Inhibition by KB-R7943 of the Reverse Mode of the Na+/Ca2+ Exchanger Reduces Ca2+ Overload in Ischemic-Reperfused Rat Hearts.

Abstract

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

Impaired Ca2+ Handling in Perfused Hypertrophic Hearts from Dahl Salt-Sensitive Rats

“…A concentration of 70 mmol/l Na was chosen for use in the low-Na solution to prevent excessive increases in [Ca 2 ]i and the occurrence of ventricular fibrillation. We previously demonstrated the reproducibility of the resultant increase and decrease in the fluorescence ratio and the inhibitory effect of NCX blockade on the increase in the ratio during low-Na exposure (21). In this study, the time-to-peak and the decay-time of the diastolic fluorescence ratio were compared between the two strains.…”

“…The method for measuring fluorescence using an optic fiber probe and Ca analyzer (CAF-110, CA-200DP, Japan Spectroscopic Co., Tokyo, Japan; Power Lab, AD Instruments, Castle Hill, Australia) in the perfused heart has been described in detail previously (19)(20)(21). The hearts were perfused with loading Tyrode solution containing 4 µmol/l fura-2 acetoxymethyl ester (fura-2, Dojindo Laboratories, Kumamoto, Japan), a fluorescent ion indicator, for 30 min initially at low temperature (5 to 6°C) and finally at room temperature (23 to 26°C).…”

“…After 10 min of control perfusion, the hearts were exposed to the low-Na solution (70 mmol/l tris (hydroxymethyl) aminomethane (Tris), 70 mmol/l NaCl, 6 mmol/l KCl, 1 mmol/l MgCl2, 2 mmol/l CaCl2, 10 mmol/l HEPES, and 10 mmol/l glucose, gassed with 100% O2, maintained at pH 7.4 and at 37°C) for 2 min (first exposure). This procedure induces Ca 2 influx via the reverse mode of NCX and Ca 2 release from the SR (18,21,22). After returning to the standard Tyrode solution, the perfusate was switched to a Tyrode solution containing 10 mmol/l caffeine for 3 min to induce Ca 2 release from the SR and deplete SR Ca 2 (23).…”

Difference in the Cardioprotective Mechanisms Between Ischemic Preconditioning and Pharmacological Preconditioning by Diazoxide in Rat Hearts

“…Although the reason why the reduction in acidification contributes to cardioprotection remains elusive, ischemic acidification per se can cause increased fragility and permeability of the mitochondrial membrane 38 and impairment of the mitochondrial respiratory chain. 39 On reperfusion, Ca 2+ overload through the Na + /H + and Na + /Ca 2+ exchangers 40 and increased opening probability of the mitochondrial permeability transition pores 41 may be involved in myocardial damage.…”

Caldaret, an Intracellular Ca2+ Handling Modulator, Limits Infarct Size of Reperfused Canine Heart

“…-overload by NHE inhibition (4,5) or NCX inhibition (6,7) has been demonstrated to improve cardiac function, to decrease the incidence of arrhythmia, and to decrease infarct size during ischemia and reperfusion. However, inhibition of L-type Ca 2+ -channels, another potential pathway of Ca 2+ influx, failed to reduce myocardial injury when Ca…”