Temperature and inhibitory junctional transmission in guinea-pig ileum

The effects of temperature on the inhibitory junctional potential (i.j.p.) and the electrotonic potential, recorded in the circular smooth muscle of the guinea-pig ileum, were studied with intracellular microelectrodes. The amplitude and time course of the i.j.p. were both dependent on the ambient temperature, the i.j.p. becoming smaller and more prolonged as the temperature was lowered. In contrast, the electrotonic potential was not much affected by temperature. The atropine-resistant 'late' depolarization was also dependent on temperature. These results are consistent with the mechanism of release, of the nonadrenergic noncholinergic inhibitory transmitter, being sensitive to temperature and with the inhibitory conductance change, underlying the i.j.p., being long compared to the membrane time constant of the circular smooth muscle.