SARCOPLASMIC-RETICULUM CALCIUM-UPTAKE IN HUMAN MYOCARDIUM SUBJECTED TO ISCHEMIA AND REPERFUSION DURING CARDIAC-SURGERY

We evaluated the effect of ischemia and reperfusion on sarcoplasmic re ticulum Ca uptake in patients subjected to cardiac surgery. Our series included 16 patients (seven female, nine male, age 63 +/- 2 years): f ive were subjected to aortic valve replacement, five to aortic and mit ral valve replacement, six to coronary artery bypass graft. In each ca se no clinical, electrocardiographic or echocardiographic evidence of perioperative infarction was observed. Biopsies were obtained from the right atrium of each patient before starting extracorporeal circulati on, and after the recovery of spontaneous contractile activity i.e. af ter cardioplegia-ischemia-reperfusion. The tissue was homogenized, and oxalate-supported Ca uptake, which represents sarcoplasmic reticulum Ca uptake, was measured in the unfractionated homogenate. The assay wa s performed under basal conditions and in the presence of 900 mu M rya nodine, in order to block sarcoplasmic reticulum Ca release channels. Under basal conditions at pCa = 5.85 the rate of sarcoplasmic reticulu m Ca uptake averaged 4.76 +/- 0.37 nmol/min per mg of protein in the p re-ischemic samples, and decreased significantly in the post-ischemic samples (3.09 +/- 0.29 nmol/min per mg, P<0.01). A significant decreas e of Ca uptake after ischemia and reperfusion was observed also in the presence of ryanodine (3.53 +/- 0.48 nmol/min per mg) compared to pre -ischemic values (5.98 +/- 0.56 nmol/min per mg, P<0.01). Additional e xperiments showed no change in the Ca sensitivity of Ca uptake in the postischemic samples (K-Ca = 0.48 +/- 0.02 mu M, no significant differ ence after ischemia and reperfusion). In conclusion, active sarcoplasm ic reticulum Ca transport was impaired in human atrial myocardium afte r reversible ischemia and reperfusion. (C) 1996 Academic Press Limited