Inotropic responsiveness of atrial myocardium bathed in Tris- or bicarbonate-buffered solutions.
Atrial muscle of guinea pigs was used to study the inotropic influences of substituting a tris(hydroxymethyl)-aminomethane-buffered solution aerated with 100% O2 for a bicarbonate-buffered solution aerated with 95% O2-5% CO2 under otherwise equivalent in vitro conditions. Basal values of isometric contractile tension and its first derivative (dT/dt) were smaller and time to peak tension and time to 90% relaxation were longer in Tris- than in bicarbonate-bathed muscles. Both groups responded similarly to changes in stimulation frequently (0.1--2.2 Hz) and Ca2+ concentration (1.0--7.0 mM); however, maximal inotropic responses to these variables were smaller in the Tris-bathed atria. The negative inotropic effects of D600 and gentamicin were greater in the Tris group. Tris-bathed atria developed pulsus alternans when exposed to Mn2+ or a reduced Ca2+ concentration, whereas pulsus alternans did not occur in the bicarbonate group. A transient increase in contractility occurred in bicarbonate-bathed atria after treatment with 0.125 mM Mn2+, but only a negative response occurred in the Tris group. Thus important, and seemingly Ca2+-dependent, differences exist between the inotropic influences of Tris and bicarbonate solutions that may affect the utility of Tris-buffered (and/or bicarbonate deprived) heart muscle for studying certain inotropic interventions.
D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D002021:Buffers / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005711:Gallopamil / Q000494:pharmacology; D005839:Gentamicins / Q000494:pharmacology; D006168:Guinea Pigs; D006325:Heart Atria; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*; D014325:Tromethamine / Q000494:pharmacology*
D001639:Bicarbonates; D002021:Buffers; D005839:Gentamicins; D014325:Tromethamine; D005711:Gallopamil; D002118:Calcium