In Situ Electrochemistry of Ru(NH₃)³⁺₆ in a Perfused Rat Heart

Simple two-electrode potential sweep and potential step electrochemical measurements are reported in a perfused living rat heart prepared using a modified in situ Langendorff preparation. Cyclic voltammetry of Ru(NH₃)³⁺₆ at Pt electrodes is performed in vivo after retrograde aortic perfusion of Ca²⁺- and albumin-free, oxygenated Krebs buffer containing Ru(NH₃)³⁺₆ to assess uniformity of perfusion. Four types of voltammetric response are observed depending on the placement of the working electrode. These types are distinguished on the basis of the relative contributions of diffusive and hydrodynamic mass transport as manifest in the shapes of the current-potential curves. Chronoamperometric measurement of double layer charging was used to estimate extracellular tissue resistance. These chronoamperometric experiments are performed in buffer solutions by small potential steps around a set potential of non-Faradaic activity. Tissue resistance was estimated to be ca. 598 ± 138Ω from the chronoamperometric data. The electrochemical responses observed from both measurements exhibit good reproducibility between individual heart preparations.