Hydrogen peroxide relaxes porcine coronary arteries by stimulating BKCa channel activity

It has been known for a number of years that neutrophils and macrophages secrete H2O2 while fighting disease, and the levels obtained within the vasculature under these conditions can reach several hundred micromolar. Because the effect of H2O2 on vascular smooth muscle is not fully understood, the present study examined the cellular effects of H2O2 on coronary arteries. Under normal ionic conditions, H2O2 relaxed arteries that were precontracted with prostaglandin F2alpha or histamine (EC50 = 252 +/- 22 microM). The effect of H2O2 was concentration dependent and endothelium independent. In contrast, H2O2 did not relax arteries contracted with 80 mM KCl, suggesting involvement of K+ channels. Single-channel patch-clamp recordings revealed that H2O2 increased the activity of the large-conductance (119 pS), Ca2+- and voltage-activated K+ (BKCa) channel. This response was mimicked by arachidonic acid and inhibited by eicosatriynoic acid, a lipoxygenase blocker, suggesting involvement of leukotrienes. Further studies on intact arteries demonstrated that eicosatriynoic acid not only blocked the vasodilatory response to H2O2 but unmasked a vasoconstrictor effect that was reversed by blocking cyclooxygenase activity with indomethacin. These findings identify a novel effector molecule, the BKCa channel, which appears to mediate the vasodilatory effect of H2O2, and suggest that a single signaling pathway, arachidonic acid metabolism, can mediate the vasodilatory and vasoconstrictor effects of H2O2 and possibly other reactive oxygen species.

Procedures for skin diseases performed by physicians in 1993 and 1994: analysis of data from the National Ambulatory Medical Care Survey

BACKGROUND

The provision of ambulatory dermatologic procedural care is not well characterized.

OBJECTIVE

Our purpose was to determine the frequency that different cutaneous procedures are performed by different physician specialties and the diagnoses corresponding to these procedures.

METHODS

Outpatient dermatologic procedures recorded in the 1993 and 1994 National Ambulatory Medical Care Survey were analyzed. To define dermatologic procedures and diagnoses, the International Classification of Diseases diagnosis and procedure codes were identified that related to the skin and subcutaneous tissues. Sampling weights were applied to achieve the nationally representative estimates.

RESULTS

During 1993 and 1994, an estimated 37 million dermatologic procedures were performed. Most were performed by dermatologists (69%) and by family and general practice physicians (15%). A single procedure, "Other local excision or destruction of lesion or tissue of skin and subcutaneous tissue," constituted 65% of all of the dermatologic procedures. UV light treatments, ambulatory microscopic examination of skin specimens, and acne surgical procedures were performed almost exclusively by dermatologists. Most skin biopsies (82%) and excision/destruction procedures (71%) were performed by dermatologists. Actinic keratoses and viral warts accounted for 25% of all cutaneous dermatologic diagnoses treated.

CONCLUSION

Dermatologists have far more experience performing skin biopsies and excision/destruction procedures than other physicians. Cost containment efforts that deny coverage for treatment of actinic keratoses and viral warts would affect a significant portion of cutaneous procedures.

Growth factor-mediated K+ channel activity associated with human myeloblastic ML-1 cell proliferation

ML-1 cell proliferation is dependent on the presence of serum growth factors. Removing serum from the culture medium results in growth arrest and promotes differentiation. In this study, we found that a 4-aminopyridine-sensitive K+ channel was highly expressed in proliferating ML-1 cells and significantly diminished in G1-arrested ML-1 cells induced by serum deprivation but was restored within 30 min in these cells with addition of 10% fetal bovine serum (FBS) or 5 ng/ml epidermal growth factor (EGF). Intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels, but not guanosine 3',5'-cyclic monophosphate, were significantly increased in serum-deprived cells stimulated by FBS or EGF, and the effects of FBS and EGF on the channel activation were mimicked by exogenous cAMP. In inside-out patches, K+ channel activity was significantly increased by the cAMP-dependent protein kinase catalytic subunit, whereas the effect of EGF on K+ channel activation was blocked by Rp-8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphothioate. Together, our results demonstrate that serum growth factors stimulate K+ channel activity in proliferation of ML-1 cells through protein kinase-induced phosphorylation and suggest an important molecular mechanism for serum growth factor-stimulated mitogenesis in ML-1 cells.

Nitrovasodilators relax mesenteric microvessels by cGMP-induced stimulation of Ca-activated K channels

Nitric oxide (NO) released from endothelial cells or exogenous nitrates is a potent dilator of arterial smooth muscle; however, the molecular mechanisms mediating relaxation to NO in the microcirculation have not been characterized. The present study investigated the relaxant effect of nitrovasodilators on microvessels obtained from the rat mesentery and also employed whole cell and single-channel patch-clamp techniques to identify the molecular target of NO action in myocytes from these vessels. Both sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) relaxed phenylephrine-induced contractions by approximately 80% but were significantly less effective in relaxing contractions induced by 40 mM KCl. Relaxation to SNP was also inhibited by the K(+)-channel blocker tetraethylammonium or by inhibition of the activity of the guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinase (PKG). These results suggest that SNP stimulated K+ efflux by opening K+ channels via PKG-mediated phosphorylation. Perforated-patch experiments revealed that both SNP and SNAP increased outward currents in microvascular myocytes, and single-channel studies identified the high-conductance Ca(2+)- and voltage-activated K+ (BKCa) channel as the target of nitrovasodilator action. The effects of nitrovasodilators on BKCa channels were mimicked by cGMP and inhibited by blocking the activity of PKG. We conclude that stimulation of BKCa-channel activity via cGMP-dependent phosphorylation contributes to the vasodilatory effect of NO on microvessels and that a direct effect of NO on BKCa channels does not play a major role in this process. We propose that this mechanism is important for the therapeutic effect of nitrovasodilators on peripheral resistance and arterial blood pressure.

Estrogen relaxation of coronary artery smooth muscle is mediated by nitric oxide and cGMP

Estrogens are proposed to exert protection against cardiovascular disease, and evidence now suggests that this protection involves a direct vasodilatory effect. We have shown previously that estrogen relaxes endothelium-denuded porcine coronary arteries by opening the large-conductance calcium- and voltage-activated potassium (BKCa) channel of myocytes through guanosine 3',5'-cyclic monophosphate (cGMP)-dependent phosphorylation (35). The present study confirms these results and now demonstrates that this mechanism involves production of nitric oxide (NO). S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, or 8-bromo-cGMP mimicked the effect of estrogen on BKCa channels. Furthermore, inhibition of NO synthase (NOS) attenuated estrogen- or tamoxifen-induced BKCa-channel activity, and this effect was disinhibited by L-arginine. Inhibition of guanylyl cyclase activity blocked the stimulatory effect of estrogen, SNAP, or L-arginine on BKCa channels. Furthermore, 17 beta-estradiol stimulated accumulation of nitrite and cGMP in coronary myocytes. Therefore, we propose that the vasodilatory effect of estrogen on the coronary circulation is mediated by NO. A portion of the beneficial cardiovascular effects of estrogen may be attributed to relaxation of vascular smooth muscle by a process that involves NO- and cGMP-dependent stimulation of BKCa channels.

Therapeutic options and results for the management of minimally invasive carcinoma of the breast: influence of axillary dissection for treatment of T1a and T1b lesions

BACKGROUND

Axillary dissection has maintained a role of primacy for the surgical therapy of invasive carcinoma of the breast for many years. More recently, early (T1) minimally invasive carcinoma of the breast has been diagnosed with increasing frequency, and the necessity of axillary dissection for sampling purposes in these small tumors has been questioned, based primarily on the finding of low rates of axillary metastases.

STUDY DESIGN

The Rhode Island State Tumor Registry records of 1,126 patients with T1a or T1b tumors were examined to assess the effect of axillary dissection on patient outcome. These data span 9 years (1985 to 1992) with a median follow-up duration of 64 months. Five-year overall, disease-free, and breast cancer-specific (determinate) survival were determined according to treatment modality. Axillary node positivity was calculated for patients with minimally invasive carcinoma of the breast who underwent axillary dissection. Multivariate statistical methods were used to provide adjustment for known confounding prognostic variables.

RESULTS

Omission of axillary dissection occurred in 157 cases and correlated with reductions in overall, disease-free, and breast cancer-specific survival (p < .001 in all cases). Nodal status significantly influenced disease-free survival in minimally invasive carcinoma of the breast (90 percent node-negative compared with 76 percent node-positive, p = .02). Nodal positivity was evident in 18.2 percent of patients undergoing axillary dissection for minimally invasive carcinoma of the breast (9.8 percent for T1a, 19.4 percent for T1b, p = .01). In multivariate analysis, the performance of axillary dissection with breast conservation or modified radical mastectomy were independent predictors of overall survival, as well as disease-free and breast cancer-specific survival.

CONCLUSIONS

A significant number of patients with small (less than or equal to 1 cm) invasive tumors of the breast will have axillary metastases at the time of diagnosis. Omission of axillary dissection in these patients was associated with significant impairment of overall, disease-free, and breast cancer-specific survival. Axillary dissection should continue to be a standard approach for the surgical therapy of all patients with invasive carcinoma of the breast, regardless of tumor size.

A gene map of the human genome

The human genome is thought to harbor 50,000 to 100,000 genes, of which about half have been sampled to date in the form of expressed sequence tags. An international consortium was organized to develop and map gene-based sequence tagged site markers on a set of two radiation hybrid panels and a yeast artificial chromosome library. More than 16,000 human genes have been mapped relative to a framework map that contains about 1000 polymorphic genetic markers. The gene map unifies the existing genetic and physical maps with the nucleotide and protein sequence databases in a fashion that should speed the discovery of genes underlying inherited human disease. The integrated resource is available through a site on the World Wide Web at http://www.ncbi.nlm.nih.gov/SCIENCE96/.

Mood disorder and chronic hypercalcemia

Fifty-five patients with chronic hypercalcemia were compared with test norms, and two comparison groups of orthopedic patients and hypertensive patients on objective and subjective tests of mood. Sixteen percent of the hypercalcemic patients were found to score over the cut-off point for anxiety on the anxiety subsection of the Hospital Anxiety and Depression Scale, and 16% were diagnosed as suffering from depression on the Paykel Clinical Interview for Depression. There were, however, no significant differences between the comparison groups and those with hypercalcemia on the scales used. There has been debate about the management of individuals with hypercalcemia. This study supports a conservative rather than a surgical approach as far as psychological symptoms are concerned.

Prodrugs of BMS-183920: metabolism and permeability considerations

The oral bioavailability of BMS-183920, a diacidic, potent angiotensin II receptor antagonist, is low in rats (approximately 11%). In vivo studies in bile duct-cannulated rats indicated that BMS-183920 was metabolically stable and that the low bioavailability was due to incomplete intestinal absorption. Five acyl-ester prodrugs were synthesized which were 5-15 times more permeable than BMS-183920 through Caco-2 cells. However, limited studies in rats indicated that the oral bioavailability of BMS-183920 was improved only 2-fold, in the best case. The lack of a substantial increase in bioavailability was apparently due to presystemic prodrug hydrolysis or metabolism via N-glucuronidation. Bioavailability of BMS-183920 after oral dosing of a tetrazole-ester prodrug averaged 37%, the most significant improvement within this prodrug series. Interestingly, in vitro studies indicated that the tetrazole-ester prodrug was a substrate for glucuronosyl transferase; however, its rate of bioactivation (hydrolysis) was sufficiently high to provide a substantial increase in bioavailability of BMS-183920. Therefore, while prodrug modification of BMS-183920 improved Caco-2 cell permeability and oral absorption in vivo, the relative extents of hydrolysis (bioactivation) vs metabolism of the prodrug determined whether a substantial improvement in bioavailability was achieved.

Coronary disease risk factor reduction and behavior modification in minority adolescents: the PATH program

PURPOSE

To evaluate the impact of a unique school-based program of exercise, health education, and behavior modification on health knowledge, health behaviors, coronary risk factors, and cardiovascular fitness in minority adolescents.

METHODS

A total of 346 students from an inner-city public high school participated in health promotion intervention or regular physical education volleyball classes. Subjects were African-American (47%), Asian-American (9%), Hispanic (21%), white (3%), and other (19%). The health promotion curriculum consisted of 11 weeks of daily circuit training exercise and health lecture-discussions.

RESULTS

The groups were similar in age, height, weight, ethnicity, and socioeconomic status. Following intervention both boys (P < .001) and girls (P < .006) significantly improved health knowledge test scores. Significant benefits for girls included improved dietary habits (P < .05), reduced cholesterol (P < .004), and higher estimated V(O2)max (P < .0001). There were no other significant changes in boys.

CONCLUSIONS

The results suggest that a school-based health promotion program of exercise and health lecture-discussion is beneficial for multiethnic, inner-city adolescents, especially females.

X-ray diffraction analysis of cytochrome P450 2B4 reconstituted into liposomes

Two general models of the membrane topology of microsomal cytochrome P450 have been proposed: (1) deep immersion in the membrane, and (2) a P450cam-like heme domain anchored to the membrane with one or two membrane-spanning helices. Lamellar X-ray diffraction of oriented membrane multilayers was employed to distinguish these alternatives. Cytochrome P450 2B4 was reconstituted into unilamellar phospholipid proteoliposomes (molar protein to lipid ratio 1:90). Sedimentation of the proteoliposomes produced an ordered stack of bilayers with a one-dimensional repeat distance (d) perpendicular to the plane of the bilayer. The stacked multilayers were exposed to an X-ray beam (lambda = 1.54 A) at near grazing incidence, and lamellar diffraction patterns were recorded. With proteoliposome multilayers, up to six diffraction orders could be observed. Their spacing corresponded to a d of 63.6 A, calculated according to Bragg's Law, comprising the lipid bilayer, the projection of the incorporated protein beyond the bilayer, and the intermembrane water layer. With liposome multilayers containing no P450, the observed d was 59.6 A. These data suggest that the increase of distance between successive bilayers in the stack due to the presence of P450 2B4 was only about 4 A. This distance is much less than would be expected with the "N-terminal membrane-anchor" model of the membrane topology, in which the P450 molecules largely extend beyond the surface of the membrane (> or = 35 A). Furthermore, the mass distribution deduced from Fourier synthesis confirms that the protein is deeply immersed in the membrane.

Somatostatin stimulates BKCa channels in rat pituitary tumor cells through lipoxygenase metabolites of arachidonic acid

The stimulation of large-conductance, calcium-activated (BK) potassium channels by somatostatin through protein dephosphorylation in rat pituitary tumor cells (White et al., Nature 351, 570-573, 1991) is blocked by drugs that interfere with arachidonic acid release by phospholipase A2 and metabolism by 5-lip-oxygenase. In contrast, higher concentrations of the same drugs had no effect on BK channel gating in cell-free patches, on the inhibition of adenylyl cyclase by somatostatin, or on the stimulation of BK channels by protein dephosphorylation through a cGMP-dependent pathway (White et al., Nature 361, 263-266, 1993). Exogenous arachidonic acid (1-20 muM) stimulated BK channel activity through protein dephosphorylation as effectively as somatostatin and was also blocked by inhibitors of lipoxygenases but not by inhibitors of phospholipase A2. These results support the hypothesis that lipoxygenase metabolites of arachidonic acid are second messengers linking pertussis toxin sensitive G-proteins to protein phosphatases regulating potassium channel activity (Armstrong and White, Trends Neurosci. 15, 403-408, 1992).

Estrogen relaxes coronary arteries by opening BKCa channels through a cGMP-dependent mechanism

Women rarely suffer cardiovascular dysfunction before menopause, but by the age of 65 a woman becomes as vulnerable to cardiovascular mortality as a man. It has been proposed that estrogens protect against cardiovascular disease; however, the physiological basis of estrogen protection is unknown. In the present study the mechanism of estrogen-induced relaxation of coronary arteries was investigated at the tissue, cellular, and molecular levels. Tissue studies demonstrate that 17 beta-estradiol relaxes porcine coronary arteries by an endothelium-independent mechanism involving K+ efflux, and subsequent studies employing the patch-clamp technique confirmed that estrogen stimulates K+ channel gating in coronary smooth muscle. Perforated-patch recordings from metabolically intact coronary myocytes revealed that 17 beta-estradiol more than doubles steady state outward currents in these cells at positive voltages. Studies of on-cell patches demonstrated a potent stimulatory effect of 17 beta-estradiol on the gating of the large-conductance, Ca(2+)- and voltage-activated K+ (BKCa) channels, while 17 alpha-estradiol had no effect. Furthermore, blocking BKCa channels in intact arteries inhibited estrogen-induced relaxation. The effect of 17 beta-estradiol on BKCa channels was blocked by inhibiting cGMP-dependent protein kinase (PKG) activity and was mimicked by exogenous cGMP or by stimulating PKG activity. Therefore, we propose that 17 beta-estradiol relaxes coronary arteries by opening BKCa channels via cGMP-dependent phosphorylation. This novel mechanism could account for the hypotensive effect of estrogens and help explain, at least in part, why postmenopausal estrogen therapy lowers the risk of cardiovascular disease.

A three-dimensional model of aromatase cytochrome P450

P450 hemeproteins comprise a large gene superfamily that catalyzes monooxygenase reactions in the presence of a redox partner. Because the mammalian members are, without exception, membrane-bound proteins, they have resisted structure-function analysis by means of X-ray crystallographic methods. Among P450-catalyzed reactions, the aromatase reaction that catalyzes the conversion of C19 steroids to estrogens is one of the most complex and least understood. Thus, to better understand the reaction mechanism, we have constructed a three-dimensional model of P450arom not only to examine the active site and those residues potentially involved in catalysis, but to study other important structural features such as substrate recognition and redox-partner binding, which require examination of the entire molecule (excepting the putative membrane-spanning region). This model of P450arom was built based on a "core structure" identified from the structures of the soluble, bacterial P450s (P450cam, P450terp, and P450BM-P) rather than by molecular replacement, after which the less conserved elements and loops were added in a rational fashion. Minimization and dynamic simulations were used to optimize the model and the reasonableness of the structure was evaluated. From this model we have postulated a membrane-associated hydrophobic region of aliphatic and aromatic residues involved in substrate recognition, a redox-partner binding region that may be unique compared to other P450s, as well as residues involved in active site orientation of substrates and an inhibitor of P450arom, namely vorozole. We also have proposed a scheme for the reaction mechanism in which a "threonine switch" determines whether oxygen insertion into the substrate molecule involves an oxygen radical or a peroxide intermediate.

Effects of bioflavonoids on hepatic P450 activities

1. The effects of tangeretin, green tea flavonoids, and other flavonoids on 7-ethoxyresorufin-O-deethylase (EROD; 450 1A), 7-pentoxyresorufin-O-dealkylase (PROD; P450 2B), p-nitrophenol hydroxylase (PNPH, P450 2E1), and erythromycin-N-demethylase (ERDM; P450 3A) were examined in induced rat liver microsomes. EROD, PNPH, ERDM, and nifedipine oxidase (NIFO; P450 3A4) were examined in human liver microsomes. 2. All flavonoids tested inhibited EROD activity at higher concentrations in liver microsomes. Flavone and tangeretin were potent inhibitors of EROD, with IC50's of 0.7 and 0.8 microM respectively in rat liver microsomes and 0.15 and 16 microM respectively in human liver microsomes. The green tea flavonoid (-)-epicatechin-3-gallate (ECG) was the most potent inhibitor of EROD in human liver microsomes (IC50 = 75 microM). The effect of the green tea flavonoids on EROD was complex; in addition to inhibition at high concentrations of flavonoid, moderate activation was seen at lower concentrations. 3. 450 2B-, 2E1- and 3A-dependent activities in rat and human liver microsomes were only moderately inhibited by any of the flavonoids tested, and, in general, ECG was the most potent inhibitor for these activities with IC50's ranging from 75 to 300 microM. 4. Tangeretin inhibited EROD activity (P450 1A2) in human liver microsomes in a competitive manner with a Ki = 68 nM. Tangeretin inhibited NIFO activity (P450 3A4) in human liver microsomes in an uncompetitive manner with Ki = 72 microM.

Prevalence estimates of alcohol problems in a Veterans Administration outpatient population: AUDIT vs. MAST

Prior reports have indicated that the prevalence of alcohol-related problems in VA patients is significantly higher than that found in the general population. Prevalence rates, however, are likely to be affected by the screening instrument employed. A sample of 722 VA outpatients awaiting general medical and urgent care treatment was asked to complete two screening questionnaires: the World Health Organization's AUDIT and the brief MAST. Of 508 completed AUDITs, 55 (11%) scored above the cut-offs of 11 for harmful consumption, and 85 (17%) above the more liberal cut-off score of 8; whereas of 501 completed MASTs, 104 (21%) scored above the cut-off. Differences in identification rates are discussed.

Uncertainty and psychologic stress after coronary angioplasty and coronary bypass surgery

OBJECTIVE

To examine the trajectory of uncertainty and symptoms of psychologic stress during the first 3 months after coronary angioplasty and coronary bypass surgery and to study the impact of social support on uncertainty and psychologic stress in these patient populations.

DESIGN

Descriptive, correlative.

SETTING

Urban community, at-home interviews.

PATIENTS

Male patients with angioplasty (n = 22) and bypass (n = 25) at 1 and 3 months after treatment. Age range was 39 to 75 years (mean 58 years).

OUTCOME MEASURES

Mishel Uncertainty in Illness scores, General Health Questionnaire scores, and Perceived Social Support Scale scores.

INTERVENTION

Patients underwent either percutaneous transluminal coronary angioplasty or coronary artery bypass grafting as treatment for coronary artery disease.

RESULTS

Data were analyzed with repeated measures analysis of variance and Pearson correlation coefficients. Results showed that at both time periods angioplasty patients were more uncertain than bypass patients (p < 0.05), and that regardless of procedure, patients reported fewer symptoms of psychologic stress at 3 months than at 1 month (p < 0.01). Patients with high social support had less uncertainty and psychologic stress than patients with low support (p < 0.05). Analysis of the social support and treatment group interaction showed that angioplasty patients with low perceived social support had significantly more psychologic stress than angioplasty patients with high support (p < 0.01). Analysis of the correlations between uncertainty and psychologic stress in the angioplasty and bypass grafting procedure groups after control for social support revealed that social support was a significant mediator of the relationship between uncertainty and stress only among patients undergoing percutaneous transluminal coronary angioplasty. There was little evidence of a mediating role for social support in the coronary artery bypass grafting group.

CONCLUSIONS

These results suggest that angioplasty patients may be in particular need of interventions aimed at reducing uncertainty, and that interventions that increase social support could be important in achieving this reduction.

Health promotion in minority adolescents: a Healthy People 2000 pilot study

PURPOSE

The purpose was to evaluate the effects of a health promotion curriculum on health knowledge, behavior, cardiovascular fitness, and cardiovascular risk factors.

METHODS

A multi-ethnic, multi-cultural sample (n = 54) of 10th grade males and females participated in a study of cardiovascular health promotion and coronary risk factor reduction. The sample was comprised of Asian-Americans (39%), blacks (33%), Hispanics (11%), whites (2%), and others (15%). Intervention consisted of a 10-week health promotion curriculum of classroom education modules in physical activity, nutrition, smoking cessation, stress management and personal problem solving, and an exercise program of walking and running. A nonintervention control group served as a basis for comparison. Classroom and exercise sessions met on alternate days.

RESULTS

Following intervention, a significant treatment effect (P = .007) was observed in lowered total cholesterol, and significant within group improvements (P < .01) were observed in diet habits, percent body fat, and cardiovascular health knowledge. Comparisons of knowledge and social effects revealed higher cardiovascular health knowledge (P < .05) in subjects of nonsmoking compared to smoking parents, higher self-perception of health (P < .01) in more active vs less active subjects and better dietary habits (P < .07) in children whose parents were college educated compared to parents who did not attend college.

CONCLUSIONS

Preliminary findings suggest that a health promotion curriculum consisting of health education, behavior modification, and regular aerobic exercise lowers cholesterol, improves health behavior and increases health knowledge.

Photoaffinity labeling of cytochrome P450 2B4: capture of active site heme ligands by a photocarbene

Spiro[adamantane-2,2'-diazirine], which produces adamantyl carbene upon photolysis, binds tightly to P450 2B4 (KS = 3.2 microM), giving a normal substrate binding difference spectrum. Irradiation of 2-[3H]adamantane diazirine at 365 nm in the presence of native, ferric P450 2B4 resulted in first-order photolysis (t1/2 = 1.8 min). The main product was 2-[3H]adamantanol, with about 6% of the radioactivity covalently bound to P450 2B4. With the ferrous carbonyl form of P450 2B4, 2-adamantanol production decreased and protein labeling increased to 12%. When ferric cyanide 2B4 was used, 2-adamantanecarbonitrile was formed in addition to 2-adamantanol. The nitrile appears to have resulted from capture of the iron-bound cyanide ligand by the carbene. The use of multiple cycles of photolysis increased the percentage of protein labeling to 76%. Photolabeling was inhibited by known 2B4 substrates and inhibitors. Also, N-demethylation of benzphetamine and generation of a substrate binding difference spectrum by benzphetamine were both inhibited stoichiometrically with the fraction of radiolabeled protein. The labeled protein was permanently converted to the high-spin state, as indicated by the characteristic change in the absorbance spectrum, demonstrating irreversible occupation of the substrate binding site by the adamantyl residue. Mild acid hydrolysis of radiolabeled 2B4 at the five Asp-Pro bonds generated a 2-kDa peptide which carried 78% of the radioactivity. These results are interpreted as the result of the active site carbene reacting by three competing pathways: capture of the heme sixth ligand to yield either 2-adamantanol or 2-adamantanecarbonitrile, capture of an unbound active site water molecule to yield adamantanol, and covalent attachment to a protein residue. Thus, the P450 2B4 active site appears to contain at least one unbound water molecule in addition to the heme aquo sixth ligand, even when substrate is present.

Data-driven performance improvement in health care: the Joint Commission's Indicator Measurement System (IMSystem)

BACKGROUND

Since 1986, the Joint Commission has worked to create an evaluation system that would remain standards based but would accent an organization's performance as well as its capability to provide care. One component is the Indicator Measurement System (IMSystem), which involves continuous data collection and periodic feedback about specific performance measures, or indicators. An indicator is a quantitative measure of an aspect of patient care. It is not a direct measure of quality; rather it is a screen or flag which indicates areas for more detailed analysis.

METHODOLOGY

Sets of indicators, each set related to specific important health care functions such as perioperative care, are established by expert task forces and are then subject to two phases of testing. Alpha testing addresses face validity and feasibility of data collection and may result in indicator revision. In the beta phase, a large group of organizations test the indicators for validity, reliability, and usefulness in improving performance.

OPERATIONAL ISSUES

In 1994, the IMSystem will contain ten indicators and participation by hospitals will be voluntary. Once the value of these data in the accreditation process has been demonstrated--possibly as early as 1996--participation will become an integral component of accreditation. Hospitals will transmit indicator data to the Joint Commission but no patient or physician identifiers will leave the hospital. The system will provide organizations with information they can use to monitor and improve their performance, while helping meet external needs for performance measurement.

Kallmann's syndrome and anorexia nervosa: a diagnostic dilemma

Kallmann's syndrome is a rare cause of primary amenorrhea, with impairment of release of gonadotropin-releasing hormone and anosmia. We present a case in which Kallmann's syndrome had been diagnosed, but who also fulfilled the diagnostic criteria for anorexia nervosa. We discuss the diagnostic dilemma.

Potassium channel stimulation by natriuretic peptides through cGMP-dependent dephosphorylation

Natriuretic peptides inhibit the release and action of many hormones through cyclic guanosine monophosphate (cGMP), but the mechanism of cGMP action is unclear. In frog ventricular muscle and guinea-pig hippocampal neurons, cGMP inhibits voltage-activated Ca2+ currents by stimulating phosphodiesterase activity and reducing intracellular cyclic AMP; however, this mechanism is not involved in the action of cGMP on other channels or on Ca2+ channels in other cells. Natriuretic peptide receptors in the rat pituitary also stimulate guanylyl cyclase activity but inhibit secretion by increasing membrane conductance to potassium. In an electrophysiological study on rat pituitary tumour cells, we identified the large-conductance, calcium- and voltage-activated potassium channels (BK) as the primary target of another inhibitory neuropeptide, somatostatin. Here we report that atrial natriuretic peptide also stimulates BK channel activity in GH4C1 cells through protein dephosphorylation. Unlike somatostatin, however, the effect of atrial natriuretic peptide on BK channel activity is preceded by a rapid and potent stimulation of cGMP production and requires cGMP-dependent protein kinase activity. Protein phosphatase activation by cGMP-dependent kinase could explain the inhibitory effects of natriuretic peptides on electrical excitability and the antagonism of cGMP and cAMP in many systems.

An enzymatic mechanism for potassium channel stimulation through pertussis-toxin-sensitive G proteins

Many neurotransmitters inhibit secretion from electrically excitable cells by activating pertussis-toxin-sensitive G proteins that modulate voltage-gated ion channels. Recent electrophysiological studies of metabolically intact cells from mammalian and molluscan neuroendocrine systems have implicated protein phosphatases in this process. In this article David Armstrong and Richard White review these studies and suggest a biochemical pathway that might link one of the G proteins to protein phosphatase activity.