TRIS BUFFER - NEW METHOD FOR STUDYING PULSUS ALTERNANS IN ISOLATED HEART-MUSCLE

A regular alternation of strong and weak heart beats, i.e. pulsus alternans, could be induced in isolated heart muscle of guinea pigs or cats when the commonly used buffering agent Tris (hydroxymethyl) aminomethane was used instead of bicarbonate. Alternans developed spontaneously in Tris-buffered atria of guinea pigs when the Ca2+ concentration of the bathing medium was decreased from 2.5 to 1.0 mm, or when the Mn2+ concentration was increased from 0 to 0.5 mm; alternans persisted in Tris-bathed atria when stimulation frequency was changed from 1.0 Hz to 0.4, 0.8 and 1.6 Hz. Alternation of contractions similarly occurred in Tris-buffered ventricular papillary muscles of cats, especially when these preparations were challenged with even a temporary (1 to 2 min) increase in stimulation frequency. Alternans was not produced in bicarbonate-buffered heart muscle with the inotropic interventions studied. Present findings identify a previously unrecognized aspect of the cardiac effects of substituting Tris buffer for bicarbonate, and provide a model for studying the important cardiac phenomenon of pulsus alternans in heart muscle isolated from in vivo influences. © 1979.