Electrophysiological analysis of colchicine-induced supersensitivity in the rat vas deferens.

1. The supersensitivity in smooth muscle of the rat vas deferens induced by local application of colchicine to the hypogastric plexus was investigated electrophysiologically. 2. Spontaneous junction potentials could be detected in nearly all of the impaled cells, but they occurred with lesser frequency and smaller amplitude in the colchicine-treated rat vas deferens than in the control tissue. However, this clearly demonstrated that, although attenuated, neuromuscular transmission still persisted after colchicine treatment. 3. The mean resting potential of smooth muscle cells of the colchicine-treated vas deferens (58.2 +/- 0.3 mV, n - 146) was not significantly different from that of the cells of the contralateral control tissue (58.1 +/- 0.2 mV, n = 130). 4. The threshold potential for action potentials induced by either nerve stimulation or extracellular current application was more negative by approximately 10 mV in the colchicine-treated vas deferens in comparison with the control tissue. 5. Externally applied current pulses of long duration failed to produce electrotonic potentials in any smooth muscle cell of normally innervated rat vas deferens which was located more than 0.5 mm from the partition electrode. In the colchicine-treated tissue, however, electrotonic potentials in the smooth muscle cell could be detected for a distance up to 2.5 mm from the partition electrode. The space constant in the colchicine-treated tissue was determined to be 0.79 +/- 0.02 mm (n = 10). 6. It is concluded that (i) the magnitude of depolarization from resting to threshold potentials in the colchicine-treated vas deferens was significantly smaller than that in the contralateral control tissue and (ii) that the current spread in a longitudinal direction was improved following colchicine treatment.