Simultaneous measurement of intracellular calcium and ventricular function in the phospholamban-deficient mouse heart

We describe the procedure for the measurement of intracellular calcium (Ca-i(2+)) simultaneously with function in the intact mouse heart and report findings in phospholamban-deficient mice. Seven phospholamban-deficient and six age-matched wild-type hearts were perfused retrogradely with oxygenated Krebs-Henseleit solution. Aequorin was injected into the apex of five hearts from each group to characterize Ca-i(2+) transients. A pressure-sensing balloon was positioned in the left ventricle. Peak Ca-i(2+) was significantly greater in the phospholamban-deficient hearts than in wild-type hearts (0.98 +/- 0.07 vs. 0.78 +/- 0.09 mu M, p<0.05), Calcium exchange was significantly faster in the phospholamban-deficient hearts. Ca-i(2+) transients of significantly increased amplitude and decreased duration in phospholamban-deficient hearts correlated with increased contractility and faster relaxation. We report the first recordings of intracellular calcium transients in the intact beating mouse heart and present direct evidence that phospholamban is a key regulator of basal Ca-i(2+) and contractility. (C) 1996 Academic Press, Inc.