Cardiac Actions of Taurine as a Modulator of the Ion Channels

Abstract

During ischemia, hypoxia and cardiac failure, the heart undergoes several adverse changes, including a reduction in taurine (2-aminoethanesulfonic acid)^9,10. Oral administration of taurine under these disease conditions would be expected to act like a mild cardiac glycoside. Taurine would exert improvement in the accumulation of [Na]_i and the loss of α-amino acids. Nonetheless, when intracellular taurine content is raised, there would be the benefit of increased Ca²⁺ release from the sarcoplasmic reticulum and increased Ca²⁺ sensitivity of the contractile proteins, as well as possible changes in the action potential associated with the actions of taurine on ion channels. In fact, intracellular application of taurine produces the opposite actions to extracellularly administration of the ammo acid.

From our previous experiments, the electrophysiological actions of taurine on cardiac muscle cells include the following^3,28: (a) Prolongation of action potential duration (APD) at high [Ca]_i and shortening of APD at low [Ca]_i. In multicellular preparations, however, taurine did not always prevent [Ca]_o-induced effects. (b) Stimulation of spontaneous activity at low intracellular and extracellular Ca²⁺ concentrations ([Ca]_i and [Ca]_o), and vice versa. (c) Inhibition of the L-type Ca²⁺ current (I_Ca(L)) at high [Ca]_i, and vice versa. (d) Enhancement of the T-type Ca²⁺ current (I_Ca(T)). (e) Inhibition of fast Na⁺ current (I_Na). (f) Enhancement of TTX-insensitive slow Na⁺ current. (g) Inhibition of delayed rectifier K⁺ current (I_Krec) at high [Ca]_i, and vice versa. (h) Enhancement of the transient outward current (I_to). (i) Inhibition of the ATP-sensitive K⁺ current (I_K(ATP)).

Since taurine acts on so many ion channels and transporters, it is clearly non-specific. Although it is very difficult to understand the diversity of taurine’s actions, it is possible that taurine can exert its potent cardioprotective actions under the conditions of low [Ca]_i, as well as Ca²⁺ overload. Thus, although taurine-induced modulation of ion channels located on the cardiac cell membrane is complex, the multiple effects may combine to yield useful therapeutic results.