Characterization of a hyperpolarization‐activated current in dedifferentiated adult rat ventricular cells in primary culture

Abstract

The presence of a hyperpolarization‐activated pacemaker (If)‐like current was tested in dedifferentiated adult rat ventricular myocytes up to 12 days in primary culture with the whole‐cell patch clamp technique. An If‐like current was found and characterized on freshly isolated 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 beginning (4‐day‐cultured cells) and end of the dedifferentiation process (12 days), respectively. Its density measured at ‐170 mV progressively 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 cells the current was activated at ‐108.0 ± 1.5 mV and its current density measured at ‐170 mV was ‐1.97 ± 0.56 pA pF−1. The current was blocked by extracellular CsCl (3 mM) in a voltage‐dependent manner. Modification of reversal potentials obtained at various values of [K+]o (5.4 or 25 mM) and [Na+]o (140 or 30 mM) suggests that the current was carried by both K+ and Na+ ions. It is concluded that the hyperpolarization‐activated inward current, recorded in freshly isolated and in cultured ventricular cells has characteristics similar to those of If. In adult rat ventricular cells it is activated in a non‐physiological potential range, but can be elicited in a more physiological range when the cells are remodelled through a dedifferentiated way. It is suggested that such a current could be implicated in ventricular arrhythmias developed in pathological events.

Reinduction of T-Type Calcium Channels by Endothelin-1 in Failing Hearts In Vivo and in Adult Rat Ventricular Myocytes In Vitro

“…increased in atrial myocytes isolated from adult rats with growth hormone-secreting tumors, and Fares et al 8 reported that I Ca,T was observed in dedifferentiated adult ventricular myocytes cultured for 8 days with serum-containing media. Consistent with our previous reports, 12,13 in DS rats at the LVH stage, the LV tissue ET-1 peptide level was within normal limits, contrasting with the abrupt and massive increase at the CHF stage.…”

“…14 Adult ventricular myocytes were isolated from 11-to 13-week-old male Sprague-Dawley rats (nϭ7), purified (Ͼ98%), and primarycultured in laminin-coated dishes, following the protocol used by Piper et al 15,16 and Fares et al 8 …”

“…Interestingly, recent studies indicate that I Ca,T also reappears in myocardium with left ventricular (LV) hypertrophy or cardiac failure and under certain neurohumoral stimulations. [5][6][7][8][9] In these states, this transient channel may induce Ca 2ϩ overload, trigger-type arrhythmias, and Ca 2ϩ -dependent signaling that mediates cell apoptosis. Thus, inhibitors specific for this type of Ca 2ϩ channel may have clinical efficacy for preventing sudden death and progressive cardiac dysfunction in patients with diseased myocardium, although it has not yet been demonstrated.…”

HCN2 Overexpression in Newborn and Adult Ventricular Myocytes

“…Because a previous report indicated that longer culture conditions resulted in a marked positive shift in activation of native current, 9 we first compared native I f between acutely dissociated cells and cells maintained in serum-free medium for 2 days. All cells studied were rod-shaped and quiescent.…”

“…However, I f is present in both automatic 1 and nonautomatic [2][3][4][5][6] regions of the heart, and the threshold voltage varies widely among cardiac regions, being least negative in sinus node (Ϫ40 mV in rabbit 7 ) and most negative in ventricle (Ϫ108 mV or more negative 5,8,9 ). Interestingly, I f activates at less negative voltages in newborn ventricle (Ϫ70 mV in rat 8,10 ).…”