Contractile properties of isolated porcine ventricular myocytes

Abstract
Objective: The aim was to examine the structure, function, and inotropic responsiveness of isolated porcine myocytes. Methods: Left ventricular myocytes were harvested from six pigs with normal echocardiographic and pressure indices of left ventricular function: fractional shortening 30 (SEM 2)%, peak+dP/dt 1225(110) mm Hg·s−1, end diastolic pressure 7(2) mm Hg, and cardiac output 2.8(0.5) litres·min−1. Indices of myocyte contractility were examined using a computer assisted video edge detection system which included the percent and velocity of myocyte shortening. Myocyte contractions were recorded by alternating field stimulation at 1 Hz and measurements performed in the presence of 2-10 mM extracellular Ca2+. Contractile properties of isolated porcine myocytes were examined unattached (n=20) or following attachment to a basement membrane substrate (n=63). Results: Left ventricular myocytes were successfully obtained from all pigs with a 68% average yield of viable myocytes. Isolated myocyte length was 128(6) μm with an average profile surface area of 2226(51) μm2 (coefficients of variation of 25% and 35% respectively). Electron microscopic examination showed normal cytoarchitecture with 62(4)% myofibrils by volume. Baseline extent and velocity of shortening for unattached myocytes was 6.2% and 77(10) μm·s−1 respectively. Baseline extent and velocity of shortening for myocytes adherent to a basement substrate were 4.9(0.4)% and 64(7) μm·s−1. These indices of myocyte contractile function increased from baseline values for both the unattached and attached cells with increased extracellular Ca2+. Conclusions: Isolated porcine left ventricular myocytes retain normal cytoarchitecture and composition, respond to field stimulation, and are responsive to extracellular Ca2+. Myocytes adherent to a basement membrane substrate were capable of contracting against this resistive load. Cardiovascular Research 1993;27:304-311