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C Bender

Publications and source records attributed to C Bender.

At least 19 recordsLinked to original sources
PubMed1994

Extended sleep in humans in 14 hour nights (LD 10:14): relationship between REM density and spontaneous awakening.

The sleep patterns of 8 normal subjects living in a winter-type photoperiod (10 h light and 14 h darkness; LD 10:14) for 4 weeks were characterized by the presence of periods of spontaneous wakefulness alternating with periods of spontaneous sleep. Transitions from sleep to wakefulness occurred much more frequently out of REM sleep than out of NREM sleep (P < 0.002). REM periods that terminated in wakefulness showed shorter REM durations (P < 0.0005) and higher REM densities (P < 0.0005) than REM periods that did not terminate in wakefulness. The authors discuss these results in terms of a possible relationship between REM density and arousal level. The higher REM density preceding wakefulness and the increased number of REM periods terminating in spontaneous awakenings could reflect an enhanced level of a brain arousing process, resulting from reduced sleep pressure in the extended nights.

Adult↗
PubMed1994

Improving undergraduate biology education in a large research university.

The campus-wide Undergraduate Biology Research Program (UBRP) at the University of Arizona improves undergraduate science education by expanding student opportunities for independent research in faculty laboratories. Within the supportive community of a research laboratory, underclassmen, nonscience majors, and those aspiring to scientific careers all learn to appreciate the process of science. The Program impacts more than the students, promoting departmental cooperation, interdisciplinary collaborations, and improvements in undergraduate science education throughout a Research I University.

Adult↗
PubMed1993

Conservation of photoperiod-responsive mechanisms in humans.

In animals, circadian pacemakers respond to seasonal changes in day length by making corresponding adjustments in the durations of diurnal and nocturnal periods of circadian rhythms; these adjustments mediate effects of photoperiod on breeding and other seasonally recurring phenomena. Little is known about photoperiod responses of human circadian pacemakers. To investigate this question, we recorded and compared circadian rhythm profiles of 15 individuals after chronic exposures to short (8 h) and long (14 h) nights. As occurs in animals, durations of nocturnal periods of active melatonin secretion (11.9 +/- 1.6 vs. 10.3 +/- 1.3 h, df = 14, t = 4.583, P < 0.0005, paired t test), high prolactin secretion (12.9 +/- 2.1 vs. 9.9 +/- 2.2 h, df = 11, t = 2.917, P < 0.01), and sleep (10.6 +/- 0.8 vs. 7.6 +/- 0.4 h, df = 14, t = 17.122, P < 0.0005) were longer after exposure to long nights than after short ones. Durations of nocturnal periods of low rectal temperature (11.6 +/- 2.3 vs. 9.5 +/- 1.6 h, df = 12, t = 3.912, P < 0.001) and rising cortisol secretion (10.8 +/- 1.6 vs. 9.3 +/- 1.9 h, df = 14, t = 3.130, P < 0.005) were also longer. Some of these differences persisted during 24-h periods of enforced wakefulness in constant dim light, indicating that prior exposure to the two regimes induced abiding changes in the timing of internal processes, such as circadian pacemaker oscillations, that control the durations of nocturnal and diurnal periods of the rhythms.

Adult↗
PubMed1992

Effect of anoxia on intracellular ATP, Na+i, Ca2+i, Mg2+i, and cytotoxicity in rat hepatocytes.

The effects of anoxia were studied in freshly isolated rat hepatocytes maintained in agarose gel threads and perfused with Krebs-Henseleit bicarbonate buffer (KHB). Cytosolic free calcium (Ca2+i) was measured with aequorin, intracellular sodium (Na+i) with SBFI, intracellular pH (pHi) with BCECF, lactic dehydrogenase (LDH) by the increase in NADH absorbance during lactate oxidation to pyruvate, ATP by 31P NMR spectroscopy in real time, and intracellular free Mg2+ (Mg2+i) from the chemical shift of beta-ATP relative to alpha-ATP in the NMR spectra. Anoxia was induced by perfusing the cells with KHB saturated with 95% N2, 5% CO2. After 1 h of anoxia, beta-ATP fell 66%, and 85% after 2 h, while the Pi/ATP ratio increased 10-fold from 2.75 to 28.3. Under control conditions, the resting cytosolic free calcium was 127 +/- 6 nM. Anoxia increased Ca2+i in two distinct phases: a first rise occurred within 15 min and reached a mean value of 389 +/- 35 nM (p less than 0.001). A second peak reached a maximum value of 1.45 +/- 0.12 microM (p less than 0.001) after 1 h. During the first hour of anoxia, Na+i increased from 15.9 +/- 2.4 mM to 32.2 +/- 1.2 mM (p less than 0.001), Mg2+i doubled from 0.51 +/- 0.05 to 1.12 +/- 0.01 mM (p less than 0.001), and pHi decreased from 7.41 +/- 0.03 to 7.06 +/- 0.1 (p less than 0.001). LDH release doubled during the first hour and increased 6-fold during the second hour of anoxia. Upon reoxygenation, ATP, Ca2+i, Mg2+i, Na+i, and LDH returned near the control levels within 45 min. To determine whether the increased LDH release was related to the rise in Ca2+i, and whether the increased Ca2+i was caused by Ca2+ influx, the cells were perfused with Ca(2+)-free KHB (+ 0.1 mM EGTA) during the anoxic period. After 2 h of anoxia in Ca(2+)-free medium, beta-ATP again fell 90%, but Ca2+i, after the first initial peak, fell below control levels, and LDH release increased only 2.7-fold. During reoxygenation, Ca2+i, ATP, Na+i, and LDH returned near the control levels within 45 min. These results suggest that the rise in Ca2+i induced by anoxia is caused by an influx of Ca2+ from the extracellular fluid, and that LDH release and cell injury may be related to the resulting rise in Ca2+i.

Adenosine Triphosphate↗
PubMed1991

Effects of pH on Ca2+i, Na+i, and pHi of MDCK cells: Na(+)-Ca2+ and Na(+)-H+ antiporter interactions.

The effects of high and low extracellular pH (8.0 and 6.8) on the intracellular concentration of Ca2+, Na+, and H+ were measured in perfused Madin-Darby canine kidney (MDCK) cells cast in agarose gel threads. Cytosolic free Ca2+ (Ca2+i) was measured with aequorin, while intracellular Na+ (Na+i) and H+ (Hi+ or pHi) were determined with the fluorescent indicators SBFI and BCECF, respectively. In addition, H+ secretion was assayed by the pH-stat method, and Na+ or Ca2+ fluxes were measured with 22Na or 45Ca, respectively. H+ secretion was significantly depressed by several experimental conditions that are known to inhibit the Na(+)-H+ antiporter: H+ secretion decreased 44% in the presence of 10(-5) M ethylisopropylamiloride, 49% in Na+o-free media, 44% in the presence of 10(-4) M ouabain, and 32% in the presence of 10(-4) M 8-bromoadenosine 3',5'-cyclic monophosphate. In addition, pHi decreased by 0.2 pH units in Na+o-free media. Finally, recovery from an intracellular acidosis evoked by 20 mM NH4Cl pulse required the presence of extracellular Na+. When the extracellular pH (pHo) was increased from 7.4 to 8.0, H+ secretion increased 58% from 17.5 to 27.7 nmol.min-1.mg protein-1 and Na+ influx increased 48%. As a result, pHi rose from 7.43 to 7.71 and Na+i increased from 15.6 to 19.7 mM. Finally, Ca2+i rose from 120 to 268 nM. These results suggest that the high pHo stimulated the Na(+)-H+ antiporter, and the subsequent rise in Na+i decreased the Na+ electrochemical potential, thereby activating the reverse mode of Na(+)-Ca2+ exchange (Ca2+ influx vs. Na+ efflux) which led to the rise in Ca2+i.(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonium Chloride↗
PubMed1990

Effects of low extracellular Ca2+ on cytosolic free Ca2+, Na+, and pH of MDCK cells.

The effects of lowering the Ca2+ electrochemical potential (delta mu Ca2+) by removing extracellular calcium (Ca2+o) was studied in Madin-Darby canine kidney (MDCK) cells. We measured cytosolic free calcium (Ca2+i), intracellular Na+ (Na+i), and intracellular pH (pHi) as well as Ca2+ and Na+ influx and efflux and H+ secretion. As soon as Ca2+o was lowered to zero, Ca2+ efflux increased 2-fold, and Na+ influx increased 4.3-fold. As a result, Ca2+i fell 71% from 120 to 34.7 nM, and Na+i rose 56% from 16.7 to 26.1 mM. At the same time, H+ secretion was depressed 38%, and pHi fell from 7.32 to 7.22. When Ca2+o was restored to normal (1.3 mM), there was a sharp rise in Ca2+i from 34.7 to 243 nM (+600%) caused by an immediate increase in Ca2+ influx (+112%). At the same time, Na+ efflux increased 20%. Ten to fifteen minutes after restoring Ca2+o to 1.3 mM, Ca2+i, Na+i, and pHi were back to control levels. These results suggest that reducing delta mu Ca2+ activates the forward mode of Na(+)-Ca2+ exchange which leads to a fall in Ca2+i and a decreased delta mu Na+ by increasing Na+i. The fall in delta mu Na+ secondarily depresses Na(+)-H+ exchange which results in a reduced H+ secretion and a fall in pHi. When Ca2+o is restored to 1.3 mM, the reverse mode of Na(+)-Ca2+ exchange is activated, since delta mu Ca2+ is larger than normal because of the low Ca2+i, and delta mu Na+ is reduced because of the high Na+i.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Coincidence of risk factors and early carotid lesions, detected with modern ultrasound techniques.

Using a multichannel pulsed Doppler ultrasound device, studies of flow kinetics and vessel wall motility at the beginning of the internal carotid artery (ICA) were carried out. Regarding the results of special computer analysis in 120 subjects with healthy vessels, a dilation of the proximal ICA and a decrease in mean flow velocity which was related to the age of the individual could be assessed. Depending on age and risk factors, wall dyskinetics and turbulences in the dorso-lateral part of the vessel could be detected and confirmed by the flow imaging method. In a second study of 100 subjects (between 15 and 50 years of age) without risk factors, an age-dependent dilatation of ICA could be diagnosed by high resolution Duplex system. In the same study an increased incidence of wall thickening and plaques formation in the dilated area of the ICA was observed. The study of 234 patients with different risk factors showed that hypertonics developed an extended dilatation of the ICA and that wall thickening and plaque formation occurred significantly more often than in other risk groups.

Adult↗
PubMed1986

Rural health promotion: bailiwick for social work.

A variety of factors have prompted increasing interest in prevention in health care practice in this country. In describing a rural health promotion project in which a social worker played a key role, this article illustrates how social work practitioners can bring their many skills to bear in efforts to promote health.

Community Health Services↗