CHARACTERIZATION OF A HYPERPOLARIZATION-ACTIVATED CURRENT IN DEDIFFERENTIATED ADULT-RAT VENTRICULAR CELLS IN PRIMARY CULTURE

1. The presence of a hyperpolarization-activated pacemaker (I-f)-like current was tested in dedifferentiated adult rat ventricular myocytes up to 12 days in primary culture with the whole-cell patch clamp techn ique. 2. An I-f-like current was found and characterized on freshly is olated and cultured ventricular cells. Both activation and density of the current varied in relation to the stage of dedifferentiation. The current was activated from -92.0 +/- 2.5 and -63.0 +/- 1.0 mV at the b eginning (4-day-cultured cells) and end of the dedifferentiation proce ss (12 days), respectively. Its density measured at -170 mV progressiv ely increased from -2.34 +/- 0.36 to -6.12 +/- 0.64 pA pF(-1) between the two farthest stages of cellular remodelling. In freshly isolated c ells the current was activated at -108.0 +/- 1.5 mV and its current de nsity measured at -170 mV was -1.97 +/- 0.56 pA pF(-1). 3. The current was blocked by extracellular CsCl (3 mM) in a voltage-dependent manne r. Modification of reversal potentials obtained at various values of [ K+](o) (5.4 or 25 mill) and [Na+](o) (140 or 30 mM) suggests that the current was carried by both K+ and Na+ ions. 4. It is concluded that t he hyperpolarization-activated inward current, recorded in freshly iso lated and in cultured ventricular cells has characteristics similar to those of I-f. In adult rat ventricular cells it is activated in a non -physiological potential range, but can be elicited in a more physiolo gical range when the cells are remodelled through a dedifferentiated w ay. It is suggested that such a current could be implicated in ventric ular arrhythmias developed in pathological events.