Postischemic deterioration of sarcoplasmic reticulum: Warm versus cold blood cardioplegia

Abstract

Impaired cardiac sarcoplasmic reticulum (SR) function, as evidenced by reduced SR Ca 2+ uptake rate and decreased SR Ca 2+-adenosine triphosphatase activity, has been found in postischemic “stunned” myocardium and in hearts subjected to hypothermic arrest. In this study, we compared the effects of retrograde continuous coronary sinus warm blood cardioplegia (WBC) and retrograde intermittent cold blood cardioplegia (CBC) on cardiac SR function and postischemic ventricular functional recovery in pig hearts. Twelve in situ isolated pig hearts supported by cardiopulmonary bypass were subjected to 120 minutes of cardioplegic arrest with either WBC (37 °C or CBC (6 ° to 10 °C), followed by 60 minutes of 37 °C reperfusion. Left ventricular global contractile function and coronary blood flow were measured before arrest and during reperfusion. Cardiac SR was isolated from left ventricular biopsy specimens, and 45Ca 2+ uptake by SR and SR Ca 2+-adenosine triphosphatase activity were determined. The recovery of left ventricular global contractile function as indicated by the maximum of the first derivative of left ventricular pressure was significantly improved in the WBC group compared with that of the CBC group (70% versus 46%; P < 0.05). The SR Ca 2+-adenosine triphosphatase activity was better preserved after 60 minutes reperfusion in WBC compared with CBC (0.31 ± 0.02 versus 0.20 ± 0.03 μM Pi/min/mg protein, p < 0.05), and the recovery of SR Ca 2+ uptake was significantly improved by WBC compared with CBC (1.15 ± 0.12 versus 0.83 ± 0.04 μM Ca 2+/min/mg protein; p < 0.05). These results indicate that the superiority of continuous WBC over intermittent CBC in promoting functional recovery may be related to its ability to improve postischemic SR function, which presumably plays a crucial role in regulating cellular Ca 2+ homeostasis.