Noradrenaline as a possible mediator of angiotensin II induced fluid transport in rat ileum in vitro

In isolated segments of ileum excised from bilaterally adrenalectomized and nephrectomized rats, 10(-12) M angiotensin or 10(-3) M noradrenaline added to serosal medium stimulated both fluid transfer and NaCl transport. The alpha adrenergic antagonist phentolamine blocked the stimulation of fluid transfer induced by angiotensin. These results are consistent with the hypothesis that noradrenaline may mediate the increase of intestinal fluid absorption induced by angiotensin in the rat. In segments of isolated ileum from normal rats 10(-12) M angiotensin only stimulated fluid transfer under one of the two following conditions when 10(-3) M imipramine, a noradrenaline uptake blocker, was present in the serosal medium; or when the rats had been previously treated with L-Dopa, a precursor of noradrenaline biosynthesis. These results suggested that the necessity for bilateral adrenalectomy and nephrectomy might be associated to the necessity of increasing the tissue levels of noradrenaline. Direct measurement of noradrenaline tissue content confirmed this.     

The centrosome–Golgi apparatus nexus

A shared feature among all microtubule (MT)-dependent processes is the requirement for MTs to be organized in arrays of defined geometry. At a fundamental level, this is achieved by precisely controlling the timing and localization of the nucleation events that give rise to new MTs. To this end, MT nucleation is restricted to specific subcellular sites called MT-organizing centres. The primary MT-organizing centre in proliferating animal cells is the centrosome. However, the discovery of MT nucleation capacity of the Golgi apparatus (GA) has substantially changed our understanding of MT network organization in interphase cells. Interestingly, MT nucleation at the Golgi apparently relies on multiprotein complexes, similar to those present at the centrosome, that assemble at the cis-face of the organelle. In this process, AKAP450 plays a central role, acting as a scaffold to recruit other centrosomal proteins important for MT generation. MT arrays derived from either the centrosome or the GA differ in their geometry, probably reflecting their different, yet complementary, functions. Here, I review our current understanding of the molecular mechanisms involved in MT nucleation at the GA and how Golgi- and centrosome-based MT arrays work in concert to ensure the formation of a pericentrosomal polarized continuous Golgi ribbon structure, a critical feature for cell polarity in mammalian cells. In addition, I comment on the important role of the Golgi-nucleated MTs in organizing specialized MT arrays that serve specific functions in terminally differentiated cells.     

Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.