Rat diaphragm muscle contraction with and without oxygen enrichment.

We investigated the effect of deprivation of oxygen circulation in the organ bath on the tension generation of the diaphragm in vitro. Adult male Swiss Albino rats were quickly killed and the left hemidiaphragms removed. Isolated phrenic nerve-diaphragmatic strip preparations were placed in an individual organ chamber containing Krebs solution and were connected to a force displacement transducer. The solution was maintained at 32 degrees C and bubbled with 95% O2-5% CO2. For the measurement of isometric twitch characteristics, supramaximal voltage was delivered via phrenic nerve electrodes. After turning off the gas circulation, isometric twitch characteristics were determined at 5, 10, 15, and 20 minutes. Then the muscle was allowed to recover under aerobic conditions (i.e., while bathed in a fresh solution, gassed with 95% O2-5% CO2). The isometric contractile properties were determined at the same intervals. In spite of no change in contraction time (CT) and relaxation time (1/2 RT), twitch amplitude (Pt) decreased following the termination of oxygen circulation (p < 0.05). The twitch tension improved in the recovery period but the decrease of tension developed more rapidly than the increase of tension development. We suggest that the decrease in the twitch tension was possibly due to a direct effect of intracellular acidosis. This study shows that no important change occurred in Ca+2 release and/or in the uptake in the sarcoplasmic reticulum, because of the finding of the CT and 1/2 RT values.