Abstract: The impulse activities of muscle spindles isolated from the rat soleus muscle were investigated under varying concentrations of external calcium. The experiments were divided into low calcium modified Ringer′s solution group and high calcium modified Ringer′s solution group, using air gap technique to record the spontaneous discharge activities of isolated muscle spindle. And then with administrations of the corresponding modified Ringer′s fluid, the changes of the spontaneous discharges and evoked discharges by Succinylcholine chloride were recorded. After administration of Modified Ringer′s solution with low calcium, the spontaneous discharges of single muscle spindle were significantly increased(P<0.01), the interval of spontaneous discharge was shortened(P<0.01). After administration of Succinylcholine chloride, evoked discharges were not significantly increased. After administration of Modified Ringer′s solution with high calcium, the spontaneous discharges of single muscle spindle were significantly decreased(P<0.01), the interval of spontaneous discharge was prolonged(P<0.05). After administration of Succinylcholine chloride, evoked discharges were not significantly increased. The extracellular fluid with a low concentration of calcium ions can increase the spontaneous discharges of single muscle spindle of rats′ soleus muscle, and the extracellular fluid containing high calcium concentration can inhibit the spontaneous discharges of single muscle spindle of rats′ soleus muscle.

Key words: Ca2+, single muscle spindle, spontaneous discharge, rats