Consequences of skin color and fur properties for solar heat gain and ultraviolet irradiance in two mammals

Summary In animals with fur or feather coats, heat gain from solar radiation is a function of coat optical, structural, and insulative characteristics, as well as skin color and the optical properties of individual hairs or feathers. In this analysis, I explore the roles of these factors in determining solar heat gain in two desert rodents (the Harris antelope squirrel,Ammospermophilus harrisi, and the round-tailed ground squirrel,Spermophilus tereticaudus). Both species are characterized by black dorsal skin, though they contrast markedly in their general coat thickness and structure. Results demonstrate that changes in coat structure and hair optics can produce differences of up to 40% in solar heat gain between animals of similar color. This analysis also confirms that the model of Walsberg et al. (1978) accurately predicts radiative heat loads within about 5% in most cases. Simulations using this model indicate that dark skin coloration increases solar heat gain by 5%. However, dark skin significantly reduces ultraviolet transmission to levels about one-sixth of those of the lighter ventral skin.Symbols and abbreviations: (unless noted, all radiation relations refer to total solar radiation) absorptivity of individual hairs - _C absorptivity of the coat - backward scattering coefficient [reflectivity] of individual hairs - _C reflectivity of coat - _S reflectivity of skin - forward scattering coefficient [transmissivity] of individual hairs - _C transmissivity of coat - _S transmissivity of the skin - transmissivity of the coat and skin - transmissivity of the coat to ultraviolet radiation - _S transmissivity of the skin to ultraviolet radiation - [(1 – )² – ²] - h _C coat thermal conductance [W/m²-°C] - h _E coat surface-to-environment thermal conductance [W/m²-°C] - I probability per unit coat depth that a ray will be intercepted by a hair [m^–1] - K volumetric specific heat of air at 20°C [1200 J/m³-°C] - l _C coat thickness [m] - l _H hair length [m] - d hair diameter [m] - n hair density per unit skin area (m^–2] - Q _ABS heat load on animal's skin from solar radiation [W/m²] - Q _I solar irradiance at coat surface [W/m²] - r _E external resistance to convective and radiative heat transfer [s/m] - r _C coat thermal resistance [s/m]     

Alteration of the synthesis of lipoxygenase in the early stages of soybean cotyledon culture

A detailed study of lipoxygenase (EC 1.13.11.12) synthesis in cotyledons of soybean [ Glycine max (L.) Merr. cv. Century] cultured in vitro for up to 40 h showed that synthesis of this protein, measured by in vivo [35S]-methionine labelling in connection with immunological methods and cell-free translation of mRNA, underwent a large transient reduction in the first 4 h of culturing and gradually increased in the following 36 h. Northern blot hybridizations with lipoxygenase cDNA clones showed that the decrease in translational activity was the consequence of a considerable reduction in lipoxygenase mRNA in the cotyledons. From these results we conclude that the transient decline in lipoxygenase synthesis in excised soybean cotyledons is regulated at the RNA level. Similarly judged from the analysis of patterns of uni-dimensional gel electrophoresis, the synthesis of a few other polypeptides decreased during the first 4 h of culture as well, while several others increased; in cotyledons cultured for 20 to 40 h the protein-synthesis pattern had returned to that in freshly excised cotyledons. An acclimation period of ca 1 day seems to be needed for isolated soybean cotyledons to stabilize and to resume regular RNA and protein synthesis.     

Floral-specific polypeptides of the Japanese morning glory

Polypeptides from stems, leaves, sepals, corollas, stamens and pistils of the Japanese morning glory (Ipomoea nil Roth (Pharbitis nil Chois.)) were separated by one- and two-dimensional gel electrophoresis and visualized by silver staining. The majority of polypeptides were expressed in two or more organs, while those specific to only one organ were comparatively rate. Among the polypeptides of the former class were two which appeared to be floral-specific. A 46-kDa (kilodalton) polypeptide was expressed in corollas, stamens and pistils, whereas a 32-kDa polypeptide was observed only in extracts prepared from reproductive organs. Polypeptide spots from the various organs were compared with those from leaves, and it was found that sepals and stems shared 40–50% of their polypeptides with leaves, whereas corollas, stamens and pistils shared 20% or less. The latter organs shared 120 polypeptides or roughly 15% of those identified in the floral extracts. Floralorgan-specific polypeptides comprised nearly 10% of the total floral polypeptides identified.Abbreviations kDa kilodalton - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecylsulfate     

Somatotropin antagonism of insulin-stimulated glucose utilization in 3T3-L1 adipocytes

It is well established that somatotropin (GH) antagonizes insulin action in vivo and that supraphysiologic concentrations of GH frequently result in insulin resistance and glucose intolerance. However, the demonstration of an anti-insulin activity by GH in vitro has been difficult. This study, therefore, set out to determine whether cultures of 3T3-L1 adipocytes could be used to examine the anti-insulin activity of GH. The ability of insulin to stimulate glucose utilization by 3T3-L1 adipocytes increases approximately five-fold during the first 4 days following treatment of the cells with a differentiation medium. It was found that glucose utilization in 3T3-L1 adipocytes is regulated in a reciprocal fashion by insulin and GH. Bovine or human GH directly inhibit up to 50% of insulin-stimulated [14C]-glucose incorporation into lipids in a concentration-dependent manner. The 3T3-L1 sensitivity to GH appears to be at the maximum (50% inhibition of an insulin response) immediately following removal of the cells from the differentiation medium and remains essentially constant during the subsequent 4 days. The GH inhibition of insulin action does not appear to be due GH enhancement of cellular degradation of insulin, competitive binding of GH to the insulin receptor, or GH-induced decrease in cell number. The 3T3-L1 adipocyte system appears to be a sensitive and reliable in vitro model with which to study the molecular mechanisms involved in both GH antagonism of insulin action and development of hormone responsiveness during cellular differentiation into adipocytes.     

Somatic embryogenesis and plant regeneration from zygotic embryo explants in mexican weeping bamboo,Otatea acuminata aztecorum

An efficient protocol has been developed for the in vitro propagation of Mexican Weeping Bamboo through somatic embryogenesis from zygotic embryo explants. Mature seeds and excised embryos were cultured in the light or in the dark on both Murashige and Skoog's and Gamborg's B5 basal media with various supplements. Optimal somatic embryogenesis and plant regeneration were obtained by culture in the dark on Murashige and Skoog's basal medium supplemented with 3 mg/1 2,4-dichlorophenoxyacetic acid, 0.5 mg/1 6-benzylaminopurine and 2.0% sucrose. More than 95% of the germinating somatic embryos developed shoots and roots, and were transferred to soil with 85% success.     

Computational study of radiation chemical processing in comet nuclei

Cometary nuclei have been exposed to high levels of ionizing radiation since their formation. We present here some results of a computer model calculation of the effect of ionizing radiation on cometary material. The external (cosmic rays) and internal (embedded radionuclides) contributions in the processing of cometary nuclei are considered. As a first approximation we have used the available kinetic data of the liquid water system to model the radiation effects in a frozen cometary environment. Out data suggest that massive radiation chemical processing due to cosmic rays may have taken place only in the outer layers of comets. The internal contribution of radionuclides to the radiation processing of comet cores seems to be modest. Therefore, comets could be carriers of intact homochiral biomolecules.Part of this work was carried out during a leave at the Laboratory of Chemical Evolution.     

Functional levels of mitochondrial anion transport proteins in non-insulin-dependent diabetes mellitus

The effect of non-insulin-dependent diabetes mellitus (i.e., NIDDM; type 2 diabetes) on the levels of functional mitochondrial anion transport proteins has been determined utilizing a chemically-induced neonatal model of NIDDM. We hypothesized that moderate insulin deficiency exacerbated by the insulin resistance, which is characteristic of NIDDM, would cause changes in mitochondrial anion transporter function that were similar to those we have previously shown to occur in insulin-dependent diabetes mellitus (i.e., IDDM; type 1 diabetes) (Arch. Biochem. Biophys. 280: 181–191, 1990). Our experimental approach consisted of the extraction of the pyruvate, dicarboxylate and citrate transport proteins from the mitochondrial inner membrane with Triton X-114 using rat liver mitoplasts (prepared from diabetic and control animals) as the starting material, followed by the functional reconstitution of each transporter in a proteoliposomal system. This strategy permitted the quantification of the functional levels of these three transporters in the absence of the complications that arise when such measurements are carried out with intact mitochondria (or mitoplasts). We found that experimental NIDDM did not cause significant changes in the extractable and reconstitutable specific (and total) transport activities of the pyruvate, dicarboxylate, and citrate transporters. These results are in marked contrast to our previous findings obtained using rats with IDDM and negated our hypothesis. The present results, in combination with our earlier findings, allow us to conclude that insulin plays an important role in the regulation of mitochondrial anion transporter function. Accordingly, in this model of NIDDM, where the level of insulin is not profoundly deficient, transporter function is unaltered, whereas in IDDM, where a profound insulinopenia exists, transporter function is altered. Furthermore, the present studies suggest that in the neonatal model of NIDDM the three mitochondrial transporters investigated are neither affected by, nor are they the sites of the well documented hepatic post-receptor insulin resistance which is characteristic of this disease.