Crossbridge attachment, resistance to stretch, and viscoelasticity in resting mammalian smooth muscle.

There exist a calcium-dependent resistance to stretch in resting mammalian smooth muscle that is not caused by depolarization of the cell membrane or release of calcium from intracellulr sites. The similarity of the resistance to stretch in the resting state to that in rigor suggests that most, if not all, crossbridges are attached and thus able to resist stretch in noncontracting smooth muscles. When the muscle is stretched the breaking and subsequent reformation of links in nonstrained positions accounts for most of the so-called viscoelasticity, except at extreme lengths.

Modification of photocarcinogenesis by chemical agents.

The evidence is long standing and compelling that chemical agents can modify the carcinogenic effects of light. Various types of chemical-light interaction are discussed, and events in chemical photocarcinogenesis, chemically enhanced photocarcinogenesis, and promotion of photocarcinogenesis are described. Specific examples of each type of process are given, and the importance of interaction of various wavelengths of UV radiation for these processes is stressed.

Simulated stratospheric ozone depletion and increased ultraviolet radiation: effects on photocarcinogenesis in hairless mice.

Solar ultraviolet radiation at the surface of the earth is a recognized cause of skin cancer. Postulated anthropogenic reductions in the thickness of the ozone layer would lead to an increased amount of ultraviolet radiation and hence would be expected to increase the risk of skin carcinogenesis. This study uses hairless (Skh:HR) mice as an animal model to study this increased risk. The mice were exposed 5 days/week to graded doses of ultraviolet radiation from a xenon arc lamp attenuated by five different thicknesses of Schott glass filters (WG320) to simulate various ozone layer thicknesses. A Robertson-Berger sunburning ultraviolet meter was used as one of the forms of dosimetry. The results of the various exposure treatments are expressed as the percentage of animal with tumors (incidence) versus time after commencing irradiation and as cumulative tumor yield (average number of tumors per survivor) versus time. With any given filter, the time to 50% incidence is inversely related to daily dose in Robertson-Berger meter units. The time to 50% incidence for comparable Robertson-Berger meter doses through different filter thicknesses increases with increasing thickness. These results indicate that the effective dose for skin cancer induction may be estimated from the Robertson-Berger meter dose but that the Robertson-Berger meter response spectrum underestimates the photocarcinogenic effectiveness of the shorter wavelengths. The cumulative tumor yield data are also consistent with these conclusions. Alternate weighting of the source spectra with the acute-response action spectrum for mouse skin edema gave a better correlation between unit dose and time to a tumor response, independent of the source spectral distribution. This suggests that the mouse skin edema action spectrum, indistinguishable from a human skin erythema action spectrum for lambda greater than 295 nm, is similar in shape to the mouse skin photocarcinogenesis action spectrum for lambda greater than 295 nm.

Wavelength dependence of skin cancer induction by ultraviolet irradiation of albino hairless mice.

Information on the variation in carcinogenicity with wavelength is crucial in risk assessments for skin cancers induced by UV radiation. Until recently the wavelength (lambda) dependencies of other detrimental UV effects, such as sunburn, have been used as substitutes. Direct information on the lambda dependency can only be obtained from animal experiments. To this end we accumulated a large data set on skin tumors induced by chronic UV exposure of albino SKH:HR1 mice (14 different broadband UV sources and about 1100 mice); the data come from the Photobiology Unit of the former Skin and Cancer Hospital in Philadelphia and from the Department of Dermatology of the University of Utrecht. The lambda dependency was extracted from this data set (a statistically satisfactory description with chi 2 = 13.4, df = 7) and represented by the Skin Cancer Utrecht-Philadelphia action spectrum, i.e., a set of factors to weight the exposures at different wavelengths according to their respective effectiveness (inversely proportional to the daily exposure required for a median tumor induction time of 300 days). The fits obtained with other already available action spectra proved to be poor (chi 2 > 60, df = 11). The maximum effectiveness was found at 293 nm, and above 340 nm the effectiveness showed a shoulder at about 10(-4) of the maximum. A sensitivity analysis of the final solution for the lambda dependency showed a large margin of uncertainty above 340 nm and an information gap below 280 nm. The large variation in tumor responses in the present data set can be transformed to a coherent, common dose-response relationship by proper spectral weighting with this single action spectrum.

Neutral lipids from the skin of the rhino mutant mouse.

The neutral lipids of the skin of the Rhino mutant mouse consist mainly of fatty acid esters of sterols, fatty alcohols and 1,2-alkane diols, with strikingly low amounts of triacylglycerols. Fatty acids of wax and sterol esters were predominantly even chain monounsaturates (63 per cent) between C16 and C36 with a surprisingly high proportion of long chain lengths: the principal peaks corresponded to C32, C34, C18, C30, and C22 monoenes. The fatty alcohols showed a somewhat similar pattern, but with an even greater preponderance of long chain lengths and only small proportions shorter than C24. sterols included cholesterol, as expected, but only to the extent of about 28 per cent; the larger fraction was shown to be lathosterol (5alpha-cholest-7-en-3beta-ol). The largest single fraction (35.6 per cent) of cutaneous lipids consisted of fatty acid esters of 1.2-alkane diols. The 1,2-alkane diols were completely saturated and included odd and even chain lengths, both straight and branched, in the C16-C24 range: predominant peaks were C20, C22(iso), C16, and C22. Fatty acids of diol esters ranged between C14-C36 with major concentrations of C18, C22, C32, and C34 monounsaturates and C20 and C16 saturates.

Triester wax: a novel neutral lipid from the skin of the rhino mutant mouse.

A novel class of neutral lipids has been isolated from the skin of the rhino mutant mouse and has been characterized as a triester wax. The lipid, on saponification and transesterification, yielded fatty acids, omega-hydroxy fatty acids and 1,2-alkane diols. These products were identified by gas-liquid and thin-layer chromatography, infrared, nuclear magnetic resonance and mass spectroscopy, combined gas-liquid chromatography and mass spectrometry and chemical methods. Fatty acids were found to be predominantly of even chain length between C14 and C36 with highest concentration at C22 : 1. Hydroxy fatty acid methyl esters (trimethylsilyl ether derivatives) showed the presence of only three components in the relative abundance of 9: 70 : 21. The structure of the major component was established as 34-hydroxytetratricont-25-enoic acid and the other two components were characterized as 32-hydroxyditricont-23-enoic and 36-hydroxyhexatricont-27-enoic acids. In addition to these omega-9 unsaturates, other isomers having unsaturation at omega-7 and omega-8 were also present in small amounts. The 1,2-alkane diols were predominantly saturated in the range of C16-C24.

Chemical energetics of force development, force maintenance, and relaxation in mammalian smooth muscle.

High-energy phosphate utilization (delta approximately P) associated with force development, force maintenance, and relaxation has been determined during single isometric tetani in the rabbit taenia coli. ATP resynthesis from glycolysis and respiration was stopped without deleterious effects on the muscle. At 18 degrees C and a muscle length of 95% l0, the resting rate of energy utilization is 1.8 +/- 0.2 nmol/g . s-1, or 0.85 +/- 0.2 mmol approximately P/mol of total creatine (Ct) . s-1, where Ct = 2.7 mumol/g wet wt. During the initial 25 s of stimulation when force is developed, the average rate of delta approximately P was -8.2 +/- 0.8 mmol/mol Ct . s-1, some four times greater than during the subsequent 35 s of force maintenance, when the rate was -2.0 +/- 0.6 mmol approximately P/mol Ct . s-1. The energy cost of force redevelopment (0 to 95% P0) after a quick release from the peak of a tetanus is very low compared with the initial force development. Therefore, the high rate of energy utilization during force development is not due only to internal work done against the series elasticity nor to any high rate of cross-bridge cycling inherently associated with force development. The high economy of force maintenance compared with other muscle types is undoubtedly due to a slower cross-bridge cycle time. The energy utilization during 45 s of relaxation was not statistically significant, and integral of Pdt/delta approximately P was higher during relaxation than during force maintenance in the stimulated muscle.

Aging, environmental influences, and photocarcinogenesis.

Repeated exposure of human skin to solar ultraviolet radiation (UVR) over a period of many years is responsible for the induction of most nonmelanoma skin cancers in man. The tumors are progressively more common in chronologically older people. Is this fact purely a function of adequate dose accumulation and development time, or is tumor expression influenced by "physiological age"? The answer to this question influences risk estimates of the results of atmosphere modification. Data from animal studies indicate that the tumor incidence is affected by dose-delivery factors and not just by the accumulated lifetime dose. In addition, young mice are more prone to tumor induction by a given UVR dose than are older animals. Because the quanlity and quantity of the stimulus (UVR) can be readily manipulated and accurately described, studies on photocarcinogenesis offer distinct possibilities for untangling some of the interactive variables in the aging process.

Cutaneous photobiology: past, present and future.

The history and origin of the science of photobiology are reviewed. Interest in the biologic effects of light gradually increased, beginning with the discovery of ultraviolet and infrared radiation early in the 19th century. The basis of experimental photobiology was laid by the studies of Raab and Tappeiner on photodynamic action and the early uses of phototherapy by Finsen and Dorno. The discovery of the association of porphyrins with some light-related skin diseases and of the capability of chemical agents such as coal tar and bergamot to induce phototoxic contact dermatitis resulted in a flurry of clinical investigations leading to better understanding of the processes of phototoxicity and photoallergy. The early epidemiologic studies of Unna and Dubreuilh relating solar radiation exposure to the formation of actinic keratoses and non-melanoma skin cancer were experimentally confirmed in animals by Findlay, Roffo, and Blum. In the most recent quarter century (1950-1975), cellular and molecular photobiology has been refined. The studies on photochemistry of nucleic acid and of damage and repair mechanisms in DNA have set the stage for understanding the basic processes of biologic effects of light and promise the development of useful applications of specifically directed phototherapy and prevention of such light-induced diseases as skin cancer.

Enhancement of experimental photocarcinogenesis by topical retinoic acid.

Topical application of retinoic acid (RA) solutions greatly enhanced the response of hairless mouse skin to a moderate dose of simulated sunlight. Tumors appeared much earlier, and in much greater numbers, in animals treated daily with 1 or 10 micrograms of RA in methanol immediately after 2 h exposure to a xenon arc filtered through 2 mm of Schott WG 320 glass (approximately equivalent in human erythema effectiveness to 5 min of mid-summer noon solar exposure in northern mid-latitudes), compared to mice treated with light and methanol only. The higher amount of RA, in combination with light, produced moderate epidermal hyperplasia and some scaling and transient erythema, but no gross ulceration or inflammation of skin. The lower amount of RA, though about equally effective in carcinogenesis, produced minimal epidermal hyperplasia compared to the ultraviolet radiation + methanol control.

Effect of indoor lighting on normal skin.

A small but measurable component of some indoor lighting is ultraviolet radiation (UVR); whether it is sufficient to modify the indoor worker's risk for chronic skin changes is not directly answerable with available technology. A first approach to this question involves a) estimating a range of annual background solar exposure for indoor workers currently at risk; b) determining whether, and at what levels, UVR exposure is a part of specified indoor lighting; and c) calculating the increment in risk implied by a and b. This algorithm predicts that some lighting conditions that meet NIOSH recommended standards would still result in significant increases in the risk of cumulative UVR damage, including skin cancer. More information concerning actual exposure conditions, the relation of spectral effectiveness for luminosity and UVR production, and dose-time reciprocity are required to improve our predictions of long-term cutaneous effects of indoor lighting.

A comparison of the effects of capsaicin with inhibitory nerve stimulation in the rat anococcygeus muscle in vitro.

Capsaicin was used to test whether centrifugal activation of sensory fibres in the rat anococcygeus muscle can contribute to non-adrenergic non-cholinergic (NANC) relaxation of the muscle. In a solution containing 0.5 mM Ca2+ and in the presence of carbachol (10 microM) capsaicin evoked a fast concentration-dependent relaxation of the muscle that was usually followed by a smaller, slower, relaxant response. The fast relaxant response was reduced when extracellular Ca2+ was raised to 2.5 mM, desensitized after a single application of capsaicin and was blocked by tetrodotoxin (1 microM) or ruthenium red (10 microM). The fast response was greatly reduced by haemoglobin, by cold storage of the muscles or by N-monomethyl-L-arginine (100 microM) in the absence but not in the presence of L-arginine (100 microM). It is concluded that centrifugal activation of sensory fibres evokes a nitric oxide-mediated relaxation of the anococcygeus muscles that probably contributes to electrically evoked NANC relaxation.

The toxicity of dimethyl sulphoxide (DMSO) for the dog, pig, rat and rabbit.

Dimethyl sulphoxide (DMSO) was tested for oral toxicity in rats and dogs, and dermal toxicity in rabbits and pigs. Oral administration was by gastric intubation as a 50% equeous solution, 5 days/week at levels equivalent to 9.0, 3.0 or 1.0 ml undiluted DMSO/hg/day. For dermal application 50% and 90% equeous solutions were used to give levels equivalent to 8.1, 4.5, 2.7 or 1.5 ml DMSO/hg/day, as one daily application for rabbits, and divided into two applications/day for pigs. Dogs were dosed for approximately 2 years and pigs for 1 year, although half the animals of both species were dosed for only 18 weeks. Rats were dosed for 18 months, but some were used for interim sacrifice after a year. Rabbits received applications to normal and abraded skin for 6 months. Minor changes in bodyweight and haematological values were observed, together with a physiological diuretic response to DMSO, but the target organ was the eye, principally the lenticular nucleus. Ocular effects in dogs started after 5-10 weeks dosing at 9 ml/kg and consisted of central (nuclear) lens changes with alteration of the refractive index (myopia); transitory equatorial opacities during the 5th month; central (nuclear) opalescence; and changes in the vitreous humour. Similar changes occurred more slowly at 3 ml/kg, the alterations to the vitreous being first observed after 9-10 months at this level. Progressive nuclear refractive changes occurred after dosing for considerably longer than 6 months at 1ml/kg, but none of the animals in this group manifested the opalescence. Biochemical investigation of the lenses revealed reduction of soluble protein (mainly alpha-crystallin), glutathione and water levels, and an increase of insoluble protein. Evidence of recovery was limited mainly to a reduction in the number of dioptres needed to correct nuclear refractive change. Cessation of dosing led to regression of refractive nuclear changes but did not prevent the appearance of opalescence at 3 ml/kg and above. Dogs were the most severely affected of the 4 species, with nuclear effects at 1ml/kg, extensive changes in the lens, and involvement of the vitreous. Pigs and rabbits were affected by dose levels of 2.7 ml/kg and 1.5 ml/kg respectively. Rats occasionally showed minimal changes at 9 ml/kg. The importance of the findings in dogs is discussed in relation to general toxicological protocols. It is emphasised that reversibility of signs, and adequate duration of administration, must both be considered when ascertaining whether changes occur at levels approximating to those of human intake.

Diesters of alkane diols and 2-hydroxy fatty acids: identification and discrimination of isomers with the aid of NMR spectroscopy.

High resolution nuclear magnetic resonance spectroscopy has been shown to be extremely useful for the identification and discrimination of naturally occurring diesters of 1,2- and 2,3-alkanediols as well as for fatty alkyl esters of acylated 2-hydroxy fatty acids. A comparison of 220 MHz spectra of 1,2 and erythro- 2,3-alkanediol diesters exhibits the following distinguishing features: (1) two non-equivalent methylene protons from the glycol group of 1,2-alkanediol diesters resonate at 3.87 ppm and 4.17 ppm respectively while these resonances are completely absent in the spectrum of 2,3-isomer; (2) methylene protons adjacent to esther carbonyl groups appear as two overlapping triplets at 2.22 ppm in 1,2-alkanediol diesters while the corresponding protons in the 2,3-isomer are displayed as two partially overlapping triplets centered at 2.15 ppm and 2.2 ppm respectively; and (3) methyl protons adjacent to glycol group in 2,3-isomer appear as downfield doublet at 1.13 ppm; this downfield doublet is not shown by 1,2-alkanediol diesters. Erythro- and threo-2,3-alkanediol diesters have also been distinguished from each other; two alpha-methylenes in erythro isomers appear as partially overlapping triplets while these protons in threo isomer display an apparent quartet centered at 2.22 ppm. Fatty alkyl esters of acylated 2-hydroxy fatty acids display a triplet at 4.79 for 2-position methylene proton, a distinguishing feature not shown by diacyl alkanediols. A distinction between diester lipids and other classes of neutral lipids has also been achieved by the study of nuclear magnetic resonance spectra, particularly in the region of 3-6 ppm.

A selective Pt-CdS photodiode to monitor erythemal flux.

The design and potential benefit of a solar ultraviolet (UV) radiometer reporting a maximum instantaneous flux of erythemally weighted heterogeneous energy is considered. The proposed device is electronically peak detecting; the user would ideally 'point and paint' the sun to find a localized maximum. A projected exposure time can be calculated from an instantaneous reading of erythemally weighted flux for a given minimal erythemal dose (MED) specified by the user. This calculation, though not necessarily providing a true exposure time, may be useful and informative in that it serves as a more 'recognizable' measure of erythemal flux and introduces a custom scale for each individual via their MED. Erythemal flux is calculated as the weighted integral sum [symbol: see text]j(lambda,t) epsilon(lambda) d lambda, where j (lambda, t) is the instantaneous angular integrated spectral irradiance accepted by human skin. This instrument proposal uses a single interference filter over a Pt-CdS photodiode; the interference filter is offered as a nominal design transmittance. The simulated response of the selective photodiode has a near-linear relation to the effective irradiance. Test inputs for evaluation purposes and to elucidate a transducer response are constructed from a spline interpolation of the World Radiation Center (WRC) spectrum and classic transmittance models. Our desired erythemal flux is offered in interconvertible UV Indexes (UVIs) as a function of zenith angle and atmosphere, characterized by elevation, ozone path, and turbidity.

Skin-tumour promoting activity of methyl ethyl ketone peroxide--a potent lipid-peroxidizing agent.

The tumour-promoting activity of methyl ethyl ketone peroxide (MEKP) was tested on the skin of hairless mice using a two-stage initiation-promotion protocol. When ultraviolet radiation in the UVB region (280-320 nm) was used as tumour initiator, MEKP showed weak promoting activity. The promotional activity of MEKP was potentiated by diethyl maleate, which is known to deplete intracellular glutathione, suggesting that lipid peroxidation may be important in the tumour promotion.

Lipid oxidation: biologic effects and antioxidants--a review.

The detection and measurement of lipid oxidation in biological systems and some biologic effects of this oxidation are reviewed. The role of lipid oxidation in the process of photocarcinogenesis and the protective effect of antioxidants against this process also are discussed. The mechanism of such protection is unknown and studies directed at elucidating the mechanism of antioxidant effect in photocarcinogenesis and in some other pathological conditons believed to involve lipid oxidation are needed. In addition to this, epoxidation of lipids observed in monolayer studies requires further investigation, particularly in the presence of some other unsaturated molecules. The possible significance of such a study--particularly in the presence of polycyclic aromatic hydrocarbon carcinogens, where formation of epoxides is generally accepted as active intermediates--is also discussed. In addition, present knowledge on the role of lipid peroxides in the destruction of proteins and biomembranes, in chemically induced toxicity and in generation of singlet oxygen is presented.

Effect of antioxidants on the photooxidation of fatty acids.

The effect of butylated hydroxytoluene (BHT), butylated hydroxy anisole (BHA) and tocopherol acetate on photooxidation of the fatty acids was studied. A marked increase in the photooxidation was observed in the presence of BHT, and this effect was further potentiated by hexabromobiphenyls. Conversely, BHA and tocopherol acetate as such did not show any significant effect, but greatly enhanced the photooxidation when hexabromobiphenyls were also present. Hexabromobiphenyls by themselves did not show any notable effect on the photooxidation.