Latency relaxation in frog skeletal muscle under hypertonic conditions.

The effect of exposure to hypertonic conditions on latency relaxation (LR), twitch tension and resting tension in frog toe muscle was studied. Measurements were carried out in standard and hypertonic conditions (1 to 3.6 times standard tonicity) and following transversal stimulation. In hypertonic conditions, the LR showed increased duration and decreased amplitude. Both time course and amplitude showed the same dependency on sarcomere length as in standard conditions. The fall in amplitude and extension of the time course was proportional to the increase in tonicity up to 2.2 times the tonicity of the standard. At higher tonicities the time course extended earlier and diverged from the linear dependency, the amplitude falling later with increasing tonicity. The LR was abolished at tonicities exceeding 3 times the standard. In hypertonic conditions the twitch tension was reduced and extended, but showed the same dependency on sarcomere length as in standard conditions. The amplitude showed the same dependency on tonicity as the LR amplitude. The time course extended in a non-linear way with growing tonicity. In hypertonic conditions the resting tension was higher than or the same as in standard conditions, and the dependency on sarcomere length was the same.