ALTERATION OF THE SODIUM CURRENT IN CAT CARDIAC VENTRICULAR MYOCYTES DURING PRIMARY CULTURE

To determine the response of cardiac Na current (I-Na) in adult cardia c ventricular myocytes to culture, single isolated ventricular myocyte s from collagenase-perfused adult cat hearts were placed in primary cu lture for up to 2 wk on a two-dimensional (2D) surface (laminin-coated coverslips), which allowed the morphology of the myocytes to change m arkedly, or in a three-dimensional matrix (3D) of alginate, in which c ell. shape changed only minimally. Action potentials and I-Na were rec orded from groups of 1) freshly isolated myocytes serving as the contr ol (day 0), 2) cells maintained in 2D culture for 9-14 days (2D, day 9 -14), and 3) cells cultured in alginate for 9-14 days (3D, day 9-14) w ith use of a conventional whole cell patch technique. Maximal upstroke velocity (V-max) of the action potential was reduced by similar to 50 % in 2D- and 3D-cultured cells relative to controls. I-Na in 2D- and S D-cultured cells was strikingly different from that in control myocyte s. Half-maximal voltage (V-1/2) for the chord conductance-voltage rela tionship was shifted similar to 15 mV negatively to that for controls in 2D- and SD-cultured cells. I-Na steady-state availability curve als o shifted negatively relative to controls in 2D- and SD-cultured myocy tes, but the magnitude of this shift (similar to 16-20 mV) was greater than that for the chord conductance-voltage curve. V-1/2 for I-Na ava ilability continued to shift negatively with time during voltage clamp at similar rates in control and 2D-cultured cells, indicating that th e initial negative shift in V-1/2 in cultured cells was not caused by an acceleration of the previously described time-dependent shift in Na channel kinetics. Voltage dependencies of I-Na onset and fast and slo w time constants of I-Na decay were shifted 10-30 mV negatively relati ve to controls in all long-term cultured cells. These data suggest tha t primary culture can alter I-Na in cardiac myocytes and that changes in I-Na during culture are not necessarily related to concomitant chan ges in cell shape.