Acute or chronic exercise alters angiotensin II-induced contraction of rat aorta

Chronic exercise substantially shifted the dose-response curve for angiotensin II (ANG II)-induced contractions to the right with increases in the EC50 value in both endothelium-intact and endothelium-denuded aortae. An acute endurance exercise also caused a 3-fold increase in the EC50 value in both endothelium-intact and endothelium-denuded aortae from sedentary control rats. Whereas, no substantial increase in the EC50 value was observed in trained rats after an acute endurance exercise. Thus, chronic exercise attenuates ANG II receptor-mediated contraction of rat aortae. An acute exercise also caused the reduced responses to ANG II in sedentary control rats but not in chronically exercise-trained rats.

Direct evidence for the occurrence of superoxide radicals in the small intestine of the burned rat

To determine if superoxide radicals (O2-) and related metabolites are generated in extradermal tissues of burned animals, 2-methyl-6-[p-methoxyphenyl]-3,7-dihydroimidazol [1,2-å]pyrazin-3-one (MCLA) was infused intravenously into rats, and change in the chemiluminescence (CL) intensity of the small intestine was determined by using a sensitive photodetector. When animals were challenged with burn stress of 40% total body surface area (TBSA), the CL intensity of the intestine gradually increased, reaching a maximum within 1 hour and remaining elevated for up to 3 hours. Pretreatment of animals with a long-acting superoxide dismutase (SOD) derivative (SM-SOD) significantly inhibited the increase in CL intensity. Administration of SM-SOD immediately after inducing burn injury also significantly inhibited the increase in CL. These results suggest that superoxide radicals are generated in extradermal tissues, such as the small intestine, in the early stage after burn injury.

Mechanism of activation of nonselective cation channels by putative M4 muscarinic receptor in guinea-pig chromaffin cells

1. Mechanisms involved in the generation of nonselective cation currents (INS) by muscarinic agonists in the chromaffin cell were investigated by the perforated patch method. 2. Bath application of muscarine (0.1-30 microM) produced an inward INS with or without a transient outward current at -40 mV, whereas oxotremorine (0.06-60 microM) induced INS alone. Rectangular hyperbolas with EC50s of 2.01 and 0.21 microM were fitted to muscarine- and oxotremorine-induced INSS, respectively, and the maximal amplitude of the former was about 3.4 times larger than that of the latter. 3. In 36% of the cells exposed to Ca(2+)-free solution, muscarine INS was suppressed, being 53% of control 20 min after the perfusion, and in four cells that were incubated with Ca(2+)-free solution for 2 h or more, the INS averaged 44% of that induced subsequently in normal solution. In contrast, muscarine INS was enhanced by about 30% when A-23187 was added to normal solution. 4. W-7 and W-5, calmodulin-related agents, were almost equally potent in inhibiting muscarine INS, whereas compound 5, a potent inhibitor of calmodulin-dependent kinase II (CaM kinase II), produced no evident inhibition. 5. HA1004, a weak kinase C inhibitor, induced a reversible suppression of muscarine INS with an IC50 of 163 microM, whereas H-8, another kinase inhibitor, produced an even small degree of inhibition. Administration of phorbol 12, 13-dibutyrate did not mimic muscarinic stimulation of NS channels; rather, it led to a progressive inhibition of INS and this inhibition was almost complete within 20 min. An inactive phorbol ester had no such effect. 6. The muscarinic antagonists, pirenzepine and AF-DX 116, shifted the dose-response curve for the muscarine INs to the right in a parallel manner. The KDS for pirenzepine and AF-DX 116 were estimated to be 13 nM (95% confidence interval, 11-16 nM) and 365 nM (283-470 nM), respectively.7. These results suggest that muscarine efficiently produces INS, probably through binding to the M4 subtype, that intracellular Ca2+ has a facilitating, but not an essential role in the generation of INs, and that neither CaM kinase II nor protein kinase C is involved.

Subsite-specific risk factors for colorectal cancer: a hospital-based case-control study in Japan

To investigate the subsite-specific risk factors for colorectal cancer, we conducted a case-control study, using a common questionnaire which inquired about general lifestyles over the past five years (1988-92), at the Aichi Cancer Center Hospital, Nagoya, Japan. This study compared 432 patients with histopathologically diagnosed colorectal cancer (94 proximal colon [cecum, ascending colon, transverse colon]; 137 distal colon [descending colon, sigmoid colon]; 201 rectum [rectosigmoid, rectum]); and 31,782 first-visit outpatient controls who were free from cancer. In both genders, habitual smoking selectively increased the risk for rectum cancer. Soft or loose feces increased the risk for all subsites of colorectal cancer, particularly in female rectum cancer (odds ratio [OR] = 4.5). Among female dietary habits, Japanese-style foods decreased the risk for distal colon cancer, but increased the risk for proximal colon cancer. These results suggested that the risk factors for colorectal cancer differ by subsite among such a low-risk population as the Japanese. It is suggested also that 'irritable bowel' (soft or loose feces) might be associated with distal subsites of colorectal cancer, independently or combined with habitual smoking.

Structure of ascidiacyclamide as the ethanol water solvate, a cytotoxic cyclic peptide from Ascidian

The X-ray crystal structure determination of the C2H5OH.H2O solvate of ascidiacyclamide (C36H52N8O6S2), a cytotoxic cyclic peptide from marine tunicate Ascidian, revealed a C2-symmetric saddle-shaped rectangular conformation of the molecule. The water and ethanol molecules are located on the crystallographic diad axis and are held by hydrogen bonds and van der Waals contacts with the polar ring N atoms and nonpolar D-Val side-chain atoms, respectively. The molecular conformation and the interaction with solvent molecules are nearly the same as those of the compound with C2H5OH.2H2O [Ishida, In, Doi, Inoue, Hamada & Shioiri (1992). Biopolymers, 32, 131-143].

Effect of adrenomedullin on hepatic pericytes (stellate cells) of the rat

When hepatic stellate cells (Ito cells, fat-storing cells) were incubated with adrenomedullin, they underwent relaxation as monitored by the silicone-rubber membrane method; 43%, 65% and 87% of stellate cells relaxed 5, 10 and 20 min, respectively, after addition of 10(-6) M adrenomedullin. Adrenomedullin also triggered the dissociation of F-actin and induced transformation of stellate cells to dendritic cell-like structure. When incubated with 10(-6) M of adrenomedullin for 30 min, cellular levels of cAMP increased from the basal value of 10.2 +/- 1.4 to 107 +/- 2.8 pmol/2 x 10(5) cells without affecting cGMP levels. The reaction occurred dose-dependently and was inhibited by an antagonist of calcitonin gene-related peptide. Adrenomedullin had negligible effects on DNA and protein synthesis in proliferating stellate cells. Thus, adrenomedullin is a potent relaxing peptide to hepatic stellate cells and may contribute to the regulation of sinusoidal microcirculation.

Evidence for deactivation of both ectosolic and cytosolic 5'-nucleotidase by adenosine A1 receptor activation in the rat cardiomyocytes

Adenosine, an important regulator of many cardiac functions, is produced by ectosolic and cytosolic 5'-nucleotidase. The activity of these enzymes is influenced by several ischemia-sensitive metabolic factors, e.g., ATP, ADP, H+, and inorganic phosphate. However, there is no clear evidence that adenosine itself affects 5'-nucleotidase activity. This study tested whether adenosine decreases the activity of ectosolic and cytosolic 5'-nucleotidase. Cardiomyocytes were isolated from adult male Wistar rats and suspended in the modified Hepes-Tyrode buffer solution. After stabilization, isolated cardiomyocytes were incubated with and without adenosine (10(-9) - 10(-4) M). Ectosolic and cytosolic 5'-nucleotidase activity was decreased by exogenous adenosine (ectosolic 5'-nucleotidase activity, 20.6 +/- 2.3 vs. 8.6 +/- 1.6 mumol/min per 10(6) cells [P < 0.05]; cytosolic 5'-nucleotidase activity, 2.47 +/- 0.58 vs. 1.61 +/- 0.54 mumol/min per 10(6) cells [P < 0.05] at 10(-6) M adenosine) after 30 min. The decrease in ectosolic and cytosolic 5'-nucleotidase activity was inhibited by 8-phenyltheophylline and pertussis toxin, and was mimicked by N6-cyclohexyladenosine, an adenosine A1 receptor agonist. Neither CGS21680C, and A2 receptor agonist, nor cycloheximide deactivated ectosolic and cytosolic 5'-nucleotidase. Thus, we conclude that activation of adenosine A1 receptors is coupled to Gi proteins and attenuates ectosolic and cytosolic 5'-nucleotidase activity in rat cardiomyocytes.

Characteristic molecular packing in the crystal structure of tert-butoxycarbonyl-L-phenylalanyl-L-methionine methyl ester

The molecular conformation and association of the peptide Boc-L-Phe-L-Met-OMe have been studied in the solid state by X-ray diffraction. The peptide crystallizes in the orthorhombic system, space group P2(1)2(1)2(1), with cell parameters of a = 9.821(2), b = 25.394(6), c = 28.714(8) A, V = 7161(3) A3. The structure has been solved by direct methods and refined to a final R of 0.079 for 5464 independent reflections with Fo > or = sigma(Fo). The crystal consists of three independent molecular conformations per asymmetric unit. Respective peptide backbones adopt an extended conformation with the side-chains of Phe and Met residues being arranged below and above the backbone chains. Contrary to the sheet structure most frequently observed in the crystal packing of the extended peptide conformations, three independent molecules lie spirally along the c-axis and form a pin-wheel-like crystal packing. The sheet structures formed by two of three independent molecules are almost at right angles to the backbone of the remaining molecule. This molecular packing mode would provide a possible interaction model between the intersecting beta-sheet structure and single-strand structure of polypeptide.

Alteration of the p53 tumor suppressor gene occurs independently of K-ras activation and more frequently in serous adenocarcinomas than in other common epithelial tumors of the human ovary

To clarify the role of the p53 tumor suppressor gene in the development of human ovarian epithelial tumors and to study the association of p53 alterations with K-ras activation, a series of 70 common epithelial ovarian tumors from Japanese patients was studied. These included 31 serous adenocarcinomas, 12 mucinous adenocarcinomas, 5 mucinous tumors of borderline malignancy, 13 endometrioid adenocarcinomas, and 9 clear cell carcinomas. Allelic loss, recognized at the polymorphic site in codon 72 of the p53 gene, was detected in 14 of 36 (39%) informative cases by restriction fragment length polymorphism analysis and by single-strand conformation polymorphism (SSCP) analysis of polymerase chain reaction (PCR)-amplified DNA fragments. Mutations in the highly conserved regions of the p53 gene were detected by SSCP analysis of PCR-amplified fragments. Mutations were found in 22 of 70 (31%) ovarian tumors, including 1 of 5 mucinous tumors of borderline malignancy. Mutations were subsequently characterized by direct sequencing. Single missense base substitutions were detected in 13 ovarian carcinomas and in one case of mucinous tumor of borderline malignancy. Short (1-8 bp) deletions and insertions were found in 8 cases. Mutations in the p53 gene occurred more frequently in serous adenocarcinomas (14/31, 45%) than in all nonserous types of malignant epithelial tumors combined (7/34, 21%; P = 0.032). Point mutations in K-ras were identified by dot blot hybridization analysis of PCR-amplified fragments with mutation-specific oligonucleotides and by direct sequencing. The overall frequency of K-ras mutations was 19/70 (27%). K-ras mutations were found in 12 of 17 (71%) mucinous tumors (8/12 mucinous carcinomas [67%] and 4/5 mucinous tumors of borderline malignancy [80%]), and occurred more frequently than in serous carcinomas (4/31, 13%; P = 0.00009) or in all nonmucinous types of ovarian epithelial tumors combined (7/53, 13%; P = 0.00002). These data suggest that different combinations of oncogenes and/or tumor suppressor genes may be involved in the genesis and development of histologically distinct categories of common epithelial tumors of the human ovary.

Variant forms of glucokinase gene in Japanese patients with late-onset type 2 diabetes

We have applied the technique of single-strand conformation polymorphism analysis to detect mutations of the glucokinase gene in 50 Japanese patients with late-onset type 2 diabetes and in 50 normal Japanese subjects. Out of the 50 patients with late-onset type 2 diabetes, we observed three kinds of variant patterns: one in exon 1b, one in exon 4, and one in exon 5. The incidence of these patterns was one in exon 1b, two in exon 4 and one in exon 5. Direct sequencing of exon 1b and exon 5 revealed mutations in intron areas at the 12th nucleotide downstream from the 5' splice points in two cases. Direct sequencing of exon 4 revealed a heterozygous silent mutation, CCC[Pro]-->CCG[Pro] at codon 145. In contrast, 50 normal Japanese subjects showed no variant patterns in any exons. Our results showed that although 8% (4 out of 50) of Japanese patients with late-onset type 2 diabetes have variant forms of the glucokinase gene, none is expected to cause apparent qualitative changes in glucokinase. We think that the frequency of mutations of the glucokinase gene which could cause qualitative change is very low in Japanese patients with late-onset type 2 diabetes.

Multiple pulmonary hamartomas: report of a case

Among lung tumors, multiple hamartomas are uncommon while multiple chondromatous hamartomas are extremely rare, with only 12 cases having been previously reported. A case of multiple pulmonary chondromatous hamartomas in a 58-year-old Japanese man who has been followed up for 28 years is herein presented.

Analysis of clonality by amplification of short tandem repeats. Carcinomas of the female reproductive tract

The clonal composition of cancers of the female reproductive tract was evaluated by analysis of patterns of X-chromosome inactivation. Using DNA extracted from frozen tissues or paraffin-embedded archival specimens as template, polymerase chain reaction (PCR) was performed to generate amplified DNA fragments of exon 1 of the X-linked androgen receptor gene, which contains a highly polymorphic trinucleotide repeat. Predigestion of tumor DNA with methylation-sensitive restriction endonuclease Hha I or Hpa II permitted selective PCR amplification from the methylated (uncleaved) allele. Of a total of 54 tumors analyzed, 50 cases showed heterozygosity (93%) and were therefore informative for clonal analysis. Monoclonal composition of the tumors was suggested in a total of 49 of 50 cases, including 12 adenocarcinomas of the uterine endometrium, 13 squamous cell carcinomas of the uterine cervix, 6 adenocarcinomas of the uterine endocervix, and 18 epithelial tumors of the ovary. However, polyclonal composition was observed in one mucinous carcinoma of the ovary, in which we previously showed that both GGT-->GAT and GGT-->GTT mutations are present in > 20% of total K-ras copies in the tissue. Our studies demonstrate the utility of PCR amplification of highly polymorphic repetitive sequences for analysis of patterns of X-chromosome inactivation. This approach is practical for the analysis of clonal cell composition in a high proportion of both formalin-fixed and frozen archival tissues.

Effect of successful angioplasty following thrombolysis on infarct size and left ventricular function

The role of the angioplasty following thrombolysis in acute myocardial infarction has been discussed in several studies, however the effect of successful angioplasty on infarct size and left ventricular function has not been properly evaluated. Successful reperfusion was achieved in 79 out of 104 patients with primary anterior acute myocardial infarction. These patients were classified as follows, according to the type of intervention during the acute phase: 50 patients in which thrombolysis was successful (the thrombolysis group); 12 patients who underwent successful immediate angioplasty following successful thrombolysis (the immediate angioplasty group); and 17 patients in which rescue angioplasty was successful (the rescue angioplasty group). The 25 patients whose infarct-related vessels were not reperfused after intervention were classified as the non-reperfused group. Infarct size, evaluated as defect volume by T1-201 SPECT, 1 month after the onset, was 840 +/- 154 units (mean +/- S.D.) in the immediate angioplasty group and was similar to that in the thrombolysis group (948 +/- 88 units), but significantly smaller than in the non-reperfused group (1759 +/- 108 units). There were no significant differences in left ventricular function in the immediate angioplasty group and the thrombolysis group. Successful rescue angioplasty did not have any beneficial effect on left ventricular functions or infarct size, when compared with the failed thrombolytic group (1105 +/- 169 units vs. 1617 +/- 169 units). End-diastolic volume (52 +/- 3 ml/m2) in the successful rescue angioplasty group, however, was significantly smaller than in the failed thrombolysis group (67 +/- 3 ml/m2).(ABSTRACT TRUNCATED AT 250 WORDS)

The role of GABA in the central regulation of AVP and ANP release and blood pressure due to angiotensin and carbachol, and central GABA release due to blood pressure changes

To assess whether GABA given intracerebroventricularly (i.c.v.) affects vasopressin (AVP) and atrial natriuretic peptide (ANP) release and changes in blood pressure in response to i.c.v. angiotensin (AT II) and carbachol (CB), or whether changes in blood pressure affect GABA release in the brain, experiments were carried out. In experiment I (Ex I), GABA (100 micrograms) with AT II (50 ng) or CB (25 ng) was i.c.v. administered in conscious rats (n = 12). The same dose of AT II or CB alone also was administered without GABA (n = 12). In experiment II (Ex II), AT II (100 ng/kg per min) or nitropuruside (NP, 10 micrograms/kg per min) was intravenously (i.v.) infused and GABA release in the area adjacent to the paraventricular nucleus was determined, using the microdialysis method, in conscious rats (n = 12). In the experiments, mean arterial blood pressure (MABP), heart rate (HR), plasma AVP and/or ANP and plasma Na+ and K+ levels were measured. In Ex I, i.c.v. AT II increased plasma AVP and MABP without changes in HR and plasma ANP, but i.c.v. GABA never affected these responses. Icv CB also increased plasma AVP and MABP with decreased HR, but did not affect plasma ANP. Icv GABA abolished bradycardiac responses, but did not affect the others. In Ex II, the pressor response to i.v. AT II increased GABA release without apparent decreases in plasma AVP. However, the depressor response to NP produced decreases in GABA release with increased plasma AVP. These results shows that i.c.v. GABA did not affect AVP and pressor responses to i.c.v. AT II and CB, but changes in blood pressure modulates GABA release in the brain with changes in plasma AVP.

Presence of membrane-bound proteinases that preferentially degrade oxidatively damaged erythrocyte membrane proteins as secondary antioxidant defense

Human erythrocytes were oxidized with xanthine/xanthine oxidase/ferric ion or ADP/ferric ion at 37 degrees C for several hours. Band 3 protein and spectrin of the oxidized cells were found to be significantly modified as analyzed by radiolabeling with tritiated borohydride. Sodium dodecylsulfate-polyacrylamide gel electrophoresis of the xanthine/xanthine oxidase/ferric iron-oxidized cells and subsequent immunoblotting with anti band 3 protein showed that band 3 protein was fragmented into smaller molecular-weight fragments. When the cell membrane obtained from the oxidized cells were incubated at pH 7.4 and 37 degrees C for several hours in the presence of alpha-tocopherol, extensive degradation of band 3 protein and spectrin was observed. Band 3 protein was found to be most susceptible to the degradation. Degradation of band 3 protein was also observed after similar incubation of the membrane from the ADP/ferric ion-oxidized cells. Membrane-bound serine- and metalloproteinases were responsible for the degradation of band 3 protein, because the degradation was remarkably inhibited by diisopropyl fluorophosphate and phenylmethylsulfonyl fluoride, and partially by ethylenediaminetetraacetic acid. Hence, the membrane proteins became susceptible to membrane-bound proteinases by oxidative stress. This observation suggests that these membrane-bound proteinases exist to remove oxidatively damaged proteins from the cell membrane.

DNA-binding characterization of a novel anti-tumour benzo[a]phenazine derivative NC-182: spectroscopic and viscometric studies

NC-182 is a novel anti-tumour compound having a benzo[a]phenazine ring. Fluorescence, absorption and c.d. spectroscopy, as well as viscometric titrations, were systematically performed to investigate the interaction mode of this drug with DNA and its effect on DNA conformation, based on comparative measurements with distamycin (DNA minor-groove binder) and daunomycin (DNA-base intercalator). NC-182 was found to be a potent intercalator of DNA, especially the B-form DNA, although no specificity was observed against the base-pair. The binding of NC-182 to B-DNA behaves biphasically, depending on the molar ratio (r) of drug to DNA: NC-182 acts to render the B-form structure rigid at relatively low r value and to promote the transformation of B- to non-B forms at high r values. It was also shown that NC-182 promotes the unwinding of Z-form DNA to B-form. Viscometric, u.v. 'melting' and c.d. experiments further showed that (1) the DNA duplex structure is thermally stabilized by intercalation with NC-182 and (2) the intercalation of NC-182 into a poly(dA).2poly(dT) DNA structure thermally stabilizes the triplex structure, resulting in a melting point close to that of the duplex structure; the melting curves of triplex and duplex structures coincide at r > 0.06. These observations make a significant contribution to our understanding of the biological properties of this novel benzo[a]phenazine derivative, a new anti-tumour tumour agent against multidrug-resistant and sensitive tumours.

Vagally mediated heart rate recovery after exercise is accelerated in athletes but blunted in patients with chronic heart failure

OBJECTIVES

Vagally mediated heart rate recovery after exercise was assessed in patients with chronic heart failure and in well trained athletes by analyzing the postexercise heart rate decay.

BACKGROUND

Vagal reactivation is an important cardiac deceleration mechanism after exercise. However, alterations of this mechanism under pathologic conditions have not been characterized because of the lack of a specific index.

METHODS

To find a vagally mediated component of heart rate recovery, the time constants of the beat-by-beat heart rate decay for the first 30 s (T30) and the first 120 s (T120) after exercise were obtained at six levels of exercise in eight normal volunteers: 1) at maximal exercise, 2) at anaerobic threshold, 3) at anaerobic threshold with propranolol administration, 4) at anaerobic threshold with atropine administration, 5) at anaerobic threshold with concomitant administration of both drugs, and 6) at 50% of anaerobic threshold. To investigate the effects of heart failure and endurance training on vagally mediated heart rate recovery, T30 and T120 at anaerobic threshold were obtained in 20 patients with chronic heart failure and in 9 cross-country skiers.

RESULTS

In normal volunteers, T30 and T120 were markedly prolonged by atropine administration, indicating that both time constants are mediated by vagal reactivation. Moreover, T30 was almost independent of the exercise intensity and sympathetic blockade, whereas T120 was affected by sympathetic nerve activity and exercise work load. These results indicate that T30 is mediated primarily by vagal reactivation, independent of sympathetic withdrawal, and is significantly smaller in athletes (p < 0.01) and significantly larger in patients with chronic heart failure (p < 0.01) than that in respective age-matched normal control subjects.

CONCLUSIONS

The T30 value could be a specific index for vagally mediated heart rate recovery. Vagally mediated heart rate recovery after exercise is accelerated in well trained athletes but blunted in patients with chronic heart failure.

Molecular cloning and chromosomal assignment of the mouse C-type natriuretic peptide (CNP) gene (Nppc): comparison with the human CNP gene (NPPC)

The mouse C-type natriuretic peptide (CNP) genomic fragment was isolated from a mouse genomic DNA library. The mouse CNP gene is composed of at least two exons and one intron. The 5'-flanking region contains an array of cis-acting regulatory elements and a dinucleotide CA repeat (microsatellite). Analysis of the deduced amino acid sequences revealed that mouse preproCNP is a 126-amino-acid peptide and that its C-terminal 22-residue peptide preceded by Lys-Lys is identical to porcine, rat, and human CNPs. On the basis of the polymerase chain reaction-analyzed microsatellite length polymorphisms among recombinant inbred strains of mice, the CNP gene (Nppc) was assigned to mouse chromosome 1. Furthermore, the human CNP 5'-flanking region was extended for sequencing, and comparison of the mouse and human CNP genomic sequences revealed regions of conservation and diversity. Using somatic hybrid cell methodology, the CNP gene (NPPC) was assigned to human chromosome 2. The present study has added another locus to the conserved syntenic group in mice and humans.

A comparative ESR study of some paramagnetic materials as probes for the noninvasive measurement of dissolved oxygen in biological systems

The ESR properties of three types of paramagnetic material, active charcoal, fusinite and a stable nitroxide radical 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPONE), were examined in order to evaluate their suitability as probes to measure dissolved intra- and extra-cellular oxygen. Although, with changes in oxygen concentration, a greater change in the linewidth of ESR signals was observed with fusinite or active charcoal, it took a long time (15 min for active charcoal and more than 6 h for fusinite) for equilibrium to be achieved. On the other hand, equilibrium was reached very rapidly in the case of the TEMPONE spectra although the sensitivity to changes in oxygen concentration was only moderate. Furthermore, since lipid bilayers are permeable to TEMPONE, this compound can be used to measure intracellular oxygen concentration when employed in combination with membrane-impermeable spin-broadening reagents which act on ESR signals arising from extracellular probes. A perdeuterated derivative of TEMPONE is useful in that it gives a greater signal-to-noise ratio and greater sensitivity to changes in oxygen concentration. In conclusion, active charcoal is suitable as a probe for extracellular oxygen in a system where changes are slow, while nitroxide is a versatile probe for measuring rapidly changing intra- and extra-cellular oxygen concentrations.