Effect of multi-dose cardioplegia and cardioplegic solution buffering on myocardial tissue acidosis

62 X-RAY MICROANALYSIS OF INTRACELLULAR CALCIUM IN THE RAT MYOCARDIUM. Harley D. Sybers, Martha V. Myre and Christopher D. Myre. Baylor College of Medicine, Houston, TX 77030 Intracellular calcium concentration in the cytoplasm and mitochondria of cardiac cells was determined by x-ray Energy Dispersive Spectrometry (EDS). Hearts were rapidly excised from anesthetized rats and tissue obtained from the left ventricle was rapidly frozen in a graphite-liquid nitrogen slush. Frozen sections (500-1OOOA) were cut on an LKB ultramicrotome with cryo-kit. The frozen sections were sublimated under vacuum and analysed in a Jeol 1OOC electron microscope with a Kevex EDS. Occasional mitochondria contained dense granules with high levels of calcium and in occasional mitochondria no calcium was detected. Generally, however, mitochondria contained significantly higher levels (5.77 + .07 mmol/kg) of calcium than the cytoplasm (0.99 + .05). We conclude that mitochondria normally modulate intracellular calcium levels maintaining homeostasis of cytoplasmic calcium. Table: Calcium content, mmol/kg Mitochondria Cytoplasm .53 + .Ol (N=5) 1. 1.12 + .03 (N=6) 2. .37 T .Ol (N=15) .30 + .OO (N=15) 3. 6.0 7 1.00 (N=24) 1.15 + .15 (N=23)** 4. 6.7 + 1.10 (N=21) 1.56 + .16 (N=14)* 5. 12.1 + 1.0 (N=13) 1.10 + .05 (N=8)" *P < .05;-**P < .OOl; N = number of mitoch%dria or cytoplasmic areas analysed. (Supported by USPHS NIH Grant HL 21218).

EFFECT OF MULTI-DOSE CARDIOPLEGIA AND CARDIOPLEGIC SOLUTION BUFFERING ON MYOCARDIAL TISSUE ACIDOSIS. Gordon A.Tait, Peter D.Booker, Gregory J.Wilson, John G.Coles, David J.Steward and David C.MacGregor. Cardiovascular Laboratories, Banting Institute, University of Toronto, Toronto, Ont., Canada M5G lL5 This study was conducted to assess the effect of multi-dose infusion of three different types of cardioplegic solution on tissue acidosis during global myocardial ischemia. The solutions tested were l)a conventional crystalloid potassium cardioplegic solution buffered with sodium bicarbonate, 2)a blood based cardioplegic solution and 3)Bretschneider's solution (a crystalloid solution strongly buffered with histidine). The buffering capacity of solutions 2 and 3 was 40 and 60 times, that of solution 1. In each group, 5 dogs were respectively, placed on cardiopulmonary bypass and the aorta cross clamped for 3 hours with the heart maintained at 20°C. Cardioplegic solution at 20°C was infused with an initial dase of 500ml and a supplementary dose of 250ml every 30min. Myocardial tissue pH was measured with a glass needle electrode throughout the period of arrest. The average myocardial tissue pH at the end of the 3 hours of ischemia was 6.542 0.07 in Group 1,7.23 3 0.05 in Group 2 and 7.192 0.06 in Group 3. The pII in Group 1 was significantly (p