Regulates G protein-coupled receptor signaling cascades, including signaling downstream of the muscarinic acetylcholine receptor CHRM2. Inhibits signal transduction by increasing the GTPase activity of G protein alpha subunits, thereby driving them into their inactive GDP-bound form (PubMed:10608901, PubMed:11443111, PubMed:18434541, PubMed:8774883, PubMed:9353196). Modulates the activity of potassium channels that are activated in response to CHRM2 signaling (PubMed:11443111). Activity on GNAZ is inhibited by palmitoylation of the G protein (PubMed:9353196). {ECO:0000269|PubMed:10608901, ECO:0000269|PubMed:11443111, ECO:0000269|PubMed:18434541, ECO:0000269|PubMed:8774883, ECO:0000269|PubMed:9353196}. This is the function of RGS10 (regulator of G protein signaling 10, Ensembl gene identifier ENSG00000148908).