Besides being activated by G-proteinb⁄c subunits, G-protein activated potassium channels (GIRKs) are regulated by cAMP-dependent protein kinase. Back-phosphorylation experiments have revealed that the GIRK1 subunit is phosphorylatedin vivo upon protein kinase A activation inXeno-pusoocytes, whereas phosphorylation was eliminated when protein kinase A was blocked.