Ischemia in isolated interventricular septa: mechanical events

Abstract

Isolated blood-perfused rabbit interventricular septa were adapted for studies of global ischemia by enclosure in a constant-humidity N atmosphere. During ischemia, developed tension (DT) and maximal rate of relaxation (-dP/dt) declined monoexponentially, .lambda. = 0.39 min-1 at 37.degree. C and 72 beats/min with a Q10 of 1.4 for DT and a Q10 of 1.9 for -dP/dt. After a 60- to 90-s delay the maximal rate of tension development (+dP/dt) declined at the same rate as DT. Time-to-peak tension shortened immediately with ischemia but action potential duration shortened after 60-90 s. Ca at a concentration of 5 mM slowed the rate of decline of +dP/dt to .lambda. = 0.26 min-1. Upon reperfusion after 10 min of ischemia the rates of recovery of DT, +dP/dt, and -dP/dt were similar, .lambda. = 0.21-0.23 min-1, and were not temperature dependent. The magnitude of recovery was 10-17% less at 37.degree. C than 28.degree. C. K at a concentration of 10 mM did not alter the rate of decline of mechanical function, but significantly (P < 0.01) increased the magnitude of mechanical recovery. The results suggest depletion and/or repletion of single compartments as the rate-limiting steps in ischemia and reperfusion.