Abstract
The relationship among contractile tension, ATP content and concentration was examined in isolated, superfused ventricular papillary muscle under normoxic (PO2=300 mmHg) and hypoxic (PO2=100 mmHg) conditions, using capillary isotachophoresis. The muscle preparations were exposed to each condition for 30 min, and the contractile tension was recorded with a strain gauge. Immediately after the recordings, the preparations were homogenized and the metabolites (ATP, ADP, AMP, creatine phosphate, inosine monophosphate, NAD, NADH, glucose-6-phosphate, pyruvate, and inorganic phosphate) were extracted in 50% methanol-1.25 mm EDTA solution at -20°C for 4 days. The supernatant of the extract was used for the isotachophoretic analysis. Hypoxia markedly depressed ATP content and concentration in the tissue. Under conditions of normoxia, but not hypoxia, the developed tension positively correlated with the ATP content and concentration. Under normoxic conditions, the tension tended to be proportional to the estimated surface area of the preparation, while in hypoxia it tended to be inversely proportional thereto. The ATP concentration appeared to be inversely proportional to the muscle weight, thereby suggesting that the outer layer of the preparation contains more ATP than the inner. In fact, an isotachophoretic analysis of the tissue revealed significantly higher ATP concentrations in the outer layer. Our findings indicate that there is a central anoxic core in the isolated canine papillary muscle superfused with oxygenated Tyrode solution and that surface layer ATP probably plays a pivotal role in the initiation of contraction.
