MYOCARDIAL PROTECTION AND POTASSIUM MOVEMENT

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Myocardial ischemia results in intracellular ionic imbalance (Na<@D1+@>D1 overload ; K<@D1+@>D1 loss). We hypothesize that warm oxygenated blood cardioplegia (warm OBC) in the post-ischemic myocardium, incresing myocardial oxygen consumption (VO<@D22@>D2), may enhance Na<@D1+@>D1/K<@D1+@>D1 pump activity, which could contribute to recovery from the intracellular ionic imbalance. To test this, we determined temperature dependency of Na<@D1+@>D1/K<@D1+@>D1 pump activity and investigated the relationship between VO<@D22@>D2 and cation movement during warm OBC in cardiac surgery. Methods : (A) ouabain sensitive current (Ip) was measured at 18ﾟ, 28ﾟ, and 28ﾟC by whole-cell clamp technique (ramp : +50--130 mV) using Guinea-pig ventricular myocytes. (B) 44 patients undergoing cardiac surgery received OBC every 30 min at 18ﾟC and finally at 35ﾟ-37ﾟC (Na<@D1+@>D1 : 134.8(]SY.+-。[)0.4 ; K<@D1+@>D1 : 18.7(]SY.+-。[)0.1 mmol/L). During the infusion of the final warm OBC,the coronary effluent was sa … More mpled (5-8 different points/patient) from the coronary sinus (CS). Na<@D1+@>D1 or K<@D1+@>D1 movement was assessed by its concentration difference ( [cation] <@D2CS@>D2 minus [cation] <@D2OBC@>D2) and VO<@D22@>D2 by the difference of oxygen content between the OBC solution and the CS effluent. Cation movement efficiency (Ek, K<@D1+@>D1 movement per unit volume of VO<@D22@>D2) was assessed by calculating a slope using linear regression analysis in the K<@D1+@>D1 movement-VO<@D22@>D2 relationship. Results : (A) Ip was greater at 37ﾟC than at 18ﾟC (114.3(]SY.+-。[)17.2 vs 22.7(]SY.+-。[)1.2 pA at -40 mV,respectively). (B) The greatre VO<@D22@>D2 was associated with the greater positive value of the [Na<@D1+@>D1] difference and the greater negative value of the [K<@D1+@>D1] difference, suggesting energy dependent transsarcolemmal cation movement(outward Na<@D1+@>D1 ; inward K<@D1+@>D1)during the final warm OBC.Ek (0.227-0.019 mmol/ml O<@D22@>D2) decreased with prologation of the ischemic period (23-214 min). Conclusion : There may be energy dependent cation movement during oxygenated cardioplegia, contributing to recovery of the myocardium from the intracellular Na<@D1+@>D1 overload and K<@D1+@>D1 loss. Prolongation of the ischemic period might reduce the effeciency between myocardial oxygen consumption and cation movement. Less