Plasma membrane and its abnormalities in hypertension

The plasma membrane is composed of proteins embedded in a discontinuous fashion in a lipid bilayer. These proteins maintain the integrity of the membrane and play fundamental roles as ion transport channels and as receptors for agents that regulate cell function. The membrane is therefore an important regulator of vascular smooth muscle contraction. The plasma membrane in the hypertensive animal exhibits abnormal permeability for monovalent ions and defective calcium handling. This is reflected in fewer calcium-binding sites and, as a result, in deficient membrane stabilization. These defects have been identified in several cell types, including lymphocytes, red blood cells, adipocytes, and vascular smooth muscle cells. Evidence presented in the current review suggests that hypertension is associated with a generalized membrane defect. Abnormalities in ion transport in vascular smooth muscle cells are the most relevant to the pathogenesis of hypertension since they could be directly responsible for the rise in blood pressure. We hypothesize that the impaired stabilizing effect of calcium in vascular smooth muscle cells of hypertensive subjects renders the membrane more excitable and that this in turn leads to increased vascular reactivity and higher peripheral resistance. Peripheral vascular reactivity usually is increased in hypertension, suggesting increased responsiveness of the smooth muscle cells. Possible abnormalities of the several components of the contractile process of these cells have been investigated for the role they might play in this altered response. Abnormalities in the plasma membrane have been most clearly defined and are emphasized in this review.