The Role of the C-terminal IntracellularDomain in Acid-Sensing Ion Channel 3 Functioning

An increase in the concentration of protons in the synaptic cleft during neurotransmitters release is considered as one of the possible ways for postsynaptic membrane sensitization. The main sensors of acidification are acid-sensing ion channels (ASICs). The ASIC3 localized on the membrane of a sensing neuron contributes greatly to the perception of pain and is considered as one of the promising targets for the development of novel therapeutic agents. Despite a high degree of homology between mammalian ASIC3 channels, there is a number of differences among their orthologs. The major difference between human and rat ASIC3 is that, at physiological pH 7.4, the human ASIC3 responds to a fast acidic stimulus with practically a solitary sustained transmembrane current, while its rat ortholog generates a transient current with far higher amplitude, which precedes the sustained current. In this study, we demonstrate that the C-terminal intracellular domain (CTD) has a regulatory function, and its modification significantly affects transient current generation in human and rat ASIC3. A shortening of the CTD by 20 amino acid residues leads to a dramatic increase in the transient current and attenuation of the sustained current, while CTD modification in hASIC3 leads to the generation of a well-defined transient current like rASIC3, as demonstrated in whole-cell experiments on heterologically expressed channels. Furthermore, the deletion of 20 amino acid residues in the CTD increases the current amplitude by an order of magnitude both in rASIC3 and hASIC3. The obtained results demonstrate a prominent role of CTD in the intracellular regulation of ASIC3 channels.