Enhancement of calcium cycling by atrial sarcoplasmic reticulum after cardiopulmonary bypass and cardioplegia during open heart surgery.

We studied myocardial Ca2+ cycling during cardiopulmonary bypass and cold-blood cardioplegia (CPB/CBC) in patients with coronary heart disease undergoing coronary artery bypass grafting. Right atrial biopsies were taken from 13 patients before and after CPB/CBC: after pericardiotomy, immediately after aortic cross-clamp removal, and following termination of CPB/CBC. Changes in ionized Ca2+ concentration (nM) were monitored with indo 1 during Ca2+ uptake and Ca2+ release by sarcoplasmic reticulum in a medium containing 1% homogenized myocardium. Ryanodine inhibition was used to estimate Ca2+ release channel activity. With CPB/CBC, the initial Ca2+ concentration of reaction media increased 33%, (962 +/- 150 to 1262 +/- 106 nM; mean +/- SD). Ca2+ cycling increased asymmetrically, 108% for Ca2+ uptake (3.91 +/- 1.32 to 8.15 +/- 3.17 nM/s), 197% for Ca2+ release (0.90 +/- 0.80 to 2.73 +/- 1.13 nM/s), and 68% for the ratio of Ca(2+)-release to Ca(2+)-uptake activities (0.22 +/- 0.14 to 0.37 +/- 0.13). The dissociation constant of the Ca2+ pump for Ca2+ was unaltered by CPB/CBC (289 +/- 76 nM). During the time period that was studied post-bypass, Ca(2+)-pump activity remained increased, although the Ca(2+)-channel activity returned to pre-bypass values (all p < 0.05). We conclude that CPB/CBC produces increased myocardial Ca2+ load, twofold increased Ca2+ uptake, and threefold increased Ca2+ release by sarcoplasmic reticulum.