Electrophysiological and electropharmacological actions of taurine on cardiac cells

Abstract

Effects of taurine on the L-type Ca2+ channel in isolated guinea pig ventricular cardiomyocytes were examined at different Ca2+ concentrations, using a whole-cell and cell-attached voltage-clamp mode. When [Ca](i) was pCa 6, addition of 10 or 20 mM taurine to the bath solution reduced I(Ca). In contrast, when [Ca](i) was pCa 8, I(Ca) at +10 mV was enhanced. Taurine increased the time constants (τ(f) and τ(s)) of the inactivation phase of I(Ca) current at both pCa 8 and 6. In cell-attached voltage-clamp experiments, taurine (20 mM) decreased the open probability of unitary Ba2+ current at 5.4 mM [Ca](o), whereas taurine increased it at 0.9 mM [Ca](o). Taurine did not affect the channel conductance. In addition, taurine (20 mM) increased the time constants (τ(of) and τ(os)) of the open time, and decreased τ(cs) of the closed time at 0.9 mM [Ca](o). At 5.4 mM [Ca](o), the τ(os) of open was increased and τ(cs) decreased. τ(of) and τ(cf) were unaffected. These results indicate that taurine modulates the L-type Ca2+ channel opening dependent on [Ca](i) and [Ca](o), thereby resulting in regulation of the cell function to normalize [Ca](i) level. From our previous experiments, Figure 5 represents a summary for the actions of taurine on the ionic currents of cardiomyocytes.