Na-H exchange inhibition with cariporide limits functional impairment caused by repetitive ischemia

Intracellular calcium ([Ca]i) overload on reperfusion may be one of the mechanisms responsible for ischemia-induced regional myocardial dysfunction. Because inhibiting the Na-H exchanger (NHE) limits intracellular sodium ([Na]i) and subsequent [Ca]i accumulation, we hypothesized that NHE inhibition would attenuate regional dysfunction in response to 25 cycles of ischemia (I, 2-min) and reperfusion (R, 8-min) of the left circumflex coronary artery (LCx) in conscious swine. Six animals were instrumented to measure arterial pressure, regional myocardial blood flow (colored microspheres), systolic wall thickening (WTh) in the normally perfused (left anterior descending, LAD) and LCx regions (sonomicrometry), LCx blood flow velocity (Doppler), and to reversibly occlude the LCx (hydraulic occluder). Each animal completed three protocols separated by 7 days: ISC, 25 I/R cycles; CAR, 25 I/R cycles + NHE inhibition (cariporide); and VEH, vehicle administration for 4.2 h. Regional myocardial blood flow was measured during LCx occlusion in the first protocol and 10 min after I/R 25 in all protocols. Systemic hemodynamics were similar among and within each protocol. Blood flow measured during LCx occlusion confirmed that perfusion was reduced (p < 0.05) to this compared with the LAD region. During ISC, LCx WTh was reduced (p < 0.05) after five IR cycles, and a stable reduction (approximately 55% of baseline; p < 0.05) was present after 20 I/R cycles. During CAR, LCx systolic WTh was reduced (p < 0.05) only after 15 and 25 I/R cycles (approximately 80 and 72%, respectively). The decrease in LCx WTh was greater in ISC than in CAR (p < 0.05). LCx WTh was not altered during VEH, while LAD WTh was similar within and among all protocols. Regional blood flow measured after 25 I/R cycles was not different among protocols. Our results indicate that NHE inhibition delays the onset and limits the degree of regional dysfunction in response to repeated bouts of ischemia and reperfusion.