Isoproterenol-stimulated taurine influx in the perfused rat heart

Myocardial failure in cats associated with low plasma taurine: a reversible cardiomyopathy

Thousands of pet cats die each year with dilated cardiomyopathy, the cause of which is unknown. Although taurine is present in millimolar concentrations in the myocardium of all mammals, taurine depletion has not previously been associated with a decrease in myocardial function in any species. In this study, low plasma taurine concentrations associated with echocardiographic evidence of myocardial failure were observed in 21 cats fed commercial cat foods and in 2 of 11 cats fed a purified diet containing marginally low concentrations of taurine for 4 years. Oral supplementation of taurine resulted in increased plasma taurine concentrations and was associated with normalization of left ventricular function in both groups of cats. Since myocardial concentrations of taurine are directly related to plasma concentrations and low plasma concentrations were found to be associated with myocardial failure in cats, a direct link between decreased taurine concentration in the myocardium and decreased myocardial mechanical function is proposed.

Protective effect of taurine against isoprenaline-induced myocardial damage

The effect of the sulfur amino acid, taurine, was examined on histological and biochemical changes induced by a toxic dose of isoprenaline in chick hearts. Isoprenaline treatment (80 or 240 mg/kg id twice daily for 4 days) caused a dose-dependent increase in heart weight and decrease in myocardial ATP. Isoprenaline administration (240 mg/kg id twice daily) produced necrotic changes in hearts, such as eosinophilic degeneration, myolysis, interstitial oedema, fibrosis, and inflammatory cell infiltration. Substantial accumulation of calcium was also observed. Taurine content of the heart was not significantly decreased. Parenteral administration of taurine (200 mg/day for 7 days) partially protected against these necrotic changes induced by isoprenaline. It is suggested that the protective effect of taurine against isoprenaline-induced myocardial injury might be due in part to the prevention of the massive overloading with calcium which is thought to cause myocardial cell necrosis.

Regulation of taurine transport in rat skeletal muscle

Taurine concentration of soleus muscle (SL, slow-twitch) was initially about twofold higher than that of extensor digitorum longus muscle (EDL, fast-twitch). Taurine concentration in gastrocnemius muscle (GC) was intermediate between that of EDL and SL. Four days after sciatic nerve section, taurine concentration in the EDL but not in the SL was increased by 2.5-fold. The increase was not due to the muscle atrophy and was observed 28 days after denervation. Tenotomy did not increase the total taurine content of the EDL. The increase in taurine concentration of the denervated EDL was prevented by simultaneous ingestion of guanidinoethane sulfonate, a competitive inhibitor of taurine transport. The initial and the maximal rates of [3H]taurine uptake were significantly higher in SL than in EDL. Denervation dramatically accelerated the initial and the maximal rates of the transport in EDL, whereas it significantly reduced those in SL. In contrast, the electrical stimulation of sciatic nerve accelerated the uptake of taurine by EDL and SL of the control but not of the curare-treated rats. These results suggest that transport of taurine into rat skeletal muscles is regulated differently by neural information and by muscular activity, and that the regulation is dependent on the muscle phenotype.

Effects of taurine and verapamil on heart calcium in hamsters and rats

Heart calcium was measured in hamsters and rats following 30 days of drinking (i) tap water, (ii) taurine solution (T) or (iii) a taurine uptake inhibitor (GES). The regimes were duplicated in animals receiving verapamil (V). Heart calcium was reduced in both species by T + V; a comparable effect was obtained with GES alone; T alone had no effect. In the hamster, the GES effect was reversed by GES + V; V alone had no effect. In rats, the separate and combined effects of GES and V on heart calcium were identical. Possible mechanisms and underlying species differences are discussed.

Comparison of taurine-verapamil interaction in hamsters and rats

Taurine concentrations were determined in hearts and whole blood of female Syrian golden hamsters and Wistar rats following 30 days of drinking: (i) tap water, (ii) taurine solution or (iii) a taurine uptake inhibitor (GES). The groups were duplicated in animals receiving daily verapamil injections during the treatment period. Heart taurine increased with (ii) and decreased with (iii) in both species; blood taurine changed similarly in rats only. Verapamil enhanced taurine uptake and offset the GES inhibition in the hamster heart, but had no such effect in rats. Possible implications of the species differences are elaborated upon.

The beta-amino acid transport system in Friedreich's ataxia

Taurine and beta-alanine uptake in cultured skin fibroblasts proceeds through at least two distinct amino acid transport systems. The predominant beta amino acid uptake system which we refer to as the "Beta" system, incorporates taurine in a proportion of 95%. Beta-alanine in a proportion of 80% and does not incorporate beta-amino-isobutyric acid. A second transport system for beta-alanine seems to be operative cultured skin fibroblasts and this system shares the characteristics of system "L" for branched-chain and ring-side neutral amino acids. Results of ion depletion experiments, metabolic inhibition by drugs and blocking agents and previous kinetic studies of taurine and beta-alanine uptake in cultured skin fibroblasts failed to disclose any major difference in beta-amino acid transport between control individuals and patients with Friedreich's ataxia.

Pharmacokinetic studies of taurine in bovine Purkinje fibers

Taurine (2-aminoethane sulfonic acid) is found in high concentrations in the heart, particularly in Purkinje fibers. We studied the transport of taurine in Purkinje fibers that were excised rapidly from the heart and placed in a vessel containing oxygenated Krebs-Henseleit solution (37 degrees C). After equilibration, 4.4 x 10(-6)M radiolabeled taurine[14C] was added to the bath. A computer compartmental analysis of the uptake and efflux indicated the presence of two pools for uptake--a pool with a rapid kinetics K1 (t1/2 = 0.80 min) and K2 (t1/2 = 176.30 min). These studies suggest that Purkinje fibers have the capacity to transport taurine rapidly. Michaelis-Menten procedures showed the presence of a high affinity and a low affinity transport process. Guanidinotaurine, at a 10:1 ratio, had no appreciable effect on taurine uptake, but 3-aminopropane phosphonic acid decreased taurine uptake by 42.7%. Ouabain and acetylstrophanthidin (10(-5) M) inhibited taurine uptake (K1) by 34% and 73%, respectively. The inhibition of the rapid component of taurine uptake suggests that K1 is an energy-linked process possibly requiring Na+,K+-ATPase. Taurine uptake in a calcium-free medium was decreased by 58%. Verapamil (6 x 10(-6) M) decreased taurine uptake by 42%. Tetrodotoxin (3.4 x 10(-5) M) decreased taurine uptake by 51%. The requirement of calcium and sodium for taurine uptake suggests an important relationship between taurine, calcium, and sodium in the function of fibers in the cardiac conducting system.

Differential effects of amrinone on contractility and taurine influx in rat and guinea pig hearts

Amrinone (5-amino-3,4'-bipyridin-6(IH)-one) is a non-glycoside, non-catecholamine, positive inotropic agent with an unknown mechanism of action. In the Langendorff-perfused isolated guinea pig heart, we found that amrinone produced a maximum increase in contractile force of 33% at a concentration of 10 micrograms/ml (10.7 x 10(-5) M), without change in heart rate. Maximum response occurred within 2 min of initiating perfusion, and increased contractility persisted for several minutes of drug-free washout. Amrinone neither alleviated nor aggravated spontaneous arrhythmias. At the time of maximum inotropic response, amrinone produced no change in cyclic AMP levels. In contrast to the guinea pig, the Langendorff-perfused isolated rat heart responded with a decreased contractility when perfused with amrinone. Furthermore, whereas amrinone stimulated the influx of taurine in guinea pig hearts, taurine influx remained unaltered in rat hearts. This is the first case of stimulated taurine influx not being associated with an increase in cAMP concentrations. In the guinea pig heart, amrinone increased markedly the half life of exchange of intracellular calcium. It has been suggested that amrinone is positively inotropic because of a direct action on the contractile proteins. On the basis of our observations, we think it more likely to be due to the alterations in calcium flux caused by amrinone.

The mechanism of the adrenergic stimulation of taurine influx in the heart

The mechanism of isoproterenol-stimulated taurine uptake was examined in the perfused rat heart. Hearts were perfused by the Langendorff technique in a non-recirculating system, while heart rate and contractile force were determined continuously. Perfusion with inotropic concentrations of glucagon stimulated the uptake of [3H]taurine. If the positive inotropic response to isoproterenol was blocked with verapamil, a calcium antagonist, the uptake of taurine was still stimulated. This indicates that inotropy per se, or calcium influx are not involved in the modulation of taurine influx, but that influx rats is responding to cell cyclic AMP levels. The lack of effect of the positively inotropic ionophores monensin and A23187 and the negatively inotropic ionophore valinomycin is in agreement with this conclusion. Taurine decreased calcium binding to cardiac sarcolemma by 31% at 1 mM concentration and 80% at 5 mM.