relative to APD₉₀ at 150 ms pacing interval.

(C)Integrated left ventricular pressure was defined for 3–4 s long periods and divided by number of cardiac cycles in unpaced Kir6.2-KO and WT hearts (n=7 for each group).

(D and E) Overexpression of sarcolemmal Na⁺/K⁺ pumps in Kir6.2-KO compared to WT (n=3 for each group) revealed by Western blots.

(F) Histograms summarizing heart rates during 24-h long monitoring using telemetry in WT (n=11, top) and Kir6.2-KO (n=10, bottom). Dotted lines represent the fit of distributions with the sum of two Gaussian functions; solid lines indicate individual functions. Arrow indicates right shift of the lower mean heart rate in Kir6.2-KO relative to the corresponding value in WT.

Data are mean±SEM;*, p<0.05.