Objective: Inhibition of Na(+)-H(+) exchange (NHE) delays the onset of myocardial rigor contracture during ischemia. The aim of this study was to analyse the effects of NHE inhibition on cell-to-cell electrical uncoupling during myocardial ischemia/reperfusion.
Methods: Twenty-six isolated rat hearts and 23 in situ porcine hearts were submitted to no-flow ischemia followed by reperfusion, with or without pre-treatment with cariporide (7 microM in rats and 3 mg/kg in pigs). Ischemic rigor and hypercontracture, conduction velocity and myocardial electrical impedance were monitored.
Results: Pre-treatment with cariporide delayed ATP depletion (luminescence assay in rat myocardium) and onset of rigor contracture (tension recordings or ultrasonic crystals) during ischemia both in rat and pig hearts (P<0.05). In addition, cariporide delayed the onset of sharp changes in tissue resistivity and phase angle in impedance recordings (four-electrode probes) from 10+/-1 to 13+/-1 min (P<0.001) in rat hearts, and from 22+/-1 to 38+/-2 min (P<0.001) in pigs. Blockade of impulse propagation (transmembrane action potentials in rat hearts) was also markedly delayed by cariporide (from 14+/-1 to 20+/-1 min, P<0.001). Reperfusion-induced LDH release in rat hearts and infarct size in pigs were markedly reduced by pre-treatment with cariporide.
Conclusions: Inhibition of NHE with cariporide slows the progression of ischemic injury during myocardial ischemia, and delays the onset of cell-to-cell electrical uncoupling.