Voltage clamp of the cardiac sodium current at 37 degrees C in physiologic solutions.
The cardiac sodium current was studied in guinea pig ventricular myocytes using the cell-attached patch voltage clamp at 37 degrees C in the presence of 145 mM external sodium concentration. When using large patch pipettes (access resistance, 1-2 M omega), the capacity current transient duration was typically 70 microseconds for voltage clamp steps up to 150 mV. At 37 degrees C the maximum inward sodium current peaked in approximately 200 microseconds after the onset of a clamp step and at this strong depolarization, less than 10% of the sodium current developed during the capacity transient. The sodium current developed smoothly and the descending limb of the current-voltage relationship usually spanned a range of 40 mV. Moreover, currents reduced by inactivation of sodium channels could be scaled to superimpose on the maximum current. Current tails elicited by deactivation followed a monoexponential time course that was very similar for currents of different sizes. Data obtained over a range of temperatures (15 degrees-35 degrees C) showed that the steady-state inactivation and conductance-voltage curves were shifted to more negative voltages at lower temperatures. These results demonstrate the feasibility of investigating the sodium current of mammalian cardiac cells at 37 degrees C in normal physiological solutions.
Murray
K T
KT
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Anno
T
T
Bennett
P B
PB
Hondeghem
L M
LM
D000818:Animals; D002478:Cells, Cultured; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D008564:Membrane Potentials; D015222:Sodium Channels / Q000502:physiology*; D013696:Temperature; D016276:Ventricular Function
D015222:Sodium Channels