What is the fine-grained topic of the following text: Alternative splicing of four ASIC-encoding genes leads to the expression of six subunits (ASIC1a, ASIC1b, ASIC2a, ASIC2b, ASIC3,and ASIC4) that combine to form hetero- or homotrimericchannels that differ in their pH sensitivity, kinetics, and susceptibility to desensitisation. Only return the topic.
Alternative splicing of ASIC-encoding genes and resulting subunits