Taurine antagonizes the increase in intracellular calcium concentration induced by alpha-adrenergic stimulation in freshly isolated guinea-pig cardiomyocytes.
The effect of taurine on phenylephrine alpha-adrenergic action was studied in freshly-isolated guinea-pig ventricular myocytes. Intracellular calcium concentration was measured at nearly physiological extracellular CaCl2 in both cell suspension using quin-2 (mean intracellular calcium concentration 154.0 +/- 8.0 nM, n = 24), and single myocyte with fura-2 (mean intracellular calcium concentration 159.0 +/- 20.0 nM, n = 23). Phenylephrine increased intracellular calcium concentration in both preparations. In cell suspensions in the presence of 10(-6) M propranolol and at 2.2 mM extracellular calcium concentration, phenylephrine dose-dependently (3 x 10(-7)-10(-5) M) increased intracellular calcium concentration, its effect being abolished in the presence of phentolamine. Taurine 20 mM in the incubation fluid increased taurine content in the cells from 110 +/- 7 nmol/mg to 317 +/- 49 nmol/mg of total proteins. In the range 0.5-20 mM, taurine concentration-dependently reduced the phenylephrine-induced intracellular calcium increase in cell suspensions and 20 mM taurine decreased the effect of 10(-5) M phenylephrine (measured in the presence of 10(-6) M propranolol) by about 80%. Beta-Alanine (20 mM) did not modify the phenylephrine effect. Our data show that the "protective" effect of taurine in in vitro cardiac preparations and in cardiomyocyte isolation procedures is due to its effect on cardiomyocyte intracellular calcium ion concentration, and that taurine specifically antagonizes alpha-adrenoceptor activation.
Failli
P
P
Dipartimento di Farmacologia Preclinica e Clinica, Mario Aiazzi Mancini, Firenze, Italy.
Fazzini
A
A
Franconi
F
F
Stendardi
I
I
Giotti
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D016257:Fura-2; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D013654:Taurine / Q000494:pharmacology*
D013654:Taurine; D010656:Phenylephrine; D002118:Calcium; D016257:Fura-2