The objective of this study was to determine if prior exposure of rat hearts to
S-nitrosocysteine (CysNO) was able to provide protection against
reperfusion injury. We probed NO release using the extracellular NO scavenger
oxyhemoglobin (oxyHb), and we examined the involvement of the
amino acid transport system L (L-AT), a known transporter of CysNO, using the L-AT competitor,
L-leucine (L-Leu). Isolated (9- to 12-week-old Wistar male) rat hearts (six to eight per group) were perfused with CysNO (10 microM) for 30 min with or without the L-AT competitor L-Leu (1 mM) before 30 min of
ischemia. Cardiac function was assessed before, during, and
after treatment and during 120 min of reperfusion after
ischemia. Functional recovery (rate-pressure product) was significantly improved in the CysNO group compared to hearts in the CysNO+L-Leu group and the control group (p<0.05).
Necrosis, measured by
triphenyltetrazolium chloride staining, was significantly reduced in CysNO hearts (p<0.05) and this improvement was reversed by L-Leu. The NO scavenger oxyHb (20 microM) was perfused either concomitant with CysNO or just before
ischemia. In neither case did oxyHb affect the cardioprotection afforded by CysNO. OxyHb alone, given in either time window, did not alter the course of
ischemia-reperfusion injury. When
nitrite was used in place of CysNO, no protective effects were observed. Perfusion with CysNO increased tissue
S-nitrosothiol (RSNO) levels from an unmeasurable background to a value of about 15.7+/-4.1 pmol RSNO/mg
protein, as measured by triiodide-based chemiluminescence in the presence and absence of
mercury(II)
chloride. In the presence of L-Leu, this value dropped to 0.4+/-0.3 pmol RSNO/mg
protein. This study demonstrates that exposure to CysNO before
ischemia increases tissue
S-nitrosothiol levels, improves postischemic contractile dysfunction, and attenuates
necrosis. The mechanism of cardioprotection requires the uptake of CysNO via the L-AT and does not seem to involve NO release either during CysNO exposure or during
ischemia. This suggests that the protective effects of CysNO are mediated through the posttranslational modification of cellular
proteins through an NO-independent transnitrosation mechanism.