The physiological significance of GRK4 at the tunica adventitia, however, remains to be determined because GRK4 in this layer does not participate in the Ang II–mediated vasoconstriction.21 In addition, we found that GRK4 is expressed in the myocardium, which is involved in the regulation of myocardial ischemia. The gene discussed is GRK4; the disease is myocardial ischemia.