Wednesday, February 17, 2010

Extraglomerular Mesangial Cells

Extraglomerular mesangial cells are light-staining cells which are located outside the glomerulus, in the kidney, between the macula densa and the afferent arteriole. Also called Lacis cells, they form the juxtaglomerular apparatus in combination with two other types of cells: the macula densa of the distal convoluted tubule and Juxtaglomerular cells of the afferent arteriole. This apparatus controls blood pressure through the Renin-Angiotensin-Aldosterone system. The specific function of Lacis cells is not well understood, but it is believed that it is associated with the secretion of erythropoietin.

It has been hypothesized that fluctuations of the ionic composition in the interstitium of juxtaglomerular apparatus (JGA) modulate the function of extraglomerular mesangial cells (MC), thereby participating in tubuloglomerular feedback (TGF) signal transmission. Scientists have examined the effects of isosmotic reductions in ambient sodium concentration ([Na+]) and [Cl-] on cytosolic calcium concentration ([Ca2+]i) in cultured rat MC. Rapid reduction of [Na+] or [Cl-] in the bath induced a concentration-dependent rise in [Ca2+]i. MC are much more sensitive to decreases in ambient [Cl-] than to [Na+]; a decrease in [Cl-] as small as 14 mM was sufficient to elicit a detectable [Ca2]i response. These observations suggest that MC can be readily stimulated by modest perturbations of extracellular [Cl-]. Next, we examined whether activation of MC by lowered ambient [Cl-] influences cellular nitric oxide (NO) production.