Unitary conductance of na+ channel isoforms in cardiac and nb2a
neuroblastoma cells .
Baumgarten, Clive M., Samuel C. Dudley, Jr, Richard B. Rogart, Harry
A. Fozzard.
Dept. of Physiology, Medical College of Virginia, Virginia
Commonwealth University, Richmond, VA 23298 and Depts. of Medicine
(Cardiology) and Physiological and Pharmacological Sciences, The
University of Chicago, Chicago, IL 60637
APStracts 2:0227C, 1995.
Unitary conductances (_Na) of native Na+ channel isoforms have been
determined under a variety of conditions making comparisons of _Na
difficult. To allow direct comparison, we measured _Na in cell
-attached patches on NB2a neuroblastoma cells and rabbit ventricular
myocytes under identical conditions (pipette solution: Na+ 280 mM,
Ca2+ 2 mM, pH 7.4; 10 degrees C). _Na of NB2a channels, 22.9 +/- 0.9
pS, was 21% greater than that of cardiac channels, 18.9 +/- 0.9 pS.
In contrast, extrapolated reversal potentials, +62.4 +/- 4.6 and
+57.9 +/- 5.1 mV, were not significantly different. Several kinetic
differences between the channel types also were noted. Negative to
-20 mV, mean open time (MOT) of the NB2a isoform was significantly
less than that of cardiac channels, and near threshold, latency to
channel opening decayed more rapidly in NB2a. Based on analysis of
MOT between -60 and 0 mV, the rate constants at 0 mV for the O C and
O I transitions were 0.42 +/- 0.11 and 0.47 +/- 0.11 ms-1 in NB2a and
0.10 +/- 0.06 and 1.19 +/- 0.07 ms-1 in myocytes. The slope factors
were -38.9 +/- 8.7 and +10.7 +/- 6.1 mV in NB2a and -27.3 +/- 7.1 and
+23.7 +/- 4.9 mV in myocytes. Transition rate constants were
significantly different in NB2a and cardiac cells, but voltage
-dependence was not.
Received 9 December 1994; accepted in final form 29 May 1995.
APS Manuscript Number C711-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.