The Na+/Ca2+ exchange inhibitor SEA0400 (up to 1 microM) failed to significantly alter diastolic intracellular Ca2+ or the amplitude of Ca2+ transients in isolated canine ventricular myocytes.
SEA0400 does not enhance Ca2+ transients or contractility in canine ventricular myocytes, likely due to its limited inhibitory effect on NCX and suppression of L-type Ca2+ current.
AIMS: This study was designed to evaluate the effects of the Na(+)/Ca(2+) exchange (NCX) inhibitor SEA0400 on Ca(2+) handling in isolated canine ventricular myocytes. METHODS AND RESULTS: Intracellular Ca(2+) (Ca(2+)(i)) transients, induced by either field stimulation or caffeine flush, were monitored using Ca(2+) indicator dyes. Ca(2+)(i)-dependent modulation of the inhibitory effect of SEA0400 on NCX was characterized by the changes in Ni(2+)-sensitive current in voltage-clamped myocytes. Sarcoplasmic reticulum (SR) Ca(2+) release and uptake were studied in SR membrane vesicles. Gating properties of single-ryanodine receptors were analysed in lipid bilayers. Ca(2+) sensitivity of the contractile machinery was evaluated in chemically skinned myocytes. In myocytes paced at 1 Hz, neither diastolic Ca(2+)(i) nor the amplitude of Ca(2+)(i) transients was significantly altered by SEA0400 up to the concentration of 1 microM, which was shown to inhibit the exchange current. The blocking effect of SEA0400 on NCX decreased with increasing Ca(2+)(i), and it was more pronounced in reverse than in forward mode operation at every Ca(2+)(i) examined. The rate of decay of the caffeine-induced Ca(2+)(i) transients was decreased significantly by 1 microM SEA0400; however, this effect was only a fraction of that observed with 10 mM NiCl(2). Neither SR Ca(2+) release and uptake nor cell shortening and Ca(2+) sensitivity of the contractile proteins were influenced by SEA0400. CONCLUSION: The lack of any major SEA0400-induced shift in Ca(2+) transients or contractility of myocytes can well be explained by its limited inhibitory effect on NCX (further attenuated by elevated Ca(2+)(i) levels) and a concomitant reduction in Ca(2+) influx due to the predominantly reverse mode blockade of NCX and suppression of L-type Ca(2+) current.
Birinyi et al. (Thu,) conducted a other in Isolated canine ventricular myocytes. SEA0400 was evaluated on Intracellular Ca2+ transients and contractility. The Na+/Ca2+ exchange inhibitor SEA0400 (up to 1 microM) failed to significantly alter diastolic intracellular Ca2+ or the amplitude of Ca2+ transients in isolated canine ventricular myocytes.