Effect of SEA0400, a novel inhibitor of sodium-calcium exchanger, on myocardial ionic currents

Abstract

The effects of 2-[4-[(2,5-difluorophenyl) methoxy]phenoxy]-5-ethoxyaniline (SEA0400), a newly synthesized Na(+)-Ca(2+) exchanger (NCX) inhibitor, on the NCX current and other membrane currents were examined in isolated guinea-pig ventricular myocytes and compared with those of 2-[2-[4-(4-nitrobenzyloxy) phenyl]ethyl]isothiourea (KB-R7943). SEA0400 concentration-dependently inhibited the NCX current with a 10 fold higher potency than that of KB-R7943; 1 microM SEA0400 and 10 microM KB-R7943 inhibited the NCX current by more than 80%. KB-R7943, at 10 microM, inhibited the sodium current, L-type calcium current, delayed rectifier potassium current and inwardly rectifying potassium current by more than 50%, but SEA0400 (1 microM) had no significant effect on these currents. These results indicate that SEA0400 is a potent and highly selective inhibitor of NCX, and would be a powerful tool for further studies on the role of NCX in the heart and the therapeutic potential of its inhibition.

Figure 1

Effect of SEA0400 and KB-R7943 on NCX. NCX current was elicited by ramp voltage clamp pulses at a frequency of 0.1 Hz. A and B: time course of the effects of 1 mM SEA0400 (A) and 10 mM KB-R7943 (B). C and D: superimposed records of the Ni²⁺-sensitive NCX current in the absence (a-b) and presence (c-d) of SEA0400 (C) and KB-R7943 (D). E: concentration-response relationships for the inhibitory effects of SEA0400 and KB-R7943 on inward and outward NCX current measured at −80 mV and +30 mV respectively. Symbols with bars indicate the mean±s.e.m. from three to four experiments.

Figure 2

Effect of SEA0400 and KB-R7943 on Na⁺ current. A and B: superimposed current records on depolarization to −20 mV from a holding potential of −90 mV in the absence and presence of 1 mM SEA0400 (A) and 10 mM KB-R7943 (B). Arrows indicate zero current level. C and D: current-voltage relationships in the absence and presence of SEA0400 (C) and KB-R7943 (D). Symbols with bars indicate the mean±s.e.m. from four experiments.

Figure 3

Effect of SEA0400 and KB-R7943 on Ca²⁺ and K⁺ currents. A and B: superimposed current records on depolarization to 10 mV from a holding potential of −40 mV in the absence and presence of 1 mM SEA0400 (A) and 10 mM KB-R7943 (B). Arrows indicate zero current level. C and D: current-voltage relationships in the absence and presence of SEA0400 (C) and KB-R7943 (D). Symbols with bars indicate the mean±s.e.m. from four experiments.

Figure 4

Effect of SEA0400 and KB-R7943 on delayed rectifier K⁺ current. A and B: superimposed current records on depolarization to 50 mV and return to the holding potential of −30 mV in the absence and presence of 1 mM SEA0400 (A) and 10 mM KB-R7943 (B). Arrows indicate zero current level. C and D: current-voltage relationships for the peak tail current in the absence and presence of SEA0400 (C) and KB-R7943 (D). Symbols with bars indicate the mean±s.e.m. from four experiments.

Figure 5

Summarized effects of SEA0400 and KB-R7943 on myocardial ionic currents. The inward and outward NCX currents at −80 mV and +30 mV, respectively, sodium current at −20 mV, L-type Ca²⁺ current at +10 mV, inward rectifying potassium current at +60 mV and delayed rectifier potassium current were measured as described in the text and inhibition of current amplitudes in the presence of SEA0400 (1 μM) and KB-R7943 (10 μM) were expressed as percentages of the value in the absence of compounds.