Alteration of the sodium current in cat cardiac ventricular myocytes during
primary culture.
Schackow, T. Eric, Michael F. Sheets, Robert S. Decker, and Robert E. Ten
Eick.
Department of Molecular Pharmacology & Biological Chemistry, Department of
Medicine, Department of Cellular, Molecular, and Structural Biology and The
Feinberg Cardiovascular Institute, Northwestern University, Chicago, Illinois
60611
APStracts 2:0010C, 1995.
To determine the response of the cardiac sodium current (INa) in adult cardiac
ventricular myocytes to culture, single isolated ventricular myocytes
obtained from collagenase-perfused adult cat hearts were placed in primary
culture for up to two weeks either on a two-dimensional (2D) surface
(laminin-coated coverslips) which allowed the morphology of the myocytes to
change markedly or in a three-dimensional matrix (3D) of alginate in which
cell shape changed only minimally. Action potentials and Na currents were
recorded from groups of (a) freshly isolated myocytes serving as the control
(day 0), (b) cells maintained in 2D-culture for 9-14 days (2D, day 9-14), and
(c) cells cultured in alginate for 9-14 days (3D, day 9-14) using a
conventional whole-cell-patch technique. Maximal upstroke velocity (max) of
the action potential was reduced by approximately 50% in both 2D- and 3D
-cultured cells relative to controls. INa in both 2D- and 3D-cultured cells
was strikingly different from that obtained in control myocytes. The half
-maximal voltage (V 1/2) for the chord conductance (GNa)-voltage (V)
relationship was shifted approximately 15 mV negatively to that for controls
in both 2D- and 3D-cultured cells. The INa steady state availability curve
also shifted negatively relative to controls in both 2D- and 3D-cultured
myocytes, but the magnitude of this shift (approximately 16-20 mV) was
greater than that for the GNa-V curve. The V 1/2 for INa availability
continued to shift negatively with time during voltage clamp at similar rates
in both control and 2D-cultured cells indicating that the 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. The voltage
dependencies of both INa onset and the fast and slow time constants of INa
decay ([tau]f and [tau]s) were shifted 10-30 mV negatively relative to
controls in all long-term cultured cells. These data suggest that primary
culture can alter INa in cardiac myocytes and that the changes in INa during
culture are not necessarily related to concomitant changes in cell shape.
Received 9 November 1993; accepted in final form 27 September 1994
APS Manuscript Number C0574-3.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1994 The American Physiological Society.
Published in APStracts on 27 February 1995.