Taurine inhibition of fast Na+ current in embryonic chick ventricular myocytes

Effects of taurine on the fast Na+ current (INa) in 17-day-old embryonic chick ventricular myocytes were examined using the whole-cell voltage-clamp technique. The cells were spherical (10-15 microns diameter) and had a capacitance of 9.8 +/- 1.3 pF. The experiments were performed at room temperature (22 degrees C), and the holding potential was -90 mV. After the patch membrane was broken, peak INa initially increased, and then decreased and became stable within 3-5 min. The experiments on taurine were started after INa had stabilized. The characteristics of INa were as expected, including sensitivity to tetrodotoxin (10 microM). When added to the bath, taurine inhibited INa and shifted the reversal potential in the hyperpolarizing direction. At 10 mM, taurine inhibited INa by 38.2 +/- 4.3%, and shifted the reversal potential by 10.2 +/- 3.1 mV. The time to peak current was slowed: 0.83 +/- 0.20 ms (n = 11) in control, 1.03 +/- 0.18 ms (n = 9) in 10 mM taurine, and 1.10 +/- 0.19 ms (n = 10) in 20 mM taurine. These effects of taurine were not reversed by 30 min washout. At low concentrations, taurine actually enhanced INa in 3 of 8 cells at 1 mM, and in 4 of 10 cells at 5 mM; the reversal potential was still shifted in the hyperpolarizing direction by 5.7 +/- 1.6 mV. The time course of inactivation (fitted as a single exponential at test potential of -30 mV) was not affected: 1.1 +/- 0.5 ms in control 1.2 +/- 0.4 ms at 10 mM taurine.(ABSTRACT TRUNCATED AT 250 WORDS)