PRIMARY CULTURE OF HUMAN ATRIAL MYOCYTES IS ASSOCIATED WITH THE APPEARANCE OF STRUCTURAL AND FUNCTIONAL-CHARACTERISTICS OF IMMATURE MYOCARDIUM

We examined changes in the structural and physiological characteristic s of human atrial myocytes during primary culture in the presence of s erum. Action potentials and ionic currents were recorded in freshly di ssociated (FM) and cultured (CM) whole-cell patch-clamped myocytes. al pha-smooth muscle actin, sarcomeric a-actinin and P-myosin heavy chain s (beta-MHC) were stained with monoclonal antibodies. From day 5 to da y 21, myocytes lost their rod shape, spread and exhibited reorganized sarcomeres. These morphological chances were associated with a marked increase in membrane capacitance (+266%). Both beta-MHC and a-smooth m uscle actin were expressed in CM but not in FM, indicating a dediffere ntiation process. CM were characterized by a lower resting potential ( -30+/-2 v -60 +/- 4 mV, P<0.05) and, when repolarized, by a shorter ac tion potential duration (APD) than FM (APD-60: 126.9 v 159.6 ms. P<0.0 5). The inward rectifier K+ current was absent in CM, thus explaining the low resting potential. The density of the transient component of t he voltage-activated K+ current I-omega 1 was not modified during cult ure, while that of the sustained component I-SUS was increased fourfol d. The amplitude of I-Ca was increased, but its density was unchanged, indicating that CM maintained a normal density of functional calcium channels. Neither the voltage dependence nor the inactivation of I-Ca was modified in CM. The time constants of inactivation of I-Ca were un changed, although the amplitude of the rapidly inactivating component of I-Ca was increased in CM compared to FM. Moreover, I-Ca was increas ed by the beta-adrenergic agonist isoproterenol (1 mu M) throughout th e culture period. Our results demonstrate that in long-term serum-supp lemented culture, adaptation of human atrial myocytes to their new env ironment is associated with differential alterations of the main ionic currents and phenotypic changes characteristic of immature myocardium . (C) 1997 Academic Press Limited.