Procaine in cardioplegia: The effect on EDHF-mediated function in porcine coronary arteries

Objectives: Hyperkalemia in cardioplegia impairs the endothelium-derived hyperpolarizing factor (EDHF)-mediated function. This study examined the effect of procaine in cardioplegia on the EDHF-mediated response in porcine coronary arteries. Methods: An isometric force study was performed in a myograph. Two rings taken from the same artery (diameter 200-450 mum) were incubated with Krebs solution (group I) or 20 mM K+ (group II) with/without procaine (1 mM) at 37degreesC for 1 hour. The EDHF-mediated relaxation was induced by bradykinin (BK, -10 similar to -6.5 log M) after U-46619 (-8 log M, in group I) or K+-precontraction (in group II) in the presence of indomethacin (7 muM), N-G-nitro-L-arginine (300 muM), and hemoglobin (20 muM). The membrane potential of a single smooth muscle cell was measured by a microelectrode after superfusion with Krebs solution with/without procaine for 1 hour. Results: The EDHF-mediated relaxation was increased by the treatment with procaine with the EC50 shifted leftward (97.3 +/- 0.6% vs. 83.0 +/- 5.1% at -7 log M and 99.4 +/- 0.6% vs. 96.7 +/- 1.6% at -6.5 log M, p < 0.05; EC50: -8.57 +/- 0.24 vs. -7.92 +/- 0.23 log M, p < 0.05). Procaine decreased the BK-induced hyperpolarization from -72.3 +/- 0.7 mV to -68.8 +/- 0.8 mV (-6.5 log M, p < 0.01). The EDHF-mediated relaxation in arteries exposed to 20 mM K+ was not altered by procaine (49.9 +/- 7.4% vs. 55.8 +/- 7.6%, p > 0.05). Conclusions: In the coronary arteries, procaine has a depolarizing effect but it enhances EDHF-mediated relaxation. Addition of procaine in cardioplegia did not change the EDHF-mediated endothelial function.