Inhibition by taurine of the inwardly rectifying K+ current in guinea pig ventricular cardiomyocytes

Effects of taurine on the inwardly rectifying K+ current (IK1) in isolated guinea pig ventricular cardiomyocytes were examined using patch voltage-clamp methods. All experiments were performed at 36 degrees C. Taurine (10-20 mM) increased the action potential duration, but failed to affect the resting potential. Holding potential was maintained at -30 mV. The current was activated with an inwardly going rectification, and was completely blocked by Ba2+ (2 mM). Taurine inhibited IK1 at - 120 mV by 28.3+/-1.1% (n=6, P < 0.05) at 10 mM and by 36.0+/-2.1% (n=6, P < 0.01) at 20 mM. The reversal potential was shifted in the hyperpolarizing direction by 3.7+/-0.6 mV (n=6) at 20 mM. In inside-out patch-clamp experiments, the amplitude of unitary channels was -2.7+/-0.3 pA (n=21) at -90 mV. Symmetrical high-K+ (150 mM) solutions in both bath and pipette were used. The channel conductance was 32+/-2 pS (n=9). Taurine did not affect channel conductance, but markedly decreased the open probability at - 120 mV of channel by 21.5+/-2.4% (n=8, P < 0.01) at 10 mM, and by 56.7+/-3.8% (n=8, P < 0.001) at 20 mM. These responses were almost reversible. These results suggest that taurine directly modulates the open probability of the inwardly rectifying K+ current, resulting in regulation of the functions of heart cells.