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Biomedical subjects

S Yeandle

Publications and source records attributed to S Yeandle.

11 recordsLinked to original sources
PubMed1991

Norepinephrine stimulates potassium efflux from pinealocytes: evidence for involvement of biochemical "AND" gate operated by calcium and adenosine 3',5'-monophosphate.

Biochemical studies of K+ efflux from rat pinealocytes revealed for the first time that norepinephrine (NE) increases 86Rb+ and 42K+ efflux. The effects of NE depend upon concurrent activation of both alpha 1- and beta-adrenoceptors. This effect is mediated by cAMP and Ca2+, which appear to act in conjunction to control K+ efflux; studies with charybdotoxin and tetraethylammonium indicate that a Ca2(+)-sensitive K+ channel (K(Ca] appears to be involved. Patch clamp studies identified a large conductance (approximately 100 psec) K+ channel. This study also revealed for the first time that NE treatment increases the fraction of time that this channel was open. Studies of inside-out pineal membrane patches indicated that increasing Ca2+ at the cytoplasmic surface of the membrane increased the frequency of channel opening, as is typical of K(Ca) channels in this type of preparation. Outward K+ currents were almost completely blocked by tetraethylammonium (10 mM) and scorpion venom (L. quinquestriatum; 100 ng/ml). Cell-attached studies confirm that the effects of NE are mediated by intracellular second messengers. These investigations suggest that NE elevates K+ flux, probably through a large conductance K(Ca) channel, that NE acts through alpha 1- and beta-adrenergic receptors, and that Ca2+ and cAMP act together through a biochemical "AND" gate to mediate the effects of receptor activation. Activation of this K(Ca) channel would have a hyperpolarizing influence and might contribute to the adrenergic hyperpolarization of pinealocytes.

Animals↗
PubMed1985

The effect of electrical current on the healing of mandibular freeze-dried bone allografts in dogs.

Low levels of electrical current have been shown to affect the process of osseous repair. This study experimentally evaluated the effect of electrical stimulation on the healing of freeze-dried mandibular allogeneic bone grafts in dogs. Healing of the grafts was monitored by sequential submento-occlusal radiographs and radionuclide bone imaging at two, four, six, and eight weeks after grafting. Results indicated no significant difference in the osseous repair of stimulated and nonstimulated freeze-dried allogeneic bone grafts.

Animals↗
PubMed1985

Statistics and quantum bumps in arthropod photoreceptors.

Discrete waves of depolarizing membrane potential in arthropod photoreceptors, called quantum bumps, appear to result from single-photon absorptions of the visual pigment. Statistical analysis of bump records suggest a model for bump occurrence in dark-adapted receptors at low levels of illumination. This model assumes that a photon that isomerizes a visual pigment molecule can trigger a stochastic process that can produce no more than one bump under normal conditions, and that the stochastic processes triggered by different isomerized visual pigment molecules are independent of each other.

Animals↗
PubMed1977

Neuromuscular transmission in the frog at 31 ATA helium pressure.

Synaptic potentials were recorded extracellularly in in vitro frog cutaneous pectoris nerve muscle preparation in air at 1 ATA and in a hyperbaric gas environment of 1 ATA air plus 30 ATA helium. Sufficient curare was always used in the bathing solution to prevent propagated muscle action potentials upon maximal stimulation of the nerve. Shape of the synaptic potential and poststimulus facilitation and depression were compared in these two environments. No significant differences were found.

Air↗
PubMed1974

Independence of location of light absorption and discrete wave latency distribution in Limulus ventral nerve photoreceptors.

Discrete waves of depolarization evoked by dim pulses of light in dark-adapted ventral nerve photoreceptors in Limulus show fluctuation in their latency. To a resolution of 5-10 microm the latency distribution function appears to be independent of where in the receptor light is absorbed. Also, there is apparent local adaptation to bright light pulses.

Adaptation, Ocular↗
PubMed1973

Light-evoked and spontaneous discrete waves in the ventral nerve photoreceptor of Limulus.

Discrete waves, recorded from the ventral nerve photoreceptor, occur in the light and in the dark. Spontaneous waves, on the average, are smaller than light-evoked waves. This suggests that not all spontaneous waves can arise from spontaneous changes in the visual pigment molecule identical to changes induced by photon absorption. Spontaneous and light-evoked waves are statistically independent of each other. This is shown by determination of frequency of response as a function of pulse energy for short pulses and determination of the distribution of intervals between waves evoked by steady lights. The available data can be explained by two models. In the first each photon produces a time-dependent excitation that goes to zero the instant the wave occurs so that the number of effective absorptions from a short light pulse equals the number of waves produced by the light pulse. In the second the excitation produced by photon absorption is unaffected by the occurrence of the waves so that the number of waves produced from a short light pulse may be different from the number of effective absorptions. Present results do not allow a choice between the two models.

Animals↗
PubMed1970

Stochastic properties of discrete waves of the limulus photoreceptor.

In the dark-adapted photoreceptor of the horseshoe crab, Limulus, transient discrete depolarizations of the cell membrane, discrete waves, occur in total darkness and their rate of occurrence is increased by illumination. The individual latencies of the discrete waves evoked by a light stimulus often cannot be resolved because the discrete waves overlap in time. The latency of the first discrete wave that follows a stimulus can be determined with reasonable accuracy. We propose a model which allows us to make an estimate of the distribution of the latencies of the individual light-evoked discrete waves, and to predict the latency distribution of the first discrete wave that follows a stimulus of arbitrary intensity-time course from the latency distribution of the first discrete wave that follows a brief flash of light. For low intensity stimuli, the predictions agree well with the observations. We define a response as the occurrence of one or more discrete waves following a stimulus. The distribution of the peak amplitudes of responses suggests that the peak amplitude of individual discrete waves sometimes has a bimodal distribution. The latencies of the two types of discrete waves, however, follow similar distributions. The area under the voltage-time curve of responses that follow equal energy long (1.25 sec) and short (10 msec) light stimuli follows similar distributions, and this suggests that discrete waves summate linearly.

Animals↗
PubMedDate not supplied

Electrically quiet temperature controller.

A circuit for an electrically quiet temperature controller is described that is suitable for controlling the temperature of a neurophysiological preparation above ambient temperature. By not generating spurious electrical signals it facilitates the recording of low level biological potential changes when temperature control is required. The device, constructed of standard electronic components, uses a thermistor as a sensing element and an ordinary heat lamp or heating strip as a heating element.

Animals↗
PubMedDate not supplied

An inexpensive electronic switch for preventing amplifier overload in neurophysiological recording.

A circuit for an electronic switch is described that suppresses large unwanted signals that might overload physiological amplifiers during recording of weak neural signals. The circuit, made from inexpensive and easily available integrated circuits, can be operated from any timer that produces at least a +5 volt output pulse. It operates by connecting a low gain preamplifier to a high gain amplifier only during the signal of interest.

Amplifiers, Electronic↗