Myogenic properties of brain and cardiac vessels and their relation to disease.

Intrinsic arterial myogenic function comprises the degree of constriction (myogenic tone), the arterial constriction to an increase in intraluminal pressure and vice versa (myogenic response), and forced dilation at high intraluminal pressure. Although the development of myogenic tone at 40-60 mmHg involves the influx of calcium (Ca(2+)) through voltage- dependent Ca(2+) channels and an elevation in arterial intracellular Ca(2+) (Ca(2+) i), myogenic responses between 60-140 mmHg involves predominantly Rho kinase (ROK)-mediated changes in Ca(2+) sensitivity. In the cerebral circulation an impaired myogenic response results in impaired cerebral autoregulation and susceptibility hypertension-induced cerebral haemorrhage. An impaired cerebral artery myogenic response, due to blunted ROK mediated changes in Ca(2+) sensitivity, may be a consequence of defective mechanotransduction of the intraluminal pressure stimulus; this may be a result of abnormalities in the extracellular matrix. In the coronary circulation distinctions between the mechanisms involved in the development of myogenic tone and the myogenic response have not been clearly defined. However, coronary artery myogenic tone is dependent on both Ca(2+) entry through voltage -dependent Ca(2+) channels and protein kinase C (PKC) activity. Impaired coronary myogenic tone has been observed in animal models of disease but the implications of these findings are currently uncertain.