Contractile properties of isolated porcine ventricular myocytes.

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) microns with an average profile surface area of 2226(51) microns 2 (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) microns.s-1 respectively. Baseline extent and velocity of shortening for myocytes adherent to a basement substrate were 4.9(0.4)% and 64(7) microns.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.