CONTINUAL ELECTRIC-FIELD STIMULATION PRESERVES CONTRACTILE FUNCTION OF ADULT VENTRICULAR MYOCYTES IN PRIMARY CULTURE

To model with greater fidelity the electromechanical function of fresh ly isolated heart muscle eels in primary culture, we describe a techni que for the continual electrical stimulation of adult myocytes at phys iological frequencies for several days. A reusable plastic cover was c onstructed to fit standard, disposable 175-cm(2) tissue culture flasks and to hold parallel graphite electrodes along the long axis of each flask, which created a uniform electric field that resulted in a captu re efficiency of ventricular myocytes of 75-80%. Computer-controlled a mplifiers were designed to be capable of driving a number of flasks co ncurrently, each containing up to 4 x 10(6) myocytes, over a range of stimulation frequencies (from 0.1 to 7.0 Hz) with reversal of electrod e polarity after each stimulus to prevent the development of pH gradie nts around each electrode. Unlike quiescent, unstimulated myocytes, th e amplitude of contraction, and velocities of shortening and relaxatio n did not change in myocytes paced at 3-5 Hz for up to 72 h. The maint enance of normal contractile function in paced myocytes required mecha nical contraction per se, since paced myocytes that remained quiescent due to the inclusion of 2.5 mu M verapamil in the culture medium for 48 h also exhibited a decline in contractility when paced after verapa mil removal. Similarly, pacing increased peak calcium current compared with quiescent cells that had not been paced. Thus myocyte contractio n at physiological frequencies induced by continual uniform electric f ield stimulation in short-term primary culture in defined medium maint ains some biophysical parameters of myocyte phenotype that are similar to those observed in freshly isolated adult ventricular myocytes.