Biomedical subjects

J A Firth

Publications and source records attributed to J A Firth.

57 records · Page 4Linked to original sources

PubMedDate not supplied

Histochemical localization of phosphatases in the pig placenta: II. Potassium-dependent and potassium-independent p-nitrophenyl phosphatases at high pH; relation to sodium-potassium-dependent adenosine triphosphatase.

Histochemical localization by Mg2+ capture methods of K+-dependent, ouabain-sensitive phosphatase activity in the pig placenta shows that strong Na+,K+-dependent adenosine triphosphatase (Na+,K+-ATPase) activity is restricted to the basal zone of the columnar epithelium covering the areolar chorionic villi. It is proposed that active Na+ absorption at this epithelium may be the source of the ouabain-sensitive, fetal-side-positive potential difference which can be measured across the placental membrane in vitro. The one-step procedure for Na+,K+-ATPase localization is unsatisfactory in this organ as any specific ATPase reaction is swamped by activity probably attributable to uteroferrin and other non-specific phosphatases.

4-Nitrophenylphosphatase↗

PubMedDate not supplied

Not trophoblast alone: a review of the contribution of the fetal microvasculature to transplacental exchange.

The fetal microcirculation of the term human placenta offers an interesting microvascular model. A perfused placenta can be used for integrated studies of vascular permeability-structure relationships. The organization of the paracellular pathway in human placental microvessels closely resembles not only that of the guinea-pig placenta, but also that seen in typical continuous non-cerebral capillaries such as those of the myocardium. This uniformity of organization has allowed the development of a model of the organization of endothelial junctional complexes that allows testable predictions about the relationship between junctional organization and microvascular permeability. The key features of this model are: (1) molecular size restriction may be determined by a fibre matrix based on cadherin arrays in the zonula adhaerens. (2) The zonula occludens (tight junction) is discontinuous and so cannot act as a molecular sieve for solutes. It may serve as a shutter that limits the proportion of the paracellular cleft available for permeation. The main implication for placental function is that the human placental microcirculation is relatively tight and is an important restriction to diffusive permeation of the maternal-fetal barrier by large molecules.

Animals↗

PubMedDate not supplied

Focal and regional variations in the composition of the glycocalyx of large vessel endothelium.

The glycocalyx of the endothelium of the systemic arteries and vena cava of the rabbit was visualised by in situ perfusion fixation with glutaraldehyde containing Alcian blue. The thickness of the layer ranged from 45 +/- 1 nm in the coronary artery to 81 +/- 2 nm in the carotid. The glycocalyx was 20 +/- 1.5 nm thicker on the downstream side of intercostal ostia than on the upstream side. Changes in the staining pattern with increasing concentrations of MgCl2 indicated that carboxyl groups made the major contribution to the surface charge, though sulphate groups were also present, particularly in the aortic arch and carotid artery. Segments of the thoracic aorta and carotid artery were also stained in vitro with fluorescence labelled wheat germ agglutinin, and fluorescence intensity in histological sections was quantified using a video microscope equipped with a microcomputer-based image analysis system. The fluorescence intensity in the carotid was 1.65 +/- 0.15 times that in the aorta. Pretreatment with neuraminidase reduced fluorescence intensity by 60 +/- 4% in the carotid and 53 +/- 2% on the upstream side of intercostal ostia, but only by 37 +/- 3% on the downstream side. Chondroitinase and heparanase both reduced binding and when used together their effect was additive, reducing fluorescence by 27 +/- 3, 51 +/- 4, and 32 +/- 3% at the three sites, respectively. Though the interpretation of the lectin binding experiments is complicated by a number of factors, these results support previous reports that sialyl groups are abundant in the endothelial glycocalyx. Glycosaminoglycans are also present, however, in significant amounts.

Alcian Blue↗