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P Hawkins

Publications and source records attributed to P Hawkins.

53 records · Page 3Linked to original sources
PubMed1993

Fast-responding, fibre-optic based sensing system for the volatile anaesthetic halothane, using an ultraviolet absorption technique and a fluorescent film.

An improved version of a fast-responding sensing system for the widely used volatile anaesthetic halothane (2-bromo-2-iodo-1,1,1-trifluoroethane) is described. The concentration of halothane is determined using an ultraviolet radiation (UV) absorption technique. Ultraviolet radiation at 230 nm is conveyed by a silica optical fibre to a gas flow-through cell containing the halothane, and the intensity of the UV reaching the other side of the cell is measured using a fluorescent polymer film. This paper describes the development of an efficient fluorescent polymer film for the sensor based on poly(ethylene glycol) containing two fluorophores (2,5-diphenyloxazole and tris[4,4,4-trifluoro-1-(2-thienyl)butane- 1,3-diono]europium(III)). The film fluoresces strongly with a red line spectrum when excited in the range from about 200 to 380 nm. There is evidence of direct energy transfer between the two fluorophores. A similar effect is observed in films prepared from Carbowax 20M and the europium chelate. An advantage of this approach is that the fluorescent radiation can be transmitted back to a silicon photo-detector using an inexpensive polymer optical fibre bundle. Two experimental sensor systems for halothane are described and the results show that, although the response does not obey the Beer-Lambert law, a reliable system for determining halothane can be constructed, which operates over the medically important range 0-3%. This paper also describes how the signal-to-noise ratio of the system can be improved by using the long fluorescence lifetime of the film.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemistry Techniques, Analytical↗
PubMed1993

External Ca effect on water permeability, regulatory volume decrease, and extracellular space in barnacle muscle cells.

The effect of extracellular Ca2+ (Cao) on sarcolemmal hydraulic water permeability (L'p), regulatory volume decrease (RVD), and extracellular space (ECS) was studied in barnacle muscle cells. Absence or presence of Cao had no effect on L'p [0 Cao = 2.762 +/- 0.098 x 10(-5), and 11 mM Cao = 2.720 +/- 0.222 x 10(-5) cm.kg.s-1 x osmol x 1-kgH2O-1]. Likewise, cells exposed to anisosmotic media (for < 30 min) behaved as osmometers in 0 and 11 mM Cao, showing similar slopes and intercepts in van't Hoff plots. At longer incubation times, however, hyposmotic conditions promoted a Cao-dependent RVD. The relationship between Cao and the percentage of cells responding with RVD to a hyposmotic challenge was sigmoidal (half-maximal Cao = 4.83 mM). The mean rate of RVD (40 nl/min) was independent of the level of swelling in response to hyposmotic challenges. However, the magnitude of RVD increased with larger hyposmotic challenges. Both the presence of Cao and hypotonicity reduced the "apparent" ECS by 47 +/- 6 and 39 +/- 6%, respectively. Three-dimensional reconstruction of autoradiographs of the cells was made to interpret these results.

Animals↗
PubMed1990

The mas oncogene as a neural peptide receptor: expression, regulation and mechanism of action.

The human mas oncogene, which renders transfected NIH/3T3 cells tumorigenic, was identified as a subtype of angiotensin receptor by transient expression in Xenopus oocytes and stable expression in the mammalian neuronal cell line, NG115-401L. The mas receptor preferentially recognizes angiotensin III, and is expressed at high levels in brain. The mas/angiotensin receptor functions through the breakdown of inositol lipids and can drive DNA synthesis, unlike another inositol-linked peptide receptor, that for bradykinin. Comparative analysis of several early biochemical events elicited by either angiotensin or bradykinin stimulation of mas-transfected cells has not indicated a specific difference correlated with mitogenic activity. In particular, the inositol lipid kinase, phosphatidylinositol-3-kinase, thought to be involved in the mitogenic mechanism of platelet-derived growth factor receptors, is unaffected by activation of mas. These results have shown that a proto-oncogene encodes a neural peptide receptor, indicating that peptide receptors may be involved in differentiation and proliferation processes, as are other identified proto-oncogenes.

Amino Acid Sequence↗
PubMed1988

Sperm head structure of a murid rodent from southern Africa: the red veld rat Aethomys chrysophilus.

The morphology of spermatozoa from the red veld rat, Aethomys chrysophilus, of Southern Africa is described; two very different types were found, which came from animals from two separate, as-yet-undescribed, species. In individuals from South Africa the sperm head had a somewhat disc-shaped nucleus and a large acrosome with a huge apical segment that, during epididymal transit, changed in form from initially projecting anteriorly to a highly complex structure that was flexed caudad and lay alongside part of the rest of the sperm head. In addition, the chromatin generally appeared to be not fully condensed. Spermatozoa from animals collected in Malawi were very different in morphology and had a head with a typical apical hook, a perforatorium, fully condensed chromatin, and a 4-micron-long ventral spur. Its sperm tail was also significantly longer. The time of divergence of these two groups of animals from a common ancestor is not known, but the present results show that a considerable morphological change in the sperm nucleus, acrosome, and subacrosomal space can evolve even between two, presumably closely related, species.

Acrosome↗