Taurine depresses cardiac contractility and enhances systemic heart glucose utilization in the cuttlefish, Sepia officinalis
Taurine is the most abundant amino acid in the blood of the cuttlefish, Sepia officinalis, where levels can exceed 200 mmol L−1. In mammals, intracellular taurine modulates cardiac Ca2+ handling and carbohydrate metabolism at much lower concentrations but it is not clear if it exerts similar actions in cephalopods. Blood Ca2+ levels are high in cephalopods and we hypothesized that taurine would depress cardiac Ca2+ flux and modulate contractility in systemic and branchial hearts of cuttlefish. Heart performance was assessed with an in situ perfused systemic heart preparation and contractility was evaluated using isometrically contracting systemic and branchial heart muscle rings. Stroke volume, cardiac output, and Ca2+ sensitivity were significantly lower in systemic hearts perfused with supplemental taurine (100 mmol L−1) than in controls. In muscle ring preparations, taurine impaired relaxation at high contraction frequencies, an effect abolished by supra-physiological Ca2+ levels. Taurine did not affect oxygen consumption in non-contracting systemic heart muscle, but extracellular glucose utilization was twice that of control preparations. Collectively, our results suggest that extracellular taurine depresses cardiac Ca2+ flux and potentiates glucose utilization in cuttlefish. Variations in taurine levels may represent an important mechanism for regulating cardiovascular function and metabolism in cephalopods.