Uterine smooth muscle tissue is a complex network of smooth muscle cells (SMC), interstitial cells of Cajal (ICC) and a nerve plexus (NP). In rat uterus a spontaneous activity of 1-2 contraction cycles per minute is regularly observed. Stimulation with oxytocin increases the amplitude and frequency of the contractions. In order to get more information about the properties of the three cellular components and their functions, a partial functional uncoupling of the three cell types was performed. Functional uncoupling of ICCs from SMC was performed using aThermalUncouplingProcedure (TUP). Functional uncoupling of NP from ICCs and SMC was performed using TTX 100 nM. Activation of SMC, ICC and NP was maintained using graded parameters for electrical field stimulation.

Under normal conditions uterine preparations showed cyclic contractions which could be also evoked by a EFS (1ms; 100 mA). Under this condition, NP was also activated, indicated by an increased tone. During TTX (0.1 mM) ICCs were still active but frequency was reduced (50%). The amplitude of the contractions was slightly reduced. EFS under this condition only activated the ICCs. TUP inhibited the activity of the ICCs and spontaneous smooth muscle contractions. EFS induced a tetanic tone of the SMC during activation of the NP. Further treatment with TTX under this condition induced again a titanic tone but of smaller amplitude.

Conclusion: Uterine SMCs do not show any rhythmicity in their contraction profile. Without the oscillatory pacemaker potential of the ICCs, this smooth muscle behaves like a time-invariant contracting tonic smooth muscle (for example: gastric fundus) (master-slave behaviour). The nerve plexus alone is also not able to activate the SMC in its normal manner but it can elicit activity when cyclically excited. Only in a functional combination with the ICCs, the nerval activity is able to modulate the uterine activity properly.