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B Cromer

Publications and source records attributed to B Cromer.

14 recordsLinked to original sources
PubMed2005

A role for the 2' residue in the second transmembrane helix of the GABA A receptor gamma2S subunit in channel conductance and gating.

GABA(A) receptors composed of alpha, beta and gamma subunits display a significantly higher single-channel conductance than receptors comprised of only alpha and beta subunits. The pore of GABA(A) receptors is lined by the second transmembrane region from each of its five subunits and includes conserved threonines at the 6', 10' and 13' positions. At the 2' position, however, a polar residue is present in the gamma subunit but not the alpha or beta subunits. As residues at the 2', 6' and 10' positions are exposed in the open channel and as such polar channel-lining residues may interact with permeant ions by substituting for water interactions, we compared both the single-channel conductance and the kinetic properties of wild-type alpha1beta1 and alpha1beta1gamma2S receptors with two mutant receptors, alphabetagamma(S2'A) and alphabetagamma(S2'V). We found that the single-channel conductance of both mutant alphabetagamma receptors was significantly decreased with respect to wild-type alphabetagamma, with the presence of the larger valine side chain having the greatest effect. However, the conductance of the mutant alphabetagamma receptors remained larger than wild-type alphabeta channels. This reduction in the conductance of mutant alphabetagamma receptors was observed at depolarized potentials only (E(Cl) = -1.8 mV), which revealed an asymmetry in the ion conduction pathway mediated by the gamma2' residue. The substitutions at the gamma2' serine residue also altered the gating properties of the channel in addition to the effects on the conductance with the open probability of the mutant channels being decreased while the mean open time increased. The data presented in this study show that residues at the 2' position in M2 of the gamma subunit affects both single-channel conductance and receptor kinetics.

Amino Acid Substitution↗
PubMed2001

Selections from current literature: Recent developments in human HIV-1 vaccine.

This article reviews recent changes in the design of HIV-I vaccine. The safety information for current vaccines has been established, and future ethical considerations are reviewed. Of recent significance, gp120 envelope vaccines are being combined with canarypox vectors in an effort to elicit a broad immune response. This will probably be the aim of future research for an ever-growing problem. A total of 10 143 AIDS cases have occurred in the USA in the year 2000.(1) The international burden is grimmer. For example, approximately 13% of South Africans between 20 and 64 years old are HIV positive. Predictions estimate this number to rise to almost 30% by 2010.(2) With many different HIV serotypes, a worldwide effective HIV vaccine is not in the near future.(3) However, the scientific community has bolstered its effort by strengthening resources and developing national and international collaboration groups focused in developing a safe and effective HIV vaccine.

AIDS Vaccines↗
PubMed2000

Update on adolescent contraception.

Recent advances in OCPs include less androgenic progestins and lower doses of ethinyl estradiol. All low-dose OCPs are safe in terms of venous thrombosis risk in appropriately chosen patients. DMPA is a safe and effective long-acting contraceptive agent; clinical attention should be directed to its most common side effect, irregular bleeding. DMPA does not seem to affect mood, and it is uncertain what impact it has on weight changes. More research needs to be conducted on its impact on adolescent bone metabolism. Norplant continues to be the only subdermal contraceptive implant marketed in the United States. It provides safe and effective contraception and has the best continuation rate of all types of hormonal contraception. Its most common side effect is irregular bleeding. Norplant may be especially well suited for adolescents who have recently been pregnant or who are not tolerating other types of contraception. Emergency postcoital contraception continues to be underused in the United States, with a lack of awareness among patients and clinicians. Mechanisms of action include a delay in ovulation and interference with implantation. Research and public health groups are striving to increase patient and provider awareness and use of emergency contraception.

Adolescent↗
PubMed2000

Adolescents: at increased risk for osteoporosis?

Perhaps the most important factor in the primary prevention of osteoporosis is the attainment of an optimal peak bone during adolescence. In addition to endogenous factors, such as genetic and ethnic background, environmental factors such as dietary habits, physical activity, and sex hormone therapy, influence the accretion of bone mass during this critical period of skeletal growth. First, calcium dietary intake in adolescents is generally well less than the current recommended RDA of 1200 mg/day. Multiple studies of children and adolescents have demonstrated increases in bone mass with dietary calcium supplementation. Second, regarding physical activity, the overall impression is that a moderate amount of particularly weight-bearing exercise has a positive impact on bone. There appears, however, to be a threshold of intensity of physical activity over which a negative impact on bone occurs, particularly when the exercise is of an anaerobic nature or occurring in very thin, amenorrheic participants. Third, previous research suggests that the various forms of hormonal contraception exert differing effects on bone mass in adolescents, with levonorgestrel implants and combined oral contraceptives may be associated with a more positive effect on bone mass compared with that observed with depot medroxyprogesterone acetate. From a clinical perspective, approaches to optimizing peak bone mass in adolescents would include increasing calcium intake, whether in the form of dairy products, fortified foods, or supplements as well as encouraging participation at a moderate level, in weight-bearing exercise. Last, in adolescents with extensive risk factors and predicted long duration of use, subdermal implants or combined oral contraceptives may be the optimal hormonal methods of birth control.

Adolescent↗
PubMed1999

The use of long-acting contraceptives in adolescents.

DMPA and implants have played an important role in the attempt to prevent teenage pregnancies. Adolescent health care providers should provide continued counseling to girls using DMPA or implants and should promptly address any concern associated with these methods. Future studies are warranted to explore ways to prevent or reduce the side effects of DMPA and implants, as well as to develop new, optimal, long-acting contraceptives. Detailed baseline information should be obtained in every future study that explores the presence of side effects during the use of long-acting contraceptives.

Adolescent↗
PubMed1998

Two threonine residues in the M2 segment of the alpha 1 beta 1 GABAA receptor are critical for ion channel function.

The role of three threonine residues in the M2 hydrophobic region of the GABAA receptor has been investigated by replacing these polar residues with alanine at the 6', 10' and 13' positions of M2 in the GABAA alpha 1, and beta 1 subunits and co-expressing the mutated subunits in the baculovirus Sf9 insect cell system. GABA did not elicit a current in cells expressing either the 6' or 13' threonine to the alanine mutants. The mutant subunits formed intact heteromeric GABAA receptors as judged by the binding of [3H] muscimol or the relative level of alpha 1 protein present in the plasma membrane. In contrast, a chloride current was generated by GABA in cells expressing the 10' mutant receptor. However, the current decayed more rapidly to baseline in the continued presence of GABA in the 10' mutant receptor than in the wild type receptor. The results are discussed in terms of the possible roles of the threonine residues in the ion conduction pathway.

Alanine↗
PubMed1992

Different 1,4-dihydropyridines exhibit discriminating effects on passive calcium uptake in rat liver plasma membrane vesicles.

The effects of a number of calcium channel effectors on Ca2+ uptake by rat liver plasma membrane vesicles was examined. Nifedipine, verapamil and diltiazem had to be present at 1 mM in order to produce > 50% inhibition of Ca2+ uptake. The two structurally similar 1,4-dihydropyridines, nicardipine and nisoldipine exhibited opposite effects; nicardipine inhibited while nisoldipine stimulated Ca2+ uptake. The results show that low concentrations (microM) of calcium channel blockers of excitable cells have little effect on Ca2+ uptake by liver plasma membrane vesicles consistent with earlier findings of others that voltage-gated calcium channels are absent in hepatocytes. However, the opposite effects of higher concentrations (ca. 1 mM) of nicardipine and nisoldipine on Ca2+ uptake suggest a discriminatory action that might be useful in studying further the mechanism of passive Ca2+ uptake by these membrane vesicles.

Animals↗
PubMed1992

Acute effect of consumption/omission of breakfast on exercise tolerance in adolescents.

The purpose of this study was to determine the acute effects of the consumption or omission of breakfast on exercise tolerance in adolescents. Physically active adolescents (14 males and 21 females) were randomly assigned to receive a breakfast (B) or placebo (P) after an overnight fast. Exercise tolerance tests were done 1.5 hours (test 1) and again 4 hours (test 2) after consuming B or P and consisted of cycling on a stationary bike for 4 minutes at each of four consecutive power settings: 25, 50, 75, and 100 watts. Blood glucose and beta-hydroxybutyrate concentrations were measured before both tests. VO2 and VCO2 were measured during minute 3 of cycling at loads 50 and 75 watts and were used to compute the respiratory exchange ratio (RER). Heart rates (HR) were monitored throughout the test and ratings of perceived exertion (RPE) were made at the end of each 4 min interval. Repeated measures ANOVA revealed that there were no differences in RPE; however, differences for HR and RER did exist. Mean RER values were higher for the males receiving B vs males receiving P during test 1. For females, HR were higher for P compared B, and beta-hydroxybutyrate was significantly elevated for P before test 2. The data suggest that exercise tolerance as indicated by the ratings of perceived exertion are unaffected by prior ingestion of a breakfast but breakfast does affect the physiologic responses to exercise.

Adolescent↗
PubMed1989

Riboflavin status in urban adolescents.

We compared riboflavin status in 284 healthy adolescents attending an urban university hospital clinic with that of 43 adolescents with a variety of chronic medical conditions. Riboflavin status was determined by erythrocyte glutathione reductase activity and 24-hour dietary recall of riboflavin intake. The mean activity coefficient for the healthy adolescents was 1.08 (SD +/- 0.09) and 1.10 (SD +/- 1.01) in the chronically ill group. Significantly higher values were found in females of both groups (z = 4.90, p less than 0.0001). Seventeen (7%) of the healthy teenagers and seven (16%) of the chronically ill group had biochemical evidence of riboflavin deficiency (p less than 0.02). Although the mean daily intake of riboflavin for the total group exceeded the recommended daily allowance, there was significantly lower riboflavin intake in the subgroup of adolescents who had abnormal activity coefficients (z = 3.29, p less than 0.001). These data suggest that subclinical riboflavin deficiency may occur in adolescents and that deficiency may be related to dietary intake of riboflavin.

Adolescent↗
PubMed1988

An inventory to measure medical staff knowledge of behavioral methods with pediatric pain patients.

An inventory is described for assessing medical staffs' knowledge of behavioral methods with pediatric pain patients. It was adapted from a measure designed by Sanders and Webster (1982) for use with nurses treating adult chronic pain patients. The modified inventory was administered to three groups of medical staff: (a) pediatric residents, (b) pediatric nurses and (c) medical students. A series of analyses provided data supporting the psychometric integrity of the inventory. The measure successfully discriminated trained from untrained staff. The utility of the instrument for staff assessment and development is discussed.

Adult↗
PubMed1987

Increasing appointment compliance through telephone reminders: does it ring true?

This study evaluated the effectiveness of telephone reminders on appointment-keeping in young people treated for gonorrhea. Compliance with scheduled follow-up was recorded for a total of 339 patients during three two-week periods, namely, initial baseline phase, intervention phase during which attempts were made to remind the patients by telephone, and repeat baseline phase. There was no overall improvement in compliance with follow-up during intervention (31%), compared to baseline (32%). However, data from the intervention phase revealed a significantly higher rate of appointment-keeping for those patients who were contacted (44%) than for patients who were not reachable (20%). Furthermore, when we reanalyzed the data as a function of telephone ownership for all patients who did not receive a reminder, return rates were significantly higher for patients owning telephones (32%) than for those denying phone ownership (18%). Thus, we conclude that the likelihood for appointment compliance was related more to sociobehavioral factors reflected in telephone ownership than to the telephone reminders.

Adolescent↗
PubMedDate not supplied

Abortion in adolescence: a four-country comparison.

The purpose of this study was to conduct a comparison, using qualitative analytic methodology, of perceptions concerning abortion among health care providers and administrators, along with politicians and anti-abortion activists (total n = 75) in Great Britain, Sweden, The Netherlands, and the United States. In none of these countries was there consensus about abortion prior to legalization, and, in all countries, public discussion continues to be present. In general, after legalization of abortion has no longer made it a volatile issue European countries have refocused their energy into providing family planning services, education, and more straightforward access to abortion compared with similar activities in the United States.

Abortion, Induced↗