Time course of force decline and recovery in rat soleus during 60 Hz direct stimulation in buffer or in air. Experimental conditions as described in the legend to Fig. 1, but muscles were exposed to direct stimulation via platinum wires in contact with the muscles. 0.2-ms pulses of 10 V were applied at a frequency of 60 Hz for 180 s, followed by 2 s trains of 0.2-ms pulses of 60 Hz at the indicated intervals. The muscles were either stimulated in K.R. buffer (filled symbols) or in air, after the buffer had been aspirated (open symbols). Each point represents the mean of observations on four muscles with bars denoting SEM. None of the differences between force recorded in buffer and in air reached statistical significance.