Taurine modulates ion influx through cardiac Ca2+ channels.

The effects of taurine on the inward Ca2+ current (ICa) were investigated by means of the whole-cell voltage-clamp technique in isolated single guinea pig ventricular myocytes. ICa were elicited by 200-ms test pulses from a conditioning holding potential of -45 mV to various test potentials at a rate of 0.5 Hz. Taurine (10-20 mM) had different effects on ICa, depending on the extracellular Ca2+ concentration [( Ca]o). A small stimulatory effect of taurine was found in low [Ca]o (0.8 mM), and a small inhibitory effect was found in high [Ca]o (3.6 mM). Taurine had no significant effect on ICa in normal [Ca]o (1.8 mM). Such dual effects on ICa may explain the various effects reported for taurine especially its dual inotropic actions on cardiac muscle depending upon [Ca]o. Thus, taurine acts in a manner to keep ICa relatively constant. Taurine increased the resting potential irrespective of [Ca]o, suggesting that, in addition, taurine increased K+ conductance and/or ion exchange systems such as the Na/Ca and Na/K exchange.