Enables guanyl-nucleotide exchange factor activity. Involved in response to organic substance. Located in several cellular components, including axon terminus; neuronal cell body; and postsynaptic density. Is active in glutamatergic synapse. Is integral component of postsynaptic density membrane and integral component of presynaptic membrane. Colocalizes with sarcolemma. Biomarker of congestive heart failure. Orthologous to human CHRM4 (cholinergic receptor muscarinic 4). [provided by Alliance of Genome Resources, Apr 2022]