Table 1.

Resting membrane potentials at selected [k⁺]₀ in isolated ventricular myocytes

	0.5 mm	2.5 mm	5 mm	7 mm	10 mm	15 mm
Measured	−27.6 ± 1.63	−102.2 ± 1.89	−86.5 ± 1.03	−80.1 ± 1.25	−73.6 ± 1.02	−66.4 ± 1.03
Calculated	−143.2	−102.3	−84.7	−76.1	−67.0	−56.7

For all groups, n = 7. Membrance patentials (mV) were determinded at 22°C while Ca²⁺ -imaging experiments were conducted at 35°C. The resting membrance potentials at 35°C, calculated using the Nernst equation, for the selected [K⁺]₀ were: 0.5 mm, –149.5 mV; 2.5 mm, –168.8 mV; 5 mm, –88.4 mV; 7mM, –79.5 mV; 10 mm, –70.0 mV; 15 mm, –59.3 mV. The deviation of the measured resting membrance potential from the calculated value seen in 0.5 mm [K⁺]₀ was expected due to the K⁺ -sensing function of the invwardly rectifying background K⁺ current, I_K1 (Pandit et al. 2001). Based on these findings, in the Ca²⁺ -imaging experiments, diastolic membrance potential was altered by changing [K⁺]₀.