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Aim: The aim of the present study was to investigate the effect of the antibody against alpha-2 repeat on Na+-Ca2+ exchanger (NCX) current (I(Na/Ca)). To evaluate the functional specificity of this antibody, its effects on L-type Ca2+ current (I(Ca,L)), voltage-gated Na+ current (I(Na)) and delayed rectifier K+ current (I(K)) were also observed., Methods: The whole-cell patch-clamp technique was used in this study., Results: The antibody against alpha-2 repeat augmented both the outward and inward Na+-Ca2+ exchanger current concentration-dependently, with EC(50) values of 27.9 nmol/L and 24.7 nmol/L, respectively. Meanwhile, the antibody could also increase I(Ca,L) in a concentration-dependent manner with the EC(50) of 33.6 nmol/L. Effects of the antibody on I(Na) and I(K) were not observed in the present study., Conclusion: The present results suggest that antibody against alpha-2 repeat is a stimulating antibody to NCX and could also increase I(Ca,L) in a concentration-dependent manner, but did not have an obvious effect on I(Na) and I(K).

Calcium sensitizers exert positive inotropic effects without increasing intracellular Ca(2+). Thus, they avoid the undesired effects of Ca(2+) overload such as arrhythmias and cell injury, but most of them may impair myocyte relaxation. However, MCI-154, also a calcium sensitizer, has no impairment to cardiomyocyte relaxation. To clarify the underlying mechanisms, we examined the effects of MCI-154 on Ca(2+) transient and cell contraction using ion imaging system, and its influence on L-type Ca(2+) current and Na(+)/ Ca(2+) exchange current with patch clamp technique in rat ventricular myocytes as well. The results showed that: (1) MCI-154 (1-100 micromol/L) had no effect on L-type Ca(2+) current; (2) MCI-154 concentration-dependently increased cell shortening from 5.00+/-1.6 microm of control to 6.2+/-1.6 microm at 1 micromol/L, 8.7+/-1.6 microm at 10 micromol/L and 14.0+/-1.4 microm at 100 micromol/L, respectively, with a slight increase in Ca(2+) transient amplitude and an abbreviation of Ca(2+) transient restore kinetics assessed by time to 50% restore (TR(50)) and time to 90% restore (TR(90)); (3) MCI-154 dose-dependently increased the electrogenic Na(+)/ Ca(2+) exchange current both in the inward and the outward directions in rat ventricular myocytes. These results indicate that MCI-154 exerted a positive inotropic action without impairing myocyte relaxation. The stimulation of inward Na(+)/ Ca(2+) exchange current may accelerate the Ca(2+) efflux, leading to abbreviations of TR(50) and TR(90) in rat myocytes. The findings suggest that the improvement by MCI-154 of myocyte relaxation is attributed to the forward mode of Na(+)/ Ca(2+) exchange.

Aim: To study the effects of N-[4-[[1-[2-(6-methyl-2-pyridinyl)ethyl]-4-piperidinyl]carbonyl]phenyl]methanesulfonamide dihydrochloride dihydrate (E-4031), a specific Ik blocker, on Ca2+ transient and cell contraction of normal and hypertrophied rat ventricular myocytes., Methods: Electrically triggered Ca2+ transient and cell shortening were measured simultaneously using the Ion Imaging System with charge coupled digital (CCD) camera., Results: E-4031 (10 micromol/L) increased Ca2+ transient and cell shortening from (210+/-49) and (3.0+/-0.8) micron to (245+/-47) and (3.6+/-1.0) micron, respectively (P<0.05) in normal cardiomyocytes and from (196+/-54) and (3.0+/-1.3) micron to (240+/-49) and (3.6+/-1.3) micron respectively (P<0.05) in hypertrophied cardiomyocytes, while did not change calcium sensitivity in both groups. KB-R7943 completely blocked the activating effects induced by E-4031 in both of normal and hypertrophied cardiomyocytes. Nicardipine did not block the increasing effects of E-4031., Conclusion: E-4031 increased Ca2+ transient and cell contraction via stimulating reverse mode of Na+/Ca2+ exchange while without influencing calcium sensitivity. These effects were more notable in hypertrophied cardiomyocytes than in normal myocytes.

The effects of 5-(N,N-dimethyl)amiloride (DMA) (a blocker of Na(+)/H(+) exchanger or Na(+)/Ca(2+) exchanger) on calcium transient and cell contraction in isolated ventricular myocytes in normal rats and rats with myocardial hypertrophy were examined using ion imaging system with a charge coupled digital camera (CCD camera). Loading myocytes with Fura-2, electrically triggered Ca(2+) transients and cell shortening were measured simultaneously. The results showed that 10 micromol/L DMA increased Ca(2+) transient and cell shortening from 209.60+/-54.96 and 3.07+/-0.97 micrometer to 238.50+/-80.41 and 4.07+/-1.02 micrometer, respectively (P<0.05), which was completely abolished by application of KB-R7943, a specific reverse mode Na(+)/Ca(2+) exchanger blocker. After blocking L-type Ca(2+) channels by nicardipine, DMA also enhanced Ca(2+) transient and cell shortening. In rats with myocardial hypertrophy, DMA showed the common pharmacologic profile as in normal rats but more intense stimulating effects on Ca(2+) transient and cell contraction. The results suggest that DMA increase Ca(2+) transient and cell contraction via stimulating reverse mode Na(+)/ Ca(2+) exchange, and the stimulating effect is more pronounced in rats with myocardial hypertrophy than in normal ones.