Physiological and experimental regulation of taurine content in the heart.

High concentrations of taurine are found in the heart and these are increased still further in congestive heart failure. It appears that taurine is largely derived by influx from the circulation, and this influx is stimulated by cyclic AMP, whereas influx of alpha-amino acids is unaffected. Influx occurs via a saturable transport system that has strict requirements for ligands. Other substances are transported by this system, including beta-alanine, hypotaurine, guanidoethyl sulfonate, and, to a lesser extent, guanidinopropionate; and these are competitive antagonists for taurine transport. Guanidinoethyl sulfonate, in vivo, markedly lowers taurine concentrations over the course of a few days in all tissues examined in the rat and mouse (but not in the guinea pig). The concentrations of other amino acids are unaffected. Guanidinoethyl sulfonate may prove to be a useful substance in the study of the biological role of taurine, in view of its ability to regulate taurine content in a number of species. Despite the numerous pharmacological actions of taurine, its physiological function in the heart remains problematic. One function appears to be the modulation of calcium movements. The inotropic actions of taurine and beta-adrenergic activation may be linked via the cyclic AMP-dependent regulation of taurine influx.