Total Ca handling in canine mild Ca overload failing heart

We analyzed total Ca handling of the left ventricle (LV) in the mildly fail ing heart preparation induced by a temporary intracoronary Ca overloading i ntervention in eight excised and cross-circulated canine hearts. This Ca in tervention consisted of interruption of coronary blood perfusion by Ca-free oxygenated Tyrode perfusion for 10 min followed by high-Ca (16 mmol/l) oxy genated Tyrode perfusion for 5 min. This intervention decreased the LV cont ractility index, E-max (end-systolic maximum elastance), by 40% after resto ration of the blood cross-circulation. We expected a Ca overload or paradox failing heart resembling the postischemic stunned heart and being characte rized by an increased O-2 cost of E-max. However, LV O-2 consumption under mechanically unloading conditions decreased by 30% from control without inc reasing the O-2 cost Of E-max. To Obtain a mechanistic view of this failing heart, we investigated cardiac total Ca handling by our integrative analys is method. In this method, we obtained the internal Ca recirculation fracti on (RF) from the decay beat constant of the postextrasystolic potentiation following each sporadic spontaneous extrasystole in these failing LVs. We c ombined the RF with the decreased E-max and the unchanged O-2 cost of E-max in our recently developed formula of total Ca handling. We found that thes e failing LVs had a slightly but significantly increased RF accompanied by either a slightly increased futile Ca cycling or a slightly decreased Ca re activity of E-max, or both. Any of these three possible changes can account for the unchanged O-2 cost of E-max. This result indicates that the presen t mildly failing heart has not yet fallen into a typical Ca overload or par adox by the temporary Ca overloading intervention.