Increased resistance to myocardial ischemia in the Brown Norway vs. Dahl S rat: role of nitric oxide synthase and Hsp90

Hearts from Brown Norway (BN/Mcw) rats are more resistant to ischemia than hearts from Dahl S (SS/Mcw) rats. We determined whether nitric oxide (·NO) is responsible for increased cardioprotection in BN/Mcw vs. SS/Mcw hearts. Hearts from the two strains were treated with NG-monomethyl-l-arginine (l-NMA) or S-nitrosoglutathione (GSNO) before ischemia and reperfusion. Infarct size in untreated BN/Mcw hearts was ~63% less than in SS/Mcw hearts. Inhibiting NOS with l-NMA increased infarct size in BN/Mcw hearts to that observed in untreated SS/Mcw hearts but did not further increase injury in SS/Mcw hearts. The ·NO donor GSNO decreased infarct size in SS/Mcw rats but had no effect on BN/Mcw hearts. Plasma and heart tissue from BN/Mcw rats contained 80% and 130% more nitrite + nitrate than that from SS/Mcw rats. These data suggest that increased ·NO production protects BN/Mcw hearts from ischemic injury. Real time PCR showed no differences in NOS1, NOS2 or NOS3 isozyme transcripts in the hearts from the two strains. NOS3 was the only isozyme detected by western analysis. Both strains exhibited the same level of NOS3 and hsp90 protein expression. However, hsp90 association with NOS3 in BN/Mcw hearts was increased twofold compared with SS/Mcw hearts. Inhibiting hsp90-NOS3 interaction with geldanamycin decreased the resistance to ischemia in BN/Mcw hearts but not in SS/Mcw hearts. SS/Mcw hearts also generated three times more Nω-nitro-l-arginine-methylester inhibitable superoxide than BN/Mcw hearts. These findings indicate that hsp90 with NOS3 increases ·NO production and decreases uncoupled NOS3 activity. We conclude increased association of hsp90 with NOS3 is a major mechanism by which BN/Mcw hearts are more resistant to ischemia than SS/Mcw hearts.