Properties of single cardiac Na channels at 35 degrees C

Single Na channel currents were recorded in cell-attached patches of mouse ventricular myocytes with an improved patch clamp technique. Using patch pipettes with a pore diameter in the range of 200 nm, seals with a resistance of up to 4 T omega were obtained. Under those conditions, total noise could be reduced to levels as low as 0.590 pA rms at 20 kHz band width. At this band width, properties of single-channel Na currents were studied at 35 degrees C. Six out of a total of 23 patches with teraohm seals contained channel activity and five of these patches contained one and only one active channel. Amplitude histograms excluding transition points showed heterogenous distributions of levels. In one patch, part of the openings was approximately Gaussian distributed at different potentials yielding a slope conductance of 27 pS. The respective peak open probability at -10 mV was 0.26. The mean open time was determined at voltages between -60 and -10 mV by evaluation of the distribution of the event-related gaps in the center of the baseline noise to be approximately 40 microseconds at -60 mV and 50-74 microseconds between -50 and -10 mV. It is concluded that single cardiac Na channels open at 35 degrees C frequently with multiple levels and with open times in the range of several tens of microseconds.