Measurement of the Na background currents in small cells

The authors measured the steady state Na current using the whole cell voltage clamp method in 19 ventricular cells from neonatal rats. In 12 cells they found a complex I/V relationship that showed two peaks at -46.9/spl plusmn/1.9 mV and -19.1/spl plusmn/1.6 mV and the mean amplitude of both was -5.1/spl plusmn/1.0 pA, In five cells the existence of two peaks was uncertain and the two remaining cells showed only one peak. In the I/V relationship showing two peaks both peaks were abolished by 200 /spl mu/M TTX. The I/V curves could be fitted to a model consisting of two different Na channels exhibiting window currents resulting from an overlap of the voltage range of steady state activation and inactivation. The model is also compatible with one type of Na channel showing two different modes of operation.