Hydrogen sulfide's involvement in modulating nociception.

Hydrogen sulfide (H2S) is a malodorous gas which functions as an endogenous gasotransmitter in humans. It is becoming appreciated that H2S may be involved in a wide variety of processes including nociceptive processes. The molecular mechanisms responsible for many of the activities of H2S remain uncertain, however, H2S increases cAMP levels in neuronal and glial cell lines and primary neuron cultures with hyperpolarization. H2S may be involved in multiple signaling pathways and produce various effects on ion channels (e.g. T-type calcium channel currents, ATP-sensitive K+ (KATP) channels) which may inhibit or promote nociception. It is also conceivable that H2S may affect the n-methyl-d aspartate (NMDA) receptor complex and/or TRPA1 ion channels which may modulate nociceptive processes. It appears that H2S may regulate key neuronal functions, including the induction of hippocampal long-term potentiation, a synaptic model of learning and memory thought to involve the NMDA receptor as well as the release of corticotrophin-releasing hormone from the hypothalamus. It seems that the primary role of H2S in nociceptive processes is the activation of T-type calcium channels leading to facilitation of pronociceptive processes. A secondary contribution to the facilitation of pronociceptive processes may come from H2S-induced activation. It would appear that much like other gasotransmitters (e.g. nitric oxide), endogenous H2S may be involved in multiple physiologic processes and its effects remain complex, difficult to predict, and may vary depending on the specific environment/circumstances/location where it is generated. A greater understanding of the clinically significant human physiology of H2S and hydrogen sulfide's effects on modulating nociceptive processes may potentially lead to novel targets for improving analgesia.