Identification of the Components of Excitatory Junction Potentials in the Guinea Pig Vas Deferens

Abstract

The contributions to the generation of excitatory junction potentials (EJPs) during neurotransmission in a smooth muscle organ have been investigated. The effects of nerve stimulation intensity on EJPs with complex time courses have been explored in the guinea pig vas deferens. It is shown that complex EJPs are resolvable into intermediate rapid and slow components, produced by the activity of separately recruitable innervating axons. The effects of the putative gap junctional uncoupling agent heptanol on EJPs have also been studied. Heptanol abolished the EJP reversibly. However, brief stimulus-locked depolarizations continued to occur intermittently at the same latency as the EJP even while the EJP was completely suppressed. These depolarizations had properties very similar to those of SEJPs, and reflect the fundamental quantal depolarizations underlying the EJP. They are termed quantal EJPs (QEJPs). Our results show that there are two principal contributions to the generation of the EJP, namely (i) QEJPs produced by the activity of individual varicosities; (ii) the intermediate components produced by the recruitment of axons and simultaneous activation of several varicosities. These events sum together to generate the EJP of the vas deferens.

Key Words:

• Junction potentials
• Smooth muscle
• Neurotransmission