AJP - Cell Physiology, Vol 259, Issue 4 C599-C604, Copyright © 1990 by American Physiological Society
Different temperature sensitivity of cardiac Na+ channels in cell-attached and cell-free conditions
M. Kohlhardt
Physiological Institute, University of Freiburg, Federal Republic of Germany.
At 19 degrees C and after cooling to 9 degrees C, elementary Na+ currents
were recorded in cell-attached and inside-out patches from cultured
neonatal rat myocytes. The study aimed to define the temperature
sensitivity of single cardiac Na+ channels and to detect a possible
modulating influence arising from the recording conditions. Cooling
prolonged the open state by reducing the exit rate into a nonconducting
configuration [tau open; temperature coefficient (Q10) = 1.90 +/- 0.02] and
reduced the unitary current size (i(unit); Q10 = 1.26 +/- 0.03). Reopening
proved to be only slightly temperature dependent; the mean number of
sequential openings decreased to 91 +/- 2.1% of the value at 19 degrees C.
Cooled Na+ channels are still capable of switching to ultralong sequential
activity. Cooling reduced reconstructed peak Na+ current (INa) strongly,
with Q10 values between 1.85 and 3.11 (mean, 2.36 +/- 0.29), if Na+
channels remained in their natural environment as was the case in
cell-attached recording conditions. However, after disrupting the cellular
contact, in inside-out patches, the same 10 degrees C drop in temperature
diminished peak INa only slightly to 91 +/- 8.1% of the initial control
value at 19 degrees C. This suggests a modulating influence on the open
probability of cardiac Na+ channels arising from the cytosol of cooled
myocytes.
