CONTRACTILITY OF THE RENAL GLOMERULUS AND MESANGIAL CELLS: LINGERING DOUBTS AND STRATEGIES FOR THE FUTURE.

Kidneys can be divided into four components: glomeruli, tubules, interstitium and blood vessels. The renal glomerulus consists of a network of capillaries covered with epithelial cells called podocytes. The entire glomerular tuft is structurally supported by mesangial cells which are contractile in nature and resemble vascular smooth muscle cells. Mesangial cells are secretory, producing growth factors and matrix proteins which have a role in both normal glomerular development and in pathologic states. They have also been shown to take the role of macrophages. The importance of mesangial cell contraction to glomerular physiology remains debated. It is postulated that mesangial cell contraction can attenuate the glomerular filtration rate by decreasing the renal ultrafiltration coefficient through a decrease in capillary surface area and capillary permeability. The physiology of mesangial cell contraction has been studied primarily utilizing cultured cells. The physiological status of receptors and ion channels may be doubtful, however, given the phenotypic changes cells are known to acquire in culture conditions. The contractility of renal glomeruli has been less well studied. In this report, we review the available data regarding the contractility of mesangial cell and of renal glomeruli. Moreover, we suggest newer techniques that can be used with whole glomeruli, thereby improving upon the data collected using previous techniques and cultured cells.