Longitudinal associations between parental reflective functioning and maternal mind-mindedness

Little work has examined longitudinal associations between parental reflective functioning (PRF) and mind-mindedness (MM), limiting the understanding of separate or bidirectional trajectories of these related but distinct forms of mentalization. We examined cross-lagged associations between PRF, assessed via interview, and MM, coded from play interactions, over 12 months among 90 parents (86% female; 57% White, 43% Black) of infants (Mage = 10.56 months, SD = 8.20) who were participating in The Michigan Model of Infant Mental Health Home Visiting. Data were collected at study enrollment Time 1 (T1) and at 6-month Time 2 (T2) and 12-month Time 3 (T3) postenrollment. Mind-minded comments were coded as appropriate, reflecting accurate interpretation of mental states or nonattuned, characterizing inaccurate interpretations. PRF and appropriate MM each remained stable over time. PRF at the T1 positively predicted appropriate MM at T2. No other cross-lagged associations between PRF and appropriate MM were significant. Concurrent correlations between appropriate MM and PRF were significant only at T3. Nonattuned MM showed stability from T1 to T2 but nonattuned MM at the T2 did not predict nonattuned MM at T3. Greater PRF at T1 predicted less nonattuned MM at T2. No other cross-lagged associations between PRF and nonattuned MM were significant. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Physical activity and survival after cancer diagnosis in men

BACKGROUND

The number of cancer survivors is increasing rapidly; however, little is known about whether engaging in physical activity after a cancer diagnosis is associated with lower mortality rates in men.

METHODS

We conducted a prospective cohort study of 1021 men (mean age, 71.3 years) who were diagnosed with cancer (other than nonmelanoma skin cancer). Men reported their physical activities (walking, stair climbing, and participation in sports and recreational activities) on questionnaires in 1988, a median of 6 years after their cancer diagnosis. Physical activity was updated in 1993 and men were followed until 2008, with mortality follow-up > 99% complete, during which 777 men died (337 from cancer, 190 from cardiovascular disease).

RESULTS

In multivariate analyses, the relative risks for all-cause mortality associated with expending < 2100, 2100-4199, 4200-8399, 8400-12,599, and ≥ 12,600 kJ/week in physical activity were 1.00 (referent), 0.77, 0.74, 0.76, and 0.52, respectively (P-trend < 0.0001). Higher levels of physical activity also were associated with lower rates of death from cancer and cardiovascular disease (P- trend = 0.01 and 0.002, respectively).

CONCLUSIONS

Engaging in physical activity after cancer diagnosis is associated with better survival among men.

Nitric oxide-proton stimulation of trigeminal ganglion neurons increases mitogen-activated protein kinase and phosphatase expression in neurons and satellite glial cells

Elevated nitric oxide (NO) and proton levels in synovial fluid are implicated in joint pathology. However, signaling pathways stimulated by these molecules that mediate inflammation and pain in the temporomandibular joint (TMJ) have not been investigated. The goal of this study was to determine the effect of NO-proton stimulation of rat trigeminal neurons on the in vivo expression of mitogen-activated protein kinases (MAPKs) and phosphatases (MKPs) in trigeminal ganglion neurons and satellite glial cells. Low levels of the active MAPKs extracellular signal-regulated kinase (ERK), Jun amino-terminal kinase (JNK), and p38 were localized in the cytosol of neurons and satellite glial cells in unstimulated animals. However, increased levels of active ERK and p38, but not JNK, were detected in the cytosol and nucleus of V3 neurons and satellite glial cells 15 min and 2 h following bilateral TMJ injections of an NO donor diluted in pH 5.5 medium. While ERK levels returned to near basal levels 24 h after stimulation, p38 levels remained significantly elevated. In contrast to MKP-2 and MKP-3 levels that were barely detectable in neurons or satellite glial cells, MKP-1 staining was readily observed in satellite glial cells in ganglia from unstimulated animals. However, neuronal and satellite glial cell staining for MKP-1, MKP-2, and MKP-3 was significantly increased in response to NO-protons. Increased active ERK and p38 levels as well as elevated MKP levels were also detected in neurons and satellite glial cells located in V2 and V1 regions of the ganglion. Our data provide evidence that NO-proton stimulation of V3 neurons results in temporal and spatial changes in expression of active ERK and p38 and MKPs in all regions of the ganglion. We propose that in trigeminal ganglia these cellular events, which are involved in peripheral sensitization as well as control of inflammatory and nociceptive responses, may play a role in TMJ pathology.

Delivering home-based case management to families with children with mental retardation and developmental disabilities

To meet the needs of individuals with mental retardation and developmental disabilities (MR/DD) and their families living in urban setting, a noncenter-based model of case management was implemented. In contrast to traditional case management in which families and consumers come to the case manager and most service coordination is done by telephone or in meetings at the case manager/social worker's worksite, the case manager in a noncenter-based model is mobile and able to meet the consumer and family in their domains. In this model, case management is provided in conjunction with in-home residential habilitation and funded by Medicaid under the Home and Community Based Services Waiver. This funding stream provides monies for nontraditional services delivered in noncertified settings. Case managers used the Family Resource Scale to get an immediate indication of the resources and needs of each family. The scale highlights the adequacy of a person's basic and caregiving resources, as well as financial needs. The findings from this study suggest that an understanding of both disability and entitlements is essential for case managers who may have to help advocate for consumers around services and benefits. Moreover, to build and maintain an egalitarian and supportive relationship with families, the importance of caregiver-specified resources and needs must be recognized by case managers. Access to resource information and the ability to engage the family in problem-solving depends on a well-trained staff with the ability to respond to individuals with different needs and from a variety of circumstances. These essential skills prepare a case manager to assist families with their immediate requirements as well as to mobilize them to plan for future needs.

The biological hazards of plutonium

The health hazards associated with exposure to low levels of plutonium are reviewed since, though the world may escape a nuclear war, there may be virtually permanent contamination of the biosphere by plutonium from a number of sources. It would seem that it is possible to offer workers in the nuclear industry an acceptable level of protection but that low levels of pollution around such sites may build up until there is a hazard for people in the vicinity. The cases of childhood leukaemia found in the vicinity of the Sellafield facility may or may not be related to contamination in the area; however, plutonium is a potent carcinogen, and the foetus seems to be particularly vulnerable to it. The disposal of nuclear waste must be monitored more closely, and it is suggested that the International Atomic Energy Agency should take on this added responsibility.

Effects of some organophosphorus compounds on the binding of a radioligand (8-cyclopentyl 1, 3-[3H]dipropylxanthine) to adenosine receptors in ovine cardiac membranes

8-Cyclopentyl-1,3-[3H] dipropylxanthine [( 3H]CPX) is a potent radioligand that specifically binds to the A1 adenosine receptors. Its high specificity makes it a suitable ligand for the characterization of A1 adenosine receptors in tissues with low receptor densities. We have demonstrated that the organophosphorus compounds soman, tabun and sarin, at relatively high concentrations, all bind to the A1 adenosine receptors in ovine cardiac membranes with Ki values of 36.7, 328 and 175 microM, respectively. The binding of soman to the receptor site was found to be totally reversible. We suggested that these organophosphorus compounds affect the mechanical responses of the heart through interaction with a potassium channel that does not seem to be closely linked to the A1 adenosine receptors.

DNA damage in cultured human skin fibroblasts exposed to excimer laser radiation

Ultraviolet excimer lasers are being considered for use in a variety of refractive and therapeutic procedures, the long-term biologic consequences of which are unknown. The effect of sublethal doses of 193-nm laser radiation on cellular DNA was examined in cultured human skin fibroblasts. In contrast to 248 nm, treatments with the 193-nm laser radiation below 70 J/m2 did not cause significant pyrimidine dimer formation in the skin cells. This was indicated by the lack of excision repair activities (unscheduled DNA synthesis assay), and further demonstrated by direct analysis of pyrimidine dimers in DNA from irradiated cells. However, a low level of unscheduled DNA synthesis could be detected following irradiation at 193 nm with 70 J/m2. Both the 193-nm and 248-nm radiation were able to induce chromosomal aberrations, as indicated by a micronucleus assay. A dose-dependent increase in micronuclei frequency was observed 48 and 72 h after laser irradiation. These results indicate that exposure of actively replicating human skin fibroblasts to sublethal doses of either 193- or 248-nm laser radiation can result in genotoxicity.

Do pyrimidine dimer yields correlate with erythema induction in human skin irradiated in situ with ultraviolet light (275-365 nm)?

Ultraviolet radiation produces erythema in human skin, and damages the DNA of living cells in skin. Previous work showed that broad-band UV-B (290-320 nm) radiation produced higher levels of cyclobutyl pyrimidine dimers in DNA of individuals with high UV-B sensitivity (low minimal erythema dose) than in subjects of low UV-B sensitivity [Freeman et al. (1986) J. Invest. Dermatol., 86, 34-36]. We examined the relationship between erythema induction and dimer yields in DNA of human skin irradiated in situ with narrow band radiation spanning the wavelength range 275-365 nm. We find that, in general, higher dimer yields are produced per incident photon in volunteers with higher susceptibility to erythema induced by radiation of the same wavelength.

Is the inhibitory effect of somatostatin on the heart due to K+ channel activation?

1. Somatostatin (SS) was found to shorten the action potential of both left and right atrium, and to reduce the force of contraction of the atrium. Action potential shortening was antagonized by the potassium channel blocking drugs tacrine and apamin. They were less effective in reducing the negative inotropic effect of SS. 2. Alkylation of the intact atrium with N-ethylmaleimide abolished both the AP shortening and the negative inotropic effect of SS. 3. Pretreatment of guinea pigs with pertussis toxin abolished the negative inotropic effect of SS and reduced the AP shortening. 4. Binding studies showed there was virtually no interaction between SS and muscarinic and adenosine receptors. 5. It is suggested that the cardiac SS receptor is linked with G protein-K+ channel-adenylyl cyclase system which is analogous to but not identical with the muscarinic and adenosine receptor systems.

Present state of control of chemical and biological weapons

The use of chemical and biological weapons in war is prohibited by the Geneva Protocol of 1925 and the Biological Weapons Convention of 1972. Currently a new Chemical Weapons Convention is being negotiated in the UN Conference on Disarmament in Geneva. When this Convention enters into force the production, stockpiling and retention of chemical weapons will be prohibited. The development of a body of international law will enable the verifiable destruction of weapons such as these, and should lead to a more general programme of disarmament.

Excision repair of pyrimidine dimers induced by simulated solar radiation in the skin of patients with basal cell carcinoma

One prominent lesion induced in DNA by ultraviolet (UV) radiation is the cyclobutyl pyrimidine dimer formed between adjacent pyrimidines on the same DNA strand. We investigated whether people who have developed basal cell carcinoma on sun-exposed skin have an altered ability to repair UV-induced pyrimidine dimers in DNA. Twenty-two patients with at least one basal cell carcinoma, aged 31-84 years, and 19 healthy volunteers, aged 25-61 years, took part in the study. Both groups were given one minimal erythema dose (MED) of simulated solar radiation on the lower back. DNA was extracted from the irradiated skin 0 to 6 h later, and the number of UV-induced pyrimidine dimers was determined using a dimer-specific endonuclease. At time 0, the average number of dimers per unit of DNA was similar in the two groups. After 6 h, an average of 22 +/- 4% of the dimers were removed in the group with basal cell carcinoma compared to 33 +/- 4% in the cancer-free group. In the basal cell carcinoma group, only 23% of the patients repaired more than 30% of the dimers after 6 h, compared with 53% of the cancer-free subjects (p less than 0.05). We conclude that patients who develop basal cell carcinoma on sun-exposed skin may have a decreased ability to repair pyrimidine dimers induced in skin exposed to simulated solar radiation.

Does exposure of human skin in situ to 385 or 405 nm UV induce pyrimidine dimers in DNA?

A previous report [Freeman et al. (1986) Photochem. Photobiol. 43S, 93S] indicated that irradiation of human skin in situ with 385 or 405 nm radiation produced detectable levels of pyrimidine dimers in DNA. Since these wavelengths are absorbed poorly by DNA, these results suggested that DNA damage was sensitized by other absorbing molecules present in skin. Examination of two experimental aspects of the previous work indicates that (1) the static gel electrophoresis method for DNA dispersion used in lesion determination gave accurate values of the levels of induced dimers, and (2) the DNA damage apparently induced by 385 nm was actually induced by shorter wavelength UV present in the 20 nm bandpass beam of the monochromator. The current results indicate that monochromatic 385 and 405 nm radiation are ineffective in dimer production in human skin in situ.

Wavelength dependence for UV-induced pyrimidine dimer formation in DNA of human peripheral blood lymphocytes

An action spectrum for the induction of pyrimidine dimers in human peripheral lymphocytes was determined between 254 and 405 nm. The presence of pyrimidine dimers was determined as UV-induced lesions that were sensitive to the dimer-specific endonuclease from Micrococcus luteus in conjunction with agarose gel electrophoresis. The rate of induction of pyrimidine dimers was maximal at 254 nm. These values can be compared with action spectra for UV-induced in vitro responses of lymphocytes.

Electrophoretic separation of nucleic acids: evaluation by video and photographic densitometry

The separation of DNA by gel electrophoresis provides a rapid method for determining size distributions of DNA in solution. Densitometric scanning of photographs of gels has been the standard method of analysis of agarose gels. However, analysis of photographs is complicated by the non-linear response of photographic film. Charged-coupled device video cameras have become popular for quantitative densitometry and we have used a charge-coupled device camera to image agarose gels to quantitate DNA damage. We compare video and photographic densitometry for quantitation of ultraviolet radiation (UV)-induced DNA damage and find that the two methods give equivalent results.

Quantitation of ultraviolet radiation-induced cyclobutyl pyrimidine dimers in DNA by video and photographic densitometry

We have compared video and photographic methods for calculating the number of ultraviolet radiation (uv)-induced pyrimidine dimers in DNA from the bacteriophage T7 exposed to uv (0 to 800 J/m2) from an FS40 sunlamp. DNA was incubated with a pyrimidine dimer-specific Micrococcus luteus uv endonuclease, subjected to alkaline agarose gel electrophoresis, neutralized, and stained with ethidium bromide, and the DNA fluorescence was recorded either with a video camera or on photographic film. The slopes of the dose-response curves for the number of uv-endonuclease-sensitive sites per 10(3) bases (pyrimidine dimers) was 1.2 (+/- 0.1) X 10(-4) uv-endonuclease-sensitive sites per J/m2 for the video analysis and 1.3 (+/- 0.04) X 10(-4) uv-endonuclease-sensitive sites per J/m2 for the photographic analysis. Results for pyrimidine dimer determination by either method were statistically comparable.

Wavelength dependence of pyrimidine dimer formation in DNA of human skin irradiated in situ with ultraviolet light

The UV components of sunlight are believed to be a major cause of human skin cancer, and DNA is thought to be the principal molecular target. Alterations of the intensity and wavelength distribution of solar UV radiation reaching the surface of the earth, for example by depletion of stratospheric ozone, will change the effectiveness of solar radiation in damaging DNA in human skin. Evaluation of the magnitude of such effects requires knowledge of the altered sunlight spectrum and of the action spectrum for damaging DNA in human skin. We have determined an action spectrum for the frequency of pyrimidine dimer formation induced in the DNA of human skin per unit dose of UV incident on the skin surface. The peak of this action spectrum is near 300 nm and decreases rapidly at both longer and shorter wavelengths. The decrease in our action spectrum for wavelengths less than 300 nm is attributed to the absorption of the upper layers of the skin, an in situ effect that is inherently included in our measurements. Convolution of the dimer action spectrum with the solar spectra corresponding to a solar angle of 40 degrees under current levels of stratospheric ozone (0.32-cm O3 layer) and those for 50% ozone depletion (0.16-cm O3 layer), indicate about a 2.5-fold increase in dimer formation. If the action spectrum for DNA damage that results in skin cancer resembles that for dimer induction in skin, our results, combined with epidemiological data, suggest that a 50% decrease in stratospheric ozone would increase the incidence of nonmelanoma skin cancers among white males in Seattle, Washington, by 7.5- to 8-fold, to a higher incidence than is presently seen in the corresponding population of Albuquerque, New Mexico.

Sunscreen protection against UV-induced pyrimidine dimers in DNA of human skin in situ

We have determined the ability of a chemical sunscreen with a sun protection factor (SPF) of 15 to protect human skin from ultraviolet (UV) radiation-induced DNA damage. The DNA damage was susceptible to cleavage by Micrococcus luteus UV endonuclease, which recognizes pyrimidine dimers in DNA. An alkaline agarose gel electrophoresis method was used to quantify the number of pyrimidine dimers in nonradioactive DNA from skin biopsies of 5 individuals irradiated with UV from a solar simulator. After exposure to an equivalent dose of UV, the number of pyrimidine dimers was 0.8 per 10(7) bases in sunscreen-treated skin as compared with 32 dimers per 10(7) bases in untreated skin. This assay provides a means of determining the efficacy of sunscreens in protecting skin from UV-induced DNA damage.

Binding of some organophosphorus compounds at adenosine receptors in guinea pig brain membranes

The organophosphorus compounds, sarin, tabun and soman are known to be potent inhibitors of cholinesterase. It was claimed that these agents also interact at neurotransmitter receptor sites. We were unable to detect any interaction at the acetylcholine muscarinic sites; we now focus our attention on the adenosine receptors. Binding studies showed that all three anticholinesterases inhibited the binding of [3H]L-phenylisopropyladenosine ([3H]L-PIA) to the brain adenosine receptors in a dose-dependent manner until receptor concentration became limiting. Soman was found to be 5 and 9 times more effective than tabun and sarin respectively in inhibiting [3H]L-PIA binding. These results suggested that these organophosphorus anticholinesterases could interact directly at the A1 adenosine receptors which could subsequently mediate changes in K+ permeability of synaptic membranes.

Excision repair of pyrimidine dimers in human peripheral blood lymphocytes: comparison between mitogen stimulated and unstimulated cells

Excision repair kinetics of UV-induced pyrimidine dimers in DNA of phytohemagglutinin (PHA)-stimulated human peripheral blood lymphocytes were compared to unstimulated lymphocytes using a dimer-specific endonuclease from Micrococcus luteus in conjunction with agarose gel electrophoresis. Removal of pyrimidine dimers could be detected within 6 h after irradiation only in PHA-stimulated lymphocytes. However, incorporation of [3H]thymidine as UV-induced unscheduled DNA synthesis was detected in the unstimulated lymphocytes in the 6-h period. The number of pyrimidine dimers remaining in unstimulated lymphocytes was approximately 85% after 24 h as compared to less than 25% in stimulated cells.

Blockade of a cardiac K+ channel by tacrine: interactions with muscarinic and adenosine receptors

The centrally acting anticholinesterase drug tacrine has been shown to block K+ channels in guinea pig left atrium. It competitively blocks the negative inotropic effects of adenosine, 2-chloroadenosine and carbachol. Ka values obtained from dose ratio plots were 2.5, 3.5 and 2.9 microM respectively. It was also able to antagonize the shortening of the action potential due to these compounds. Doses of tacrine ranging from 1 to 4 microM restored the AP configuration close to control values. Tacrine also antagonized the binding of 1-quinuclidinyl[phenyl-4-3H]benzilate ([3H]QNB) to membranes derived from the atrium and cerebral cortex. Ki values of 1.8 +/- 0.33 and 1.3 +/- 0.47 microM were obtained respectively. Tacrine was a weak competitor of [3H]phenylisopropyladenosine ([3H]L-PIA) binding in brain membranes. Its diverse pharmacological effects may be relevant to its use in Alzheimer's disease.

Photorepair of ultraviolet radiation-induced pyrimidine dimers in corneal DNA

The induction and photorepair of pyrimidine dimers in DNA have been measured in the ultraviolet-irradiated, corneal epithelium of the marsupial, Monodelphis domestica, using damage-specific nucleases from Micrococcus luteus in conjunction with agarose gel electrophoresis. We observed that FS-40 sunlamps (280-400 nm) induced 7.2 +/- 1.0 X 10(-5) pyrimidine dimers per kilobase (kb) of DNA per J/m2. Following 100 J/m2, 50% and greater than 90% of the dimers were photorepaired during a 10- and 30-min exposure to photoreactivating light (320-400 nm), respectively. In addition, approximately 70% and approximately 60% of the dimers induced by 300 and 500 J/m2, respectively, were repaired by a 60-min exposure to photoreactivating light. The capacity of the corneal epithelium of M. domestica to photorepair pyrimidine dimers identifies this animal as a potentially useful model with which to determine whether pyrimidine dimers are involved in pathological changes of the irradiated eye.

Variations in excision repair of UVB-induced pyrimidine dimers in DNA of human skin in situ

The excision repair kinetics of UVB (280-320 nm)*-induced pyrimidine dimers in DNA of human skin in situ was determined for seventeen volunteers using a dimer-specific endonuclease from Micrococcus luteus in conjunction with agarose gel electrophoresis. Removal of pyrimidine dimers from human skin could be detected within 6 h after irradiation and the average half-life for removal of pyrimidine dimers was 11.0 h (+/- 4.3 h). However, there was significant inter-individual variability of repair as indicated by a half-life coefficient of variation of 38%.

Evaluation of densitometry data using interactive computer graphics: application to DNA agarose gels

A method of analyzing DNA agarose gels using interactive computer graphics is described. After electrophoresis in an alkaline agarose gel, DNA is neutralized, stained with ethidium bromide and excited with ultraviolet radiation. The resulting fluorescent distribution on the gel is photographed, and the negative scanned by a digitizing densitometer. The data is subsequently analyzed using a computer program developed to facilitate manipulation and selection of data from the densitometer trace. The method has been applied to determine pyrimidine dimer yields in DNA from human lymphocytes exposed to UV radiation. The technique significantly reduces the time required to analyze such data, while also providing greater accuracy. The method could be easily adapted to assist in similar analyses of other macromolecules such as RNA or proteins.

Effects of guanyl nucleotides on the activation of cardiac muscarinic receptors

Effects of guanyl nucleotides on the affinity of cholinergic agonists at the [3H]quinuclidinylbenzilate binding site have been compared with their effects on the intact left atrium. The binding of carbachol was described by a two-site model; guanyl nucleotides had little effect on the affinity at either site but increased substantially the proportion of low affinity sites. The negative inotropic effect of acetylcholine (ACh) was unaffected by exogenous guanyl nucleotides or variation in external Mg++ or Ca++. ACh (2 microM) shortened the action potential, reduced spike amplitude and usually increased the maximum diastolic potential. GTP and guanyl-5'-yl-imidodiphosphate in the presence of ACh increased action potential amplitude and duration and increased further the diastolic potential. Low external Mg++ had similar effects to guanyl-5'-yl-imidodiphosphate but their effects were not additive. It is suggested that these compounds delay the activation of a transient outward K+ current by ACh.

Production of pyrimidine dimers in DNA of human skin exposed in situ to UVA radiation

Cyclobutyl pyrimidine dimers, measured as sites recognized by the dimer-specific ultraviolet (UV) endonuclease from Micrococcus luteus, were produced in DNA of human skin exposed in situ to UVA (320-400 nm) radiation. The dimer yields produced by a broadband UVA source, by broadband UVA filtered to remove all light of wavelength less than 340 nm, and by narrow band radiation centered at 365 nm were similar, indicating that UVA radiation, and not stray shorter wavelength radiation, was responsible for dimer production. The identity of the UVA-induced DNA lesions was confirmed as pyrimidine dimers by photoreactivation of approximately 100% of the endonuclease-sensitive sites in vitro with the 40,000 dalton Escherichia coli photoreactivating enzyme.

Quantitation of radiation-, chemical-, or enzyme-induced single strand breaks in nonradioactive DNA by alkaline gel electrophoresis: application to pyrimidine dimers

We have developed an alkaline agarose gel method for quantitating single strand breaks in nanogram quantities of nonradioactive DNA. After electrophoresis together with molecular length standards, the DNA is neutralized, stained with ethidium bromide, photographed, and the density profiles recorded with a computer controlled scanner. The median lengths, number average molecular lengths, and length average molecular lengths of the DNAs can be computed by using the mobilities of the molecular length standards. The frequency of single strand breaks can then be determined by comparison of the corresponding average molecular lengths of DNAs treated and not treated with single strand break-inducing agents (radiation, chemicals, or lesion-specific endonuclease). Single strand break yields (induced at pyrimidine dimer sites in uv-irradiated human fibroblasts DNA by the dimer-specific endonuclease from Micrococcus luteus) from our method agree with values obtained for the same DNAs from alkaline sucrose gradient analysis. The method has been used to determine pyrimidine dimer yields in DNA from biopsies of human skin irradiated in situ. It will be especially useful in determining the frequency of single strand breaks (or lesions convertible to single strand breaks by specific cleaving reagents or enzymes) in small quantities of DNA from cells or tissues not amenable to radioactive labeling.

Modification of the effects of muscarinic agonists by reversible and irreversible anticholinesterase compounds in the guinea pig atrium

The cholinergic agonists acetylcholine (ACh), carbamylcholine and methacholine were found to be equieffective in reducing the force of left atrial contraction, but to differ in their ability to shorten the action potential duration. The irreversible cholinesterase inhibitor soman had no effect on the actions of the non-hydrolyzable agonist carbamylcholine, but potentiated the actions of ACh. The reversible inhibitor edrophonium both potentiated and antagonized the effects of ACh. It antagonized the effects of carbamylcholine and after atrial cholinesterase was inhibited with soman it also antagonized the effects of ACh. Its anticholinesterase action and inhibitory action at the muscarinic receptor were confirmed in separate studies. Edrophonium is approximately 12 times more potent as an anticholinesterase than it is in blocking the muscarinic receptor. However, some actions of edrophonium cannot be explained in the context of its anticholinergic and antiesterase actions. Thus it increases the force of atrial contraction and antagonizes the negative inotropy due to soman. An inhibitory effect on an outward K+ current may be involved. The difference in the ability of the three cholinergic agonists to shorten the action potential may also be related to differences in efficacy at this K+ channel.

Methylation of critical carboxyl groups in the vicinity of the sodium channel of guinea-pig atrium

Methylation of a critical carboxyl group in guinea-pig left atrium with trimethoxonium ion leads to loss of excitability. The critical group(s) could be protected with a number of cationic drugs, so that on washout of the protecting drug and reaction products full excitability returned. Tetrodotoxin, edrophonium, cholinergic agonists and amantadine protected the preparation. During the recovery period readmission of these drugs led to the same pharmacological response as during the control period, suggesting protection of specific site(s). This thesis was confirmed in crossover experiments, in which the atrium was exposed to the methylating agent in the presence of one protecting drug, then exposed to another during recovery. The expected pharmacological responses were obtained. Assay of muscarinic receptors with [3H]-quinuclidinyl benzilate after methylation without protection or in the presence of tetrodotoxin or acetylcholine suggested that these receptors are not involved in the maintenance of excitability. It is postulated that the Na+ channel and the K+ channel are located in the same macromolecular membrane complex, and that the K+ channel has a cholinoreceptive sub-site.

Higher pyrimidine dimer yields in skin of normal humans with higher UVB sensitivity

We have measured UVB (280-320 nm)-induced DNA damage in skin of individuals with different sensitivities to UVB irradiation as measured by minimal erythema dose (MED). The DNA damage was susceptible to cleavage by Micrococcus luteus UV endonuclease, which recognizes pyrimidine dimers in DNA. An alkaline agarose gel electrophoresis method was used to quantitate the number of M. luteus UV endonuclease-sensitive sites in nonradioactive DNA from skin biopsies of 7 individuals irradiated with UVB (0-180 mJ X cm-2). The production of sites correlated well with MED (correlation coefficient = 0.78). The slope of the dose response curve for the most UVB-sensitive individual (MED = 24 mJ X cm-2) and for the least UVB-sensitive individual (MED = 146 mJ X cm-2) were 11.5 X 10(-4) and 2.6 X 10(-4) sites per 1000 bases per mJ X cm-2, respectively. The UVB-induced DNA damage was determined to be pyrimidine dimers by its susceptibility to cleavage by M. luteus UV endonuclease and its photoreactivability by Escherichia coli photoreactivating enzyme.

Serum effects on DNA repair in human cells

Freshly isolated human lymphocytes were used to determine how serum supplements affect cellular capacity to repair UV damage. Repair capacity was always found to be greatest in medium supplemented with autologous plasma. Variability in repair capacity among individuals was greater in serum supplemented medium than in unsupplemented medium. Thus, in vitro cellular responses will most accurately represent in vivo responses if autologous serum factors are present in the culture medium. This is of particular importance in studies attempting to correlate DNA repair capacity with age or susceptibility to carcinogenesis.

Interactions of amantadine with the cardiac muscarinic receptor

The antiviral drug amantadine has anticholinergic effects in the guinea-pig atrium at concentrations greater than 1 X 10(-4)M. It is a competitive inhibitor of [3H]-quinuclidinyl benzilate binding to the muscarinic receptor, but antagonizes the negative inotropic effect of acetylcholine in a non-competitive manner. It increases the duration of the atrial action potential and also increases the force of atrial contraction. These effects are evident at approximately 10 times lower concentrations than the antimuscarinic effects. The increase in contractility can be reversed by propranolol (5 X 10(-7)M) but the increase in action potential duration is potentiated by propranolol. Shortening of the action potential duration by acetylcholine was reversed by amantadine, but at approximately ten times lower levels than were needed to reduce the negative inotropic effect. Interactions between beta adrenoceptor binding of [3H]-dihydroalprenolol and amantadine could not be demonstrated. Similarly, binding of [3H]-nitrendipine to the calcium channel is not influenced. It is suggested that amantadine may exert its positive inotropic effect by interaction with the potassium channel, causing a delay in outward current.

Effect of tetrodotoxin on the inward ionic current of the guinea pig atrium

The inward ionic current in the atrium has been measured by electronic differentiation of the voltage, time signal, on the assumption that the single cell penetrated by the micro-electrode shows cable-like properties. The method exploits fully information contained in the upstroke of the action potential, and an internally consistent set of parameters can be derived. Tetrodotoxin was found to reduce the fast inward ionic current, and to shift the voltage of maximum current flow to more negative values. TTX augmented the effects of high stimulation rates but did not alter the refractory period of the atrium. It is suggested that TTX interacts with the Na+ channel so as to reduce activation of the Na+ current and hence unit conductance. The present results are consistent with the apparent voltage-dependence of TTX action, since activation and inactivation of the Na+ current are both voltage-sensitive phenomena.

Inhibition of unscheduled DNA synthesis in human lymphocytes by chemical carcinogens

Freshly isolated human peripheral lymphocytes were treated with an alkylating agent immediately after collection and subsequently treated with UV radiation. This system was used because it represents a method for assaying damage in cells immediately after their removal from the host. The amount of UV-induced repair was measured as unscheduled DNA synthesis (UDS) by incorporation of [3H]deoxythymidine into the cellular DNA. The alkylating agents beta-propiolactone (BPL) and methyl methane-sulfonate (MMS) inhibited UDS at concentrations of 0.08 mM and 0.6 mM, respectively. Lower concentrations had no effect. Lymphocytes allowed to remain in culture medium after treatment with the alkylating agents did not recover the ability to perform UV-induced UDS even when cells were irradiated 48 h after carcinogen treatment. The decrease in UV-induced UDS resulting from alkylating agent treatment could not be attributed to cell death.

Fine-structure studies of experimental skeletal muscle trauma

A study was made of damage to skeletal muscle caused by a high-velocity rifle bullet. Such damage extends peripherally from the permanent wound cavity and is focal in nature. A fine-structure investigation of this region suggests that some components of the muscle are more susceptible to the wounding process than others. The sarcoplasmic reticulum appeared most sensitive and areas as far as 3 cm from the wound cavity frequently showed gross vacuolization. Mitochrondrial damage was seen, but only in areas where there was also damage to myofibrils and the microvasculature. Focal capillary leakage up to 3 cm from the wound cavity was demonstrated in an earlier study by the use of a fluorescein-labelled dextran (Paddle and Freeman, 1979). This finding was confirmed. A possible correlate at the fine structural level was swelling of te capillary endothelial cells, which occurred in the absence of other signs of microvascular damage. Damage to the endothelial junctions was not observed, even in severely damaged tissue. Intravascular colloidal carbon escaped into the extravascular space only when the microvasculature was fractured. The relationship of these findings to macroscopic damage is discussed.

Cholinergic mechanisms in heart: interactions with 4-aminopyridine

Acetylcholine (ACh) hyperpolarized the guinea-pig atrium and increased the maximum rate of rise of the spike and ionic conductance. There was a dose-dependent decrease in action potential duration in most preparations. However, some atrial showed a contractility decrease without a concomitant change in action potential duration. This was not related to acetylcholinesterase activity. Reduction in contractility by ACh resulted from doses 10 times lower than were required for action potential shortening. Small quantitative differences in electrical response were seen between the left and right atria. 4-Aminopyridine lengthened the action potential and increased spike amplitude. These effects were not frequency-dependent but were potentiated by low Ko+. This drug antagonized both the electrical and contractile effects of ACh, suggesting that they are mediated by an increase in KO+ permeability. Modification of excitation-contraction coupling by ACh is discussed and a role for cyclic guanosine 3':5'-monophosphate suggested.

The effects of l-propranolol and practolol on atrial and nodal transmembrane potentials

Effects of l-propranolol, racemic propranolol and practolol have been determined on transmembrane potentials recorded in guinea-pig left atrium and in sinoatrial and atrioventricular nodes of the rabbit heart. In addition to the voltage -time recording of the action potential, its first time derivative was displayed as a function of membrane voltage, forming a phase-plane trajectory. A number of parameters of the action potential were determined from this trajectory. At the concentrations used the beta adrenoceptor blocking agents reduced the maximum rate of rise of the atrial action potential and slowed repolarization. The velocity of the propagated spike was reduced, and the maximum ionic conductance was also reduced. The excitation potential of the propagated spike was unaffected. The membrane effects were markedly dependent on the frequency of stimulation. The beta adrenoceptor blocking agents were without effect on either the sinoatrial or atrioventricular nodes. Since the spontaneously active right atrium beats more slowly than the heart of the intact rabbit, the atrioventricular node was electrically stimulated at 5 to 6 Hz. Neither drug affected the ability of the node to follow these stimulation frequencies. The importance of these effects in the control of cardiac arrhythmias is discussed.