Tauret

Abstract

Since the first description of taurine in 1827³⁵ the range of biological phenomena involving this substance has progressively expanded. Efforts have been made to create a unifying theory for the actions of taurine^{10, 11, 36}. It is believed that “A limited number of basic mechanisms of action may underlie this confusing plethora of biological effects”¹⁰. In this respect, the actions of taurine as an osmolyte, its conjugation with bile acids and lipids, and its interactions with Ca²⁺, phospholipids, and chemoreceptors are of definite interest. Final understanding of the role of taurine in any organ or tissue is related to the elucidation of the relative contribution of these or a few other basic mechanisms in its function. It is necessary to clarify which is the primary action among the multiple actions of taurine in a given organ or tissue. For example, in some marine species the action of taurine as an osmolyte²⁶ seems primary. In liver, probably more central is taurine conjugation with bile acids and lipids, while in the heart taurine-Ca²⁺ interactions seem primary^{3, 5, 29}, although taurine may also be an osmoregulator in this organ³⁴. To understand the role of taurine in the retina it seems best to consider each cell system separately. Large amounts of taurine (10–40 mM) are characteristic for the retina of all species tested, even for those which have low taurine content in other tissues^{17, 20, 37}. Among the richer layers, photoreceptors are most abundant in taurine, containing 50–80% of the taurine pool of the retina^{15, 20, 37}. High levels of taurine in photoreceptor cells are mainly supported by taurine transport, which is predominantly localized around the photoreceptor cell nuclei¹⁴. About a 50% drop of taurine levels in the retina can be obtained either by a taurine-deficient diet in animals with low liver capacity for taurine synthesis^{9, 12, 31, 33} or by treatment of rats (which can synthesize taurine) with the taurine transport antagonist guanidinoethane sulfonate (GES)^{13, 25}. Retinal depletion of taurine causes serious alterations in the structure. The most severe retinal damage appears in the regions of highest rhodopsin content^{9, 12, 13, 25, 31, 33}. Taurine deficiency causes a noticeable reduction of rhodopsin level in rat photoreceptors¹³ and causes a drop of amplitude of the a-and b-waves of the electroretinogram (ERG)^{13, 31}.