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Biomedical subjects

D L Cook

Publications and source records attributed to D L Cook.

At least 55 records · Page 3Linked to original sources
PubMed1987

A quantitative method for the detection and localization of quantum-limited events from radionuclides in cells and tissue sections by computer-enhanced video microscopy.

Cellular dynamics often involve extremely low concentrations of biologically active substances, which can be radiolabeled and detected, localized and quantitated by autoradiography. The latter may require exposures from a few days to many months. The objective of this research was to demonstrate the feasibility of reducing this long period of data collection by one to two orders of magnitude, while maintaining or improving the spatial resolution and localization in tissues and the quantitative characteristics inherent in autoradiography. A mathematical model describing the complete system was generated using energy partition calculations to estimate photon production via scintillant per H3 beta particle emission and to estimate the subsequent photon capture based upon imaging system parameters and microscope geometry. Calculations showed that, typically, a single tritium beta particle produces a maximum of 5.8 X 10(3) photons. A photon-limited camera and microscope imaging system were selected and optimized in conjunction with a specially developed physical scintillation model. Results showed that the number of detected photoevents increases monotonically with both signal integration time and, independently, with the concentration of the radionuclide. Consequently, this work demonstrates that video microscopy imaging methods can spatially and temporally quantify very low concentrations of radiolabeled substances and can reduce data acquisition times.

Beta Particles↗
PubMed1986

Induction of estrus in ovariectomized cows and heifers: effects of estradiol benzoate and gonadotropin releasing hormone.

Three experiments were conducted with ovariectomized (OVX) cows and heifers to investigate potential neuroendocrine mechanisms controlling estrous behavior. In Exp. 1, 10 OVX cows were treated with either 125 micrograms estradiol benzoate and 10 cc saline (125 micrograms EB + SAL), 125 micrograms EB and 500 micrograms gonadotropin releasing hormone (125 micrograms EB + GnRH), 250 micrograms EB and 10 cc SAL (250 micrograms EB + SAL), 250 micrograms EB and 500 micrograms GnRH (250 micrograms EB + GnRH) or 500 micrograms EB and 10 cc SAL (500 micrograms EB + SAL) in a replicated 5 X 5 Latin-square design. During the 48 h following EB injection, 2-h observation blocks were alternated with 2-h non-observation blocks. During each 2-h observation block, 14 behavioral interactions were monitored. The percentage of cows in estrus was lower for cows receiving 125 micrograms EB as compared with those given the higher doses. However, the cows receiving 125 micrograms EB + SAL did not differ in their estrous response from those receiving 125 micrograms EB + GnRH. The interval from injection to the onset of estrus and the duration of estrus were similar for all treatments. In Exp. 2, 10 OVX heifers were subjected to the same treatments and observation procedures utilized in Exp. 1. The results of Exp. 2 were similar to those of Exp. 1. In Exp. 3, 10 OVX cows were treated with either 300, 600, 1,200, 2,400 or 4,800 micrograms EB in a replicated 5 X 5 Latin-square design.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

The sulphonylurea receptor may be an ATP-sensitive potassium channel.

The stimulation of insulin secretion from the beta cells of the islets of Langerhans appears to be mediated by a decrease in the cell-membrane potassium-ion permeability. Tolbutamide reduced K+ movement through an ATP-sensitive K+ channel in patches of plasma membrane from an insulin-producing cell line when applied to the external surface of the membrane. The effect occurred at concentrations which exist in the serum of patients treated with tolbutamide and which stimulate insulin secretion from islets of Langerhans in vitro. Glibenclamide had a similar effect but, in keeping with its greater therapeutic potency, at concentrations one hundred times lower. These findings suggest that an ATP-sensitive K+ channel or a protein closely associated with it may be the receptor through which sulphonylureas act to stimulate insulin secretion in vitro.

Adenosine Triphosphate↗
PubMed1985

Voltage-gated Ca2+ current in pancreatic B-cells.

Voltage-dependent inward Ba++ and Ca++ currents were recorded in cultured neonatal rat pancreatic islet cells using the whole-cell voltage clamp technique. Outward current was suppressed by internal Cs+ and ATP and external TEA. Inward currents activated rapidly and decayed to a variable extent. The current decay was particularly marked when using long duration or large depolarizing pulses. Currents were due to Ca++ channel activation since they were abolished by omitting Ba++ and Ca++ or including Co++.

Animals↗
PubMed1984

Glucagon and forskolin have dual effects upon islet cell electrical activity.

We have investigated the effects of glucagon and forskolin upon pancreatic islet cell electrical activity using intracellular recordings from single mouse islets. Glucagon (0.1-2.0 microM) and forskolin (0.5-5.0 microM), both adenylate cyclase activators, potentiated glucose (200 mg/dl)-induced electrical activity. In the steady-state, islet cells have cyclic electrical activity with periodically recurring "plateau" depolarizations (with superimposed Ca++ action potentials) separated by silent hyperpolarizations. Both glucagon and forskolin mimicked glucose stimulation by increasing the fraction of each cycle spent in the plateau phase (the "plateau fraction"). Unlike glucose, however, glucagon and forskolin increased, rather than decreased, the overall frequency of plateaus, suggesting that plateau frequency is not tightly linked to changes of plateau fraction. This dissociation was also apparent during the onset of drug action. Plateau fraction increased immediately (within one minute), fell to a nadir and then rose to a new steady state level. Plateau frequency, however, rose slowly and monotonically to a new level. Following drug withdrawal plateau fraction returned to control levels several minutes before plateau fraction. From these results it was concluded that cAMP has two effects upon islet cell electrical activity: one is to increase plateau fraction possibly by stimulating glucose-dependent process, which results in increasing in Ca++ influx, and the other to increase plateau frequency possibly by reducing intracellular Ca++ buffering.

Action Potentials↗
PubMed1984

Rat islet cells have glucose-dependent periodic electrical activity.

In order to examine whether rat islet cells have a glucose-dependent plateau/silent phase pattern of electrical activity as seen in mouse islets, intracellular recordings were made in cultured whole rat islets. Rat islet cells responded to glucose stimulation with membrane potential alterations between a polarized silent phase and a depolarized plateau phase associated with spikes. Increasing or decreasing glucose stimulation prolonged or shortened the relative duration of plateau phase, respectively. Removal of glucose from the medium caused membrane hyperpolarization with disappearance of electrical activity while reintroduction of glucose caused membrane depolarization and biphasic onset of electrical activity. These results indicate that rat islet cells have a glucose dependent plateau/silent phase electrical mechanism nearly identical to that seen in mouse islets.

Animals↗
PubMed1984

Electrical pacemaker mechanisms of pancreatic islet cells.

Glucose, the major physiological stimulus for insulin secretion, induces a periodic bursting pattern of Ca2+ action potentials that are thought to mediate the uptake of Ca2+ into the intracellular pool of free Ca2+, which controls the rate of insulin release. Evidence is reviewed that shows that the voltage-dependent Ca2+ spikes are driven by a slow, voltage-dependent plateau depolarization that may also be caused by Ca2+ influx. Current evidence suggests that this plateau conductance is periodically terminated in turn by a pacemaker current through membrane K+ channels that are activated by intracellular free Ca2+. The control of electrical activity by different modulators of insulin release may involve interactions with this system at several points, including changes of the sensitivity of K+ channels to intracellular Ca2+ and to changes of intracellular Ca2+ buffering capacity.

Acetylcholine↗
PubMed1983

Isolated islets of Langerhans have slow oscillations of electrical activity.

Glucose-induced membrane electrical activity was recorded from single isolated mouse islets of Langerhans exposed to steady levels or to step changes of glucose concentration. Superimposed on the well-known rapid (approximately 15-second period) alternations in membrane potential, slow oscillations in the intensity of the electrical activity were observed having a period of 4.6 +/- 0.2 minute (mean +/- SEM, n = 19 islets) and a range of 3.0-6.2 minutes. The largest observed amplitude of oscillation was nearly 50% of the mean intensity. In 62 consecutive recordings from different islets, eleven (18%) islets oscillated steadily after 10 minutes of constant bath conditions while an additional eight islets (13%) oscillated only transiently following abrupt changes of islet stimulation. The oscillations, when triggered by changes of islet stimulation, appeared to be a "ringing" of the biphasic kinetics previously described for both electrical activity and insulin release. Since glucose-induced electrical activity is known to be well correlated with insulin secretory rate, these observations suggest that single isolated mouse islets may also display periodic insulin secretion.

Animals↗
PubMed1982

Islet electrical pacemaker response to alpha-adrenergic stimulation.

To characterize the pancreatic islet cell responses to adrenergic stimulation, membrane potentials have been recorded from isolated, perifused mouse islets of Langerhans exposed to a steady glucose level of 200 mg/dl. Various doses of epinephrine HCl from 5 to 10,000 nM have been applied for 10--15-min test periods separated by 10--15-min control periods. Epinephrine produced a dose-dependent suppression of glucose-induced membrane electrical activity. Adding epinephrine (50--100 nM) reduced the plateau fraction (the fraction of each plateau/silent phase cycle spent in the plateau phase) from 0.41 +/- 0.03 (X +/- SEM, N = 13) to 0.28 +/- 0.08 (N = 5, P = 0.05) and more markedly reduced the plateau frequency from 2.56 +/- 0.32 (N = 13) to 0.80 +/- 0.23 min-1 (N = 5, P less than 0.02). Adding 10- and 100-fold higher concentrations of epinephrine had little additional effect. There was no effect of epinephrine on the membrane potential levels of the plateau and silent phase after a new steady state was achieved and no effect on the amplitude and waveform of the rapid spikes. The pattern of inhibition of the plateau/silent phase cycles by epinephrine is qualitatively different from the pattern seen during inhibition of electrical activity by reducing glucose level. This suggests that the electrical rhythm is controlled by more than one pathway. The persistence of electrical activity at very high levels of epinephrine (to 10,000 nM) suggests that electrical activity and, therefore, Ca2+ uptake can exist in the absence of insulin release.

Animals↗
PubMed1981

Voltage dependence of rhythmic plateau potentials of pancreatic islet cells.

The origin and control of glucose-induced rhythmic plateau potentials of pancreatic islet cells have been studied with intracellular microelectrodes in isolated mouse islets. Rapid changes of extracellular potassium concentration and direct electrical stimulation via a suction electrode were used to perturb islet cell membrane potentials. We show that brief depolarizing stimuli trigger permature plateau potentials, and brief hyperpolarizing currents abort endogenous plateaus. Both responses occur in an all-or-none manner, show a reciprocal relationship between stimulus strength and stimulus duration, have stimulus thresholds that approach zero at the time of the endogenous event, and completely reset the endogenous plateau rhythm. These results indicate that the plateau potentials are due to voltage-dependent regenerative mechanisms as in other electrically excitable tissues and implicate membrane potential or membrane ionic fluxes in the glucose-dependent pacemaker system that triggers their onset and offset.

Action Potentials↗
PubMed1981

Glucose and acetylcholine have different effects on the plateau pacemaker of pancreatic islet cells.

Pancreatic islet cell membrane electrical activity has been studied with intracellular microelectrodes in perifused, isolated mouse islets of Langerhans. The dose-response effects of glucose and of acetylcholine on the pattern of electrical activity are compared and are shown to be qualitatively different. Electrical activity in the presence of glucose consists of periodic alterations between a polarized silent phase potential and depolarized plateau phase with superimposed rapid spiking activity. Increasing glucose concentration prolongs the plateau phase, at the expense of the silent phase, and thus increases the the plateau fraction (the fraction of time in each electrical cycle spent in the plateau phase). By contrast, graded doses of acetylcholine, in the presence of stimulatory levels of glucose, had no effect on plateau fraction. Increasing glucose concentration also slightly reduced the frequency of plateaus, whereas increasing acetylcholine markedly increased plateau frequency. Furthermore, changes of glucose concentration had no effect on the potential levels during the plateau and silent phases, while addition of acetylcholine depolarized the silent phase until, at high concentrations of acetylcholine, the combination of increased plateau frequency and silent phase depolarization produced continuous spiking. Addition of acetylcholine to a slightly substimulatory level of glucose depolarized the membrane without, however, inducing periodic spiking activity. The results suggest aht the effects of acetylcholine and glucose are due to different effects on the plateau pacemaker system involved in the regulation of insulin release.

Acetylcholine↗
PubMed1981

Intakes of vitamins and minerals by pregnant women with selected clinical symptoms.

Toxemia in pregnancy is characterized by a combination of at least two of the following clinical symptoms: hypertension, edema, and proteinuria. In this study the dietary intakes of young pregnant women attending a Maternal and Infant Care Program at Tuskegee Institute were evaluated for selected vitamins and minerals. Women with toxemia were identified, and women without toxemia served as controls. The toxemia group generally consumed lesser amounts of vitamins and minerals than the controls. However, both groups were deficient (less than two-thirds RDA) in calcium, magnesium, vitamin B6, vitamin B12, and thiamin. Milk, meat, and grains supplied an appreciable proportion of each vitamin except vitamin A, which was found primarily in the two vegetable groups. Meat and grains contained the greatest quantities of minerals, but milk provided a relatively good proportion of potassium, calcium, magnesium, and phosphorus. Anemia was not related to the incidence of toxemia. Women exhibiting anemia consumed smaller amounts of vitamins studied than did women without anemia.

Diet↗
PubMed1976

A continuous-flow, variable mixing valve for perfusion experiments.

The device described here continuously mixes two solutions in any required ratio and has been used at flow rates of 6 ml/min in tissue perfusion experiments. Its low-cost construction consists of a three-way miniature solenoid valve driven by a simple electronic circuit. Mixing is stable, reproducible and accurate to +/- 1% of dial setting.

Electronics, Medical↗