Spontaneous Oscillatory Contraction (SPOC): Quantifying the Contractile Performance of Human Cardiomyocytes

Abstract

SPontaneous Oscillatory Contraction (SPOC) describes repetitive cycles of rapid lengthening (relaxation) and slow shortening (contraction) observed in small bundles of striated muscle cells (myocytes). SPOCs can be induced in both skeletal and cardiac muscles. Here we describe SPOCs in human cardiac muscle, and in particular focus on SPOCS from left ventricles. All samples were frozen in liquid N either within minutes of the loss of the blood supply to the heart (i.e. soon after the aorta was clamped), or within four hours of surgical removal of non-failing hearts that were perfused with cardioplegic solution, thus reducing post-mortem damage to inhibit spontaneous contractions. SPOC is best considered as a third state that is intermediate to contraction and relaxation. SPOC frequency (SPOC period) and shortening velocities correlate well body size in various animals thus, SPOC is likely to reflect the physiology of the heart as it functioned in life. Tiny samples (<1 mg) of human immobilized cardiomyocytes are exposed to precise ionic conditions to induce SPOC. SPOC cycles are recorded at 25 frames per second in bright field yielding high spatial and temporal resolution information. Measurements of the mean rates of shortening (systole) and lengthening (diastole), and of the SPOC periods enable us to determine if SPOC parameters change with age in non-failing human heart samples. We have examined non-failing heart left ventricular samples using donors from ages 3 weeks to 65 years. These hearts exhibit a range of heart rates that correlate with donor age. We also used the SPOC technique to identify functional defects in samples from patients diagnosed with hypertrophic cardiomyopathy (HCM) who had undergone cardiomyectomy of the enlarged interventricular septum. We only examined patients with known genetic mutations in cardiac sarcomeric genes.