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Biomedical subjects

R E White

Publications and source records attributed to R E White.

At least 37 records · Page 2Linked to original sources
PubMed2000

H(2)O(2) opens BK(Ca) channels via the PLA(2)-arachidonic acid signaling cascade in coronary artery smooth muscle.

H(2)O(2) is a reactive oxygen species that contracts or relaxes vascular smooth muscle, but the molecular basis of these effects remains obscure. We previously demonstrated that H(2)O(2) opens the large-conductance, calcium- and voltage-activated (BK(Ca)) potassium channel of coronary myocytes (2) and now report physiological and biochemical evidence that the effect of H(2)O(2) on coronary smooth muscle involves the phospholipase A(2) (PLA(2))/arachidonic acid (AA) signaling cascades. H(2)O(2) stimulation of BK(Ca) channel activity was inhibited by arachidonyl trifluoromethyl ketone, an inhibitor of cytosolic PLA(2). Furthermore, H(2)O(2) stimulated release of [(3)H]AA from coronary myocytes, and exogenous AA mimicked the effect of H(2)O(2) on BK(Ca) channels. Inhibitors of protein kinase C activity attenuated the effect of H(2)O(2) on BK(Ca) channels, [(3)H]AA release, or intact coronary arteries. In addition, the effect of H(2)O(2) or AA on BK(Ca) channels was inhibited by blockers of lipoxygenase metabolism. In contrast, inhibitors of cyclooxygenase or cytochrome P-450 had no effect. We propose that H(2)O(2) relaxes coronary arteries by stimulating BK(Ca) channels via the PLA(2)/AA signaling cascade and that lipoxygenase metabolites mediate this response.

Animals↗
PubMed1999

Resveratrol inhibits MAPK activity and nuclear translocation in coronary artery smooth muscle: reversal of endothelin-1 stimulatory effects.

In porcine coronary arteries, short-term treatment with resveratrol (RSVL) substantially inhibited MAPK activity (IC50 = 37 microM); and immunoblot analyses revealed consistent reduction in the phosphorylation of ERK-1/-2, JNK-1 and p38, at active sites. Endothelin-1 (ET-1), a primary antecedent in coronary heart diseases, enhanced MAPK activity, phosphorylation and nuclear translocation in a concentration-responsive but RSVL-sensitive manner. RSVL had no effect on basal or forskolin-stimulated cAMP levels, a known downregulator of the MAPK cascade. Likewise, inhibition of MAPK by RSVL was not reversed by the estrogen receptor blockers tamoxifen and ICI-182,780. Conversely, RSVL remarkably attenuated basal and ET-1-evoked protein tyrosine phosphorylation. Because MAPKs promote smooth muscle proliferation and contraction, their current inhibition may contribute to the putative protection by RSVL against coronary heart diseases. These effects apparently do not involve interaction with estrogen receptors.

Animals↗
PubMed1999

A novel transduction mechanism mediating dopamine-induced vascular relaxation: opening of BKCa channels by cyclic AMP-induced stimulation of the cyclic GMP-dependent protein kinase.

Dopamine dilates the coronary, renal and other vascular beds; however, the signaling pathway underlying this effect is unclear. In this study the signal-transduction process mediating dopamine-induced relaxation of porcine coronary arteries was investigated in isolated vessels and single arterial myocytes. Dopamine-induced relaxation of arteries was mediated through the DA- receptor and involved K+ efflux, and subsequent patch-clamp studies demonstrated that either dopamine or fenoldopam, a selective DA-1 agonist, increased the opening probability of the large-conductance, calcium- and voltage-activated K+ (BKCa) channel in coronary myocytes. Moreover, blockade of this channel by iberiotoxin prevented dopamine-induced coronary relaxation. Dopamine stimulation of BKCa channels was completely prevented by a DA-1-receptor antagonist, but was unaffected by propranolol. Furthermore, inhibiting adenylyl cyclase activity prevented stimulation of BKCa channel activity, whereas chlorophenylthio (CPT)-cyclic adenosine monophosphate (AMP), a membrane-permeable analog of cyclic AMP, mimicked the effects of dopamine. Interestingly, inhibiting the cyclic AMP-dependent protein kinase (PKA) did not affect the response to dopamine, whereas dopamine-induced channel activity was completely blocked by inhibiting the activity of the cyclic guanosine monophosphate (GMP)-dependent protein kinase (PKG). These findings demonstrate that activation of DA-1 receptors causes stimulation of BKCa channel activity by a mechanism involving cyclic AMP-dependent stimulation of PKG, but not PKA, and further suggest that this cross-reactivity mediates dopamine-induced coronary vasodilation.

Animals↗
PubMed1999

Clinical comparison of the midvastus and medial parapatellar surgical approaches.

The medial parapatellar approach and the midvastus approach are the two most commonly used surgical approaches in total knee replacement. This study compared surgical and clinical parameters associated with both surgical approaches in primary total knee replacement. One hundred nine patients who underwent bilateral primary total knee replacements had a medial parapatellar approach to one knee and a midvastus approach to the opposite knee. The prosthetic design and physical therapy were identical in all 109 patients. The patients and physical therapists were blinded to the type of approach used on each knee. The comparison included the surgical parameters of difficulty of exposure, surgical time, incidence of lateral retinacular release, and total blood loss. The clinical parameters of pain, range of motion, ability to perform a straight leg raise, and complications were compared at 8 days, 6 weeks and 6 months. The comparison between the two surgical approaches showed a statistically significant difference in four parameters, all of which favored the midvastus approach. The patients who had the midvastus approach required fewer lateral retinacular releases, had less pain at 8 days, had less pain at 6 weeks, and had a higher incidence of ability to straight leg raise at 8 days. There was no statistical difference between the two surgical approaches in all other surgical and clinical parameters. There was no increased difficulty of exposure using the midvastus approach when compared with the medial parapatellar approach even in patients with severe varus or valgus deformities. Notably, all clinical parameters were equal at 6 months. From a clinical standpoint, the midvastus approach had an advantage over the medial parapatellar approach because the patients had significantly less pain and had the ability to straight leg raise at 8 days. Because the managed care environment dictates a shorter hospital stay, patients who have the midvastus surgical approach have less pain and earlier control of the operative leg, and may be discharged from the hospital earlier. However, the clinical results at 6 months based on the patient's pain relief, range of motion, and ability to straight legraise were identical between the two surgical approaches.

Adult↗
PubMed1998

Evidence for a tyrosine kinase-dependent activation of the adenylyl Cyclase/PKA cascade downstream from the G-protein-linked endothelin ETA receptor in vascular smooth muscle.

Endothelin (ET-1), a contractor and mitogen in the vasculature, enhanced cAMP production (t1/2, 2.2 min; EC50, 89 +/- 6.3 nM) and stimulated activity of the cAMP-dependent protein kinase (PKA) in pig coronary arteries. These responses were blunted by the protein tyrosine kinase (PTK) inhibitors genistein and herbimycin-A, but not by inhibitors of protein kinase C or cyclooxygenase. In contrast, forskolin-stimulated cAMP production was unaffected by PTK inhibition. Immunoblot analysis revealed that ET-1 induced a concentration-dependent protein tyrosine (PT) phosphorylation. Sarafotoxin-c, a selective ETB receptor agonist, had no effect on either cAMP levels or PT phosphorylation. Moreover, pervanadate (PV), a potent inhibitor of PT phosphatases, enhanced both cAMP formation and PT phosphorylation, both of which were blocked by PTK inhibitors. The effects of ET-1 and PV were not additive, suggesting a similar mode of activation, whereas responses to ET-1 and forskolin were synergistic. These findings indicate that AC and PKA are activatable via a nonreceptor PTK-dependent pathway downstream from the G-protein-linked ETA receptor. Because cAMP is a dilator and antimitogen in smooth muscle, stimulation of AC activity may be a negative feedback mechanism regulating ET-1-induced vasoconstriction and/or mitogenesis.

Adenylyl Cyclases↗
PubMed1998

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.

Animals↗
PubMed1998

Metabolism of alpha-phosphonosulfonate squalene synthase inhibitors. I. Disposition of a farnesylethyl alpha-phosphonosulfonate and ester prodrugs in rats.

The disposition of I [(E,E)-6,10,14-trimethyl-1-phosphono-5,9, 13-pentadecatriene-1-sulfonic acid] and its mono- (II), di- (III), and triester (IV) prodrugs in rats was studied with 14C-labeled compounds. After iv administration of I (15 micromol/kg), radioactivity in plasma was measurable up to 96 hr and averaged 0. 026 microg-eq/ml. I accounted for >50% of the radioactivity in plasma and had an apparent half-life of 4 hr. After oral administration of the same dose, the maximal plasma concentration of radioactivity averaged 0.108 microg-eq/ml at 6 hr. In 96 hr, 19 and 73% of the iv dose and 2 and 97% of the po dose was excreted in urine and feces, respectively. The absorption was 2.4%, based on the plasma data. In 12 hr after an iv dose of I to bile duct-cannulated rats, 41 and 14% of the dose was excreted in bile and urine, respectively. I accounted for 51% of the radioactivity in bile and a negligible amount in urine. At 12 hr after iv dosing, liver retained 31% of the dose. No accumulation of radioactivity in bone was observed. I (3%) and II (6%) were poorly absorbed. Enhanced absorption was observed for III (80%) and IV (45%). No I or metabolites of I were found in bile or urine of rats dosed with the prodrugs. The structures of two metabolites each for I, III, and IV were proposed. Together, they accounted for >80% of the radioactivity in urine and approximately 50% of the radioactivity in bile for each compound. Metabolism appeared to occur primarily at the farnesyl moiety, presumably by the same pathways as for farnesyl-1-pyrophosphate.

Animals↗
PubMed1998

Short- and long-term projections about the use of drug metabolism in drug discovery and development.

The science of drug metabolism, like any other science, has advanced from simple beginnings (by today's standards) to its present state. One can examine the path that has been taken to understand the forces driving the direction of evolution of this science. The trends discovered can then be used to make reasonable extrapolations about the changes that might be expected in the future. That exercise is the subject of this article. The main focus will be on drug metabolism as practiced in the industrial environment, representing the author's main experience as well as the principal arena of practical applications of the science. The discussion will draw mainly on broad phenomena occurring in this application of drug metabolism to drug discovery and development.

Animals↗
PubMed1997

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.

Adult↗
PubMed1997

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.

4-Aminopyridine↗
PubMed1997

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.

Animals↗
PubMed1997

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.

Animals↗
PubMed1996

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/.

Amino Acid Sequence↗
PubMed1996

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.

Animals↗
PubMed1996

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).

Adenosine Triphosphate↗
PubMed1996

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.

Adolescent↗
PubMed1996

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.

Adult↗