Publication No. 85-23, revised 1996). Adult male Sprague-Dawley rats weighing 300-350 g were anesthetized with pentobarbital Na (30 mg/kg, ip). The heart was quickly isolated and the aorta was cannulated for retrograde Langendorff perfusion. N-2-hydroxy-ethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered Tyrode solution (140 mmol/L NaCl, 6 mmol/L KCl, 1 mmol/L MgCl2, 2 mmol/L CaCl2, 10 mmol/L HEPES, 10 mmol/L J 2002; 66: 390 -396 (Received September 28, 2001; revised manuscript received January 9, 2002; accepted January 11, 2002 ]i dynamics and left ventricular pressure were monitored in perfused beating hearts. The effects of KB-R7943 (KBR), a selective inhibitor of the NCX in the reverse mode, were analyzed during low-Na + exposure and ischemia -reperfusion. Hearts from Sprague-Dawley rats were retrogradely perfused and loaded with 4 mol/L fura-2 to measure the fluorescence ratio as an index of [Ca 2+ ]i. To evaluate KBR effects on the reverse mode exchanger, the increase in [Ca 2+ ]i induced by low-Na + exposure (Na + : 30 mmol/L, 10 mmol/L caffeine pre-treatment) was measured with and without 10 mol/L KBR (n=5). In another series, the hearts were subjected to 10 min of low-flow ischemia with pacing, followed by reperfusion in the absence (n=6) or in the presence of 10 mol/L KBR (n=6). Background autofluorescence was subtracted to estimate the ratio in the ischemia -reperfusion protocol. KBR significantly suppressed the increase in [Ca 2+ ]i induced by low-Na + (40.2±11.2% of control condition, p=0.014), as well as on increase in diastolic [Ca 2+ ]i during ischemia (% increase from pre-ischemia in [Ca 2+ ]i at 10 min: KBR, 17.9±6.4%; no KBR, 44.4±7.7%; p=0.024). After reperfusion, diastolic [Ca 2+ ]i normalized more rapidly in KBR-treated hearts (% increase at 1 min: KBR, 4.5±7.0%; no KBR, 39.8±12.2%; p=0.03). Treatment with KBR also accelerated recovery of the rate -pressure product on reperfusion (1 min: KBR, 8,944±1,554 min -1 ·mmHg; no KBR, 4,970±1,325; p<0.05). Thus, inhibition of the reverse mode exchanger by KBR reduced ischemic Ca 2+ overload and possibly improved functional myocardial recovery during reperfusion in a whole heart model. (Circ J 2002; 66: 390 -396)
Circ