Influence of the size of syncytial units on synaptic potentials in smooth muscle.

The effect of the size of syncytial bundles of cells on the passive synaptic potentials generated within them has been explored. Computer simulations have been performed of neuronally produced spontaneous excitatory junction potentials (SEJPs) generated in cubical 'bidomain' model of syncytial tissue. It is found that indical properties of SEJPs vary conspicuously in syncytium sizes smaller than about 15-17-cube, but change very little in syncytium sizes greater than this. At the centroid of the cube, the peak amplitude Vp of the SEJP declines from 14.32 mV to 11.70 mV as syncytium size increases from 7-cube to 15-cube, i.e. a decrease of approximately 18%, while between system sizes 15-cube (Vp = 11.70 mV) and 29-cube (Vp = 11.67 mV), the reduction is only approximately 0.3%. Similar trends are observed for the time to peak of SEJPs. These observations indicate a minimum bundle size in smooth muscle below which syncytial function is modified; the implications of this are discussed.