[Receptor mechanisms underlying the actions of substance P and related neuropeptides]

The excitability of peripheral and central neurons is regulated by two types of ion channels, voltage- and ligand-operated ones. Recent studies have revealed that the activities of these ion channels are under the control of a variety of classical neurotransmitters and neuropeptides. In particular, certain ion channels such as voltage-dependent Ca and K channels are reciprocally regulated by excitatory and inhibitory neurotransmitters, leading to the excitation and inhibition of nerve cells: for example, 1) the activation of voltage-dependent K channel is facilitated by somatostatin and inhibited by substance P, and 2) the opening of voltage-gated Ca channel is augmented by substance P and suppressed by somatostatin and certain opioid peptides. The ligand-gated ion channel, nicotinic acetylcholine receptor is also controlled by the actions of neuropeptides, substance P and calcitonin gene related peptide (CGRP). The regulation of ion channels with neuropeptides may contribute not only to the control of neuronal excitability but also to the plasticity of the nervous system.