MESANGIAL MATRICES ACT AS MESANGIAL CHANNELS TO THE JUXTAGLOMERULAR ZONE - TRACER AND HIGH-RESOLUTION SCANNING ELECTRON-MICROSCOPIC STUDY

The mesangium is centrally located in the glomerulus and plays an impo rtant role in the microcirculation within the glomerulus. In order to reveal the role of the mesangial matrix in the microcirculation, the m ovement of native anionic ferritin into the juxtaglomerular region was tracked following the intravenous injection of ferritin into rats. Th e three-dimensional ultrastructures of the mesangial matrix and juxtag lomerular apparatus were studied by conventional scanning and high-res olution scanning electron microscopy after removal of the cellular com ponents. Many ferritin particles were observed from the glomerular cap illary to the mesangial matrix, in the mesangial matrix of the juxtagl omerular apparatus and in the tubular lumen of the macula densa after the injection of ferritin. Secretion of macromolecules from the distal tubules seems to be one of the exits from the juxtaglomerular zone. T he mesangial matrix was continous from the vascular pole to the periph ery like a branching tree. The intraglomerular mesangial matrix was co ntinuous to the extraglomerular mesangial matrix in the juxtaglomerula r region. The mesangial matrix appeared to consist of a polygonal mesh work structure of thin fibrils and pores with high-resolution scanning electron microscopy. The thinnest fiber was approximately 6-nm wide, and the pore size was averaged 20 nm in diameter. We were able to demo nstrate the meshwork structure of the mesangial matrix, thus giving th e morphological basis of the mesangial matrix to serve as mesangial pa thway from the intraglomerular to the extraglomerular mesangial matrix .