Methods for analyzing the gate-kinetics of cardiac Na^＋ channels

A quantitative description of the Na^＋ channel properties is essential in electropharmacological studies on the modes of action of local anesthtics and antiarrhythmics. The recent advance in techniques of isolating single cardiomyocytes and voltage-clamping the total membrane area of the whole-cell with single patch electrodes have provided a useful tool for Na^＋ current studies in heart tissues. We successfully recorded Na^＋ channel currents under the physiological conditions (140 mM [Na^＋]_0) nad analyzed the gating linetics of current flow according to hodgkin-Hucley model, so that the time course of Na^＋ current could be described with four voltage-dependent variables (m_∞, τ_m, h_∞ and τ_h) and two constants (<g_Na>^^^- and E_Na). In Na^＋ current studies use of embryonic chick heart clees was found to be advantageous because of better ”space-clamp” due to their spheroidal shapes and the small cell size.