Differences in electrophysiological and contractile properties of mammalian cardiac tissues bathed in bicarbonate – and HEPES‐buffered solutions

Aim: The aim of this study was to compare the action potential configuration, contractility, intracellular Ca²⁺ and H⁺ concentrations in mammalian cardiac tissues bathed with Krebs and Tyrode solutions at 37 °C. Results: In Langendorff‐perfused guinea‐pig hearts, loaded with the fluorescent Ca²⁺‐indicator Fura‐2, or H⁺‐sensitive dye carboxy‐SNARF, shifts from Krebs to Tyrode solution caused intra‐cellular acidification, increased diastolic pressure and [Ca²⁺]_i, decreased systolic pressure and [Ca²⁺]_i, leading to a reduction in the amplitude of [Ca²⁺]_i transients and pulse pressure. Contractility was also depressed in canine ventricular trabeculae when transferred from Krebs to Tyrode solution. Shifts from Krebs to Tyrode solution increased the duration of action potentials in multicellular cardiac preparations excised from canine and rabbit hearts but not in isolated cardiomyocytes. All these changes in action potential morphology, contractility, [Ca²⁺]_i and [H⁺]_i were readily reversible by addition of 26 mmol L^?1 bicarbonate to Tyrode solution. Effects of dofetilide and CsCl, both blockers of the delayed rectifier K current, on action potential duration were compared in Krebs and Tyrode solutions. Dofetilide lengthened rabbit ventricular action potentials in a significantly greater extent in Tyrode than in Krebs solution. Exposure of canine Purkinje fibres to CsCl evoked early after depolarizations within 40 min in all preparations incubated with Tyrode solution, but not in those bathed with Krebs solution. Conclusion: It is concluded that the marked differences in action potential morphology, [Ca²⁺]_i, [H⁺]_i and contractility observed between preparations bathed with Krebs and Tyrode solutions are more likely attributable to differences in the intracellular buffering capacities of the two media.