Abstract

The main goal of the study was to analyze the relationship between the signaling pathways regulating acetylcholine (ACh) quantal release in the peripheral synapse that are triggered by the activation of vanilloid (TRPV1) and purine receptors. In electrophysiological experiments carried out on the neuromuscular synapse of the mouse levator auris longus muscle, it was found that the frequency of miniature end-plate potentials (mEPPs) and the quantal content of end-plate potentials (EPPs) decrease in the presence of the TRPV1 receptor agonist capsaicin. This effect was completely reversed by SB 366791, a specific competitive TRPV1 receptor antagonist. ATP, like capsaicin, decreased the frequency of mEPPs and the EPP quantal content. In the presence of SB 366791, the inhibitory effect of ATP on ACh secretion realized its full. At the same time, in the presence of TRPV1 channel activation by capsaicin, the effect of ATP on both spontaneous and evoked ACh release was absent. It was suggested that the action mechanisms of ATP and capsaicin are underpinned by a change in Ca²⁺ entry into the nerve ending. To test this hypothesis, experiments were carried out to assess the changes in the presynaptic calcium level (Ca²⁺ transient) using a fluorescent calcium dye upon nerve stimulation. The amplitude of the Ca²⁺ transient did not change by either ATP application or capsaicin addition. Thus, in the neuromuscular synapse of mammals, along with the purinergic pathway of ACh secretion regulation, there is also a mechanism of neurosecretion modulation mediated by the activation of TRPV1 channels. The triggering of these mechanisms leads to the suppression of the processes of both spontaneous and evoked ACh quantal release from the motor nerve endings. It was demonstrated that both regulatory pathways are not accompanied by a change in the Ca²⁺ transient, but share a common link in ACh quantal release regulation.