Smooth Myocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 404

from the media to intima, secrete remodeling enzymes such as metallopeptidases,
and increase matrix protein synthesis, but decrease the production of contractile
proteins (smooth muscle -actin, smooth muscle myosin heavy chain, transgelin). 29 α

8.5.1 Vascular Smooth Myocyte Subtypes

Several subpopulations of smooth myocytes (length 20-60 m, center width

∼ m) can be described in the arteries, such as spindle-shaped smooth myocytes

(sSMC) and rhomboid SMCs (rSMC). The SMC morphology can be modulated by
growth factors and environmental stimuli [ 746 ]. A large proportion of rSMCs is
observed after stent implantation (Vol. 6 - Chap. 10. Treatments of Cardiovascular
Diseases), with high proliferative and migratory activities.

4

8.5.2 Mesangial and Juxtaglomerular Cells

In kidneys, mesangial cells are smooth muscle-like cells that participate in the
formation of glomeruli of nephron entries. The glomerulus filters blood supplied
by an afferent arteriole that drains into an efferent arteriole to yield urine into the
Bowman's capsule, the basic filtration unit of nephron. The blood-urine filtration
barrier is constituted by endothelial cells of the glomerulus, negatively charged
glomerular basement membrane (thickness 250-350 nm), and podocytes of the
Bowman's capsule that control the filtration of proteins. Glomerular mesangial cells
lodge in the interstitium between endothelial cells. They control the filtration surface
area and the local blood flow, as they can contract in response mainly to stretch.
They also secrete extracellular matrix constituents, prostaglandins, and cytokines.
They scavenge molecules entrapped in the glomerular basement membrane.
Specialized mural, granular smooth myocytes, the so-called juxtaglomerular
cells , reside in the wall of the afferent arteriole of each nephron. The juxtaglomeru-
lar apparatus localizes between the vascular pole of the renal corpuscle (initial
blood-filtering component of the nephron with the glomerulus and Bowman's
capsule) and the distal convoluted tubule of the nephron. Juxtaglomerular cells
synthesize, store, and secrete renin. Renin activates the angiotensin cascade to
regulate blood volume and pressure. Juxtaglomerular cells are endowed with 1-

adrenergic receptors. Once stimulated by cathecholamines, these receptors provoke
renin secretion.

β

29 Promoter of genes of differentiated SMC markers contain common cis elements, among them
multiple CC(A/T-rich)6GG (CArG) motifs and a TGF

β

control sequence.