ADULT-RAT VENTRICULAR MYOCYTES CULTURED IN DEFINED MEDIUM - PHENOTYPEAND ELECTROMECHANICAL FUNCTION

We studied primary short-term cultures of adult rat ventricular myocyt es in defined medium to determine whether phenotype and electromechani cal function are maintained in rod-shaped, quiescent cells. Although > 80% of the myocytes retained their rod-shaped in vivo morphology for u p to 72 h, contractile function as measured by cell edge motion declin ed 30-50% from 6 to 24 h, paralleling a 68% shortening of action poten tial duration. From 24 to 72 h, contractility remained unchanged. Ca2 channel current density increased 55% after 24-48 h and then returned to the level of freshly isolated cells (9 +/- 1 pA/pF, mean +/- SE). Resting membrane potential (-71 +/- 1 mV) and action potential oversho ot (34 +/- 3 mV) did not change. The ratio of alpha- to beta-myosin he avy chain mRNA and the level of cardiac alpha-actin mRNA were maintain ed for 8 days. Thus quiescent adult rat ventricular myocytes in define d medium undergo extensive phenotypic adaptation within 72 h of isolat ion, despite maintenance of a rod-shaped morphology and stable levels of contractile protein mRNA, which may limit their suitability for ele ctrophysiological and contractile function studies.