A multitissue organ bath evaluated using new rabbit papillary muscle isolation methods

A multitissue organ bath was developed to study four isolated muscle preparations simultaneously under identical conditions. The multitissue bath was evaluated by determining the dose-response curves to dobutamine in isolated rabbit right ventricular papillary muscles. Several new procedures were developed to diminish the contracture shortening that often accompanies papillary muscle excision in this species. The excised heart was dissected in a hypothermic (22 degrees C) 'relaxing solution' containing 180 mM NaCl and 5.6 mM glucose, and a 'transfer clip' maintained constant, reproducible resting tension on the isolated muscle after its excision. Rabbit papillary muscles (n = 13) isolated with these procedures and studied in the multitissue bath were stimulated at a frequency of 20/min at 30 degrees C in a modified Krebs solution containing 2.5 mM Ca2+. Mean developed tension was 3.3 +/- 0.5 g/mm2. The dose-response curve for dobutamine demonstrated a maximal increase of dT/dt, an index of contractility, at 10(-4) M (173.6 +/- 35%, p less than 0.01). The multitissue bath may be useful for simultaneous comparison of chronotropic and inotropic effects of interventions on right atrial and ventricular preparations, respectively, or for comparison of intervention effects on selected vascular strips.