May play an important role in cardiac antiarrhythmia via the strong suppression of voltage-gated L-type Ca(2+) currents. Regulates voltage-dependent L-type calcium channel subunit alpha-1C trafficking to the cell membrane (By similarity). Inhibits cardiac hypertrophy through the calmodulin-dependent kinase II (CaMKII) pathway. Inhibits phosphorylation and activation of CAMK2D. Interacts with calmodulin preferentially in the inactive, GDP-bound form. Binds CAMKII which is capable of phosphorylating RAD in vitro. Interacts with CAMK2D and CACNB2. Interaction with CACNB2 regulates the trafficking of CACNA1C to the cell membrane (By similarity). Most abundantly expressed in the heart. Also found in the skeletal muscle and lung. Lesser amounts in placenta and kidney. Also detected in adipose tissue. Overexpressed in muscle of type II diabetic humans. Down-regulated in failing hearts. Belongs to the small GTPase superfamily. RGK family.