| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2001: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 2000: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
The electrophysiological properties of the transient outward current were investigated in voltageclamped single cells from the rabbit sino-atrial node. The current-voltage relationship exhibited a characteristic outward rectification with an activation threshold of -30 mV. External 4-aminopyridine inhibited this current in a dose-dependent manner (IC50 = 0.28 mM, Hill coefficient = 1.38). The steady-state inactivation exhibited a half-maximum voltage of -35 mV and a slope factor of -8.4 mV. The current density of the transient outward current was 6.3 ± 0.5 pA/pF in sino-atrial node cells and 12.3 ± 1.2 pA/pF in atrial cells. The inactivation time constant was faster in sino-atrial node cells (time constants, 4.2 ± 0.5 ms and 26.0 ± 0.6 ms, respectively, for the fast and slow components) than in atrial cells (9.7 ± 1.2 ms and 44.8 ± 3.2 ms, respectively). Recovery from inactivation was much faster in sino-atrial node cells (time constant, 44.7 ± 9.0 ms) than in atrial cells (time constants, 1.39 ± 0.32 s and 6.70 ± 0.1 s, respectively, for the fast and slow components). These results suggest that the kinetic properties, as well as the current density, of the transient outward current differs between sino-atrial node and atrial cells. Taking the current density of Ito at +10 mV as 2.5 ± 0.3 pA/pF gives a total Ito of approximately 100 pA at the. peak of the action potential in rabbit sino-atrial node cells. Thus, Ito may contribute significantly to the repolarization phase in mammalian sino-atrial node cells.
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