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At least 1,027 records · Page 57Linked to original sources
PubMed1966

The entry of sodium into human red blood cells in vivo.

The kinetics of sodium, movement into human red blood cells has been studied in vivo with (24)Na. When human serum albumin(-131)I is used to measure the percentage of plasma trapped in the packed red blood cells after centrifugation, approximately 30 % of red blood cell sodium is found to equilibrate immediately with plasma. It is concluded that this immediately exchangeable compartment of red blood cell sodium is an experimental artefact, associated with the use of labeled albumin for measuring plasma trapping. This immediately exchangeable fraction disappears when sucrose-(14)C is used to measure plasma trapping. The experimental results were examined by compartmental analysis, using an analogue computer. The results obtained, when plasma trapping was measured with sucrose-(14)C could be simulated by the use of models containing two compartments, arranged in series or in parallel. The errors of the techniques used and the possible physical basis for the results are discussed.

Carbon Isotopes↗
PubMed1968

A kinetic model for the action of xylocaine on receptors for acetylcholine.

A kinetic scheme postulating the rapid formation of a partially active acetylcholine-receptor-drug complex from Xylocaine (or a derivative) and the active acetylcholine-receptor complex can account for the effects of Xylocaine and its derivatives at the neuromuscular junction. Transmembrane currents generated by an analogue computer programmed according to the scheme can exactly match end plate currents produced by nerve stimulation in the presence of the drugs. The scheme also accounts for the qualitatively different effects of the drugs on the end plate potential and on responses to iontophoretically applied acetylcholine. The analysis presented is consistent with very rapid reactions between acetylcholine and receptors, characterized by rate coefficients in the range 10(4) to 10(6) sec(-1). It is based on the hypothesis that the activation of receptors by acetylcholine changes the structure of the receptors and thus their affinity for Xylocaine. The analysis does not require pharmacological separability of sodium and potassium conductances during the end plate current.

Acetylcholine↗
PubMed1970

Cellular inhomogeneity in dog red cells as revealed by sodium flux.

Unidirectional (24)Na fluxes across the dog red blood cell membrane were measured. The kinetics were incompatible with a single time constant but could be accounted for in terms of a two-series compartment cell model, with approximately 1% of cell Na in the outer compartment. Dog red blood cells are known to be inhomogeneous in their Na and K permeabilities. Theoretical analysis showed that such cellular inhomogeneity in the Na permeability coefficient might in principle account for the flux data. In order to evaluate the inhomogeneity effect, a technique based on the differential response of cells suspended in isosmolar high K buffers was devised to measure the variations in Na permeability in the cell population. A variation in the Na permeability coefficient of approximately 30% was found. This inhomogeneity is insufficient to account for the flux data.

Animals↗
PubMed1973

An analysis of hamster afferent taste nerve response functions.

Sensitivities to moderately intense stimuli representing four taste qualities to man were determined for 79 hamster chorda tympani fibers. Some fibers were very sensitive to sucrose, sodium chloride, or hydrochloric acid, but none were very sensitive to quinine. These sensitivities were not randomly distributed among fibers: the sucrose sensitivity was separated from and negatively correlated with the other sensitivities which were associated and positively correlated with each other. Moreover, there were a limited number of sensitivity patterns: (a) fibers responding best to sucrose responded second-best to salt, less to acid, not to quinine; (b) fibers responding best to salt either responded second-best to sucrose and not to acid or quinine; or second-best to acid, less to quinine, and not to sucrose; and (c) fibers responding best to acid responded second-best to salt, more to quinine, and less to sucrose than other fibers. Therefore, if four stimuli of different taste qualities are ordered from acceptable to unacceptable, neural response functions of most hamster chorda tympani taste fibers peak at one point. Sensitivities to nine other moderately intense stimuli which vary in quality to man were also determined for 46-49 of the fibers. Sensitivities to sweet stimuli were always associated with each other and separated from sensitivities to nonsweet stimuli. Sensitivities to nonsweet stimuli were all associated with each other; however, the strongest correlations were between sensitivities to stimuli of like quality, e.g., the three acids or the two sodium salts.

Animals↗
PubMed1976

An improved vaseline gap voltage clamp for skeletal muscle fibers.

A Vaseline gap potentiometric recording and voltage clamp method is developed for frog skeletal muscle fibers. The method is based on the Frankenhaeuser-Dodge voltage clamp for myelinated nerve with modifications to improve the frequency response, to compensate for external series resistance, and to compensate for the complex impedance of the current-passing pathway. Fragments of single muscle fibers are plucked from the semitendinosus muscle and mounted while depolarized by a solution like CsF. After Vaseline seals are formed between fluid pools, the fiber ends are cut once again, the central region is rinsed with Ringer solution, and the feedback amplifiers are turned on. Errors in the potential and current records are assessed by direct measurements with microelectrodes. The passive properties of the preparation are simulated by the "disk" equivalent circuit for the transverse tubular system and the derived parameters are similar to previous measurements with microelectrodes. Action potentials at 5 degrees C are long because of the absence of delayed rectification. Their shape is approximately simulated by solving the disk model with sodium permeability in the surface and tubular membranes. Voltage clamp currents consist primarily of capacity currents and sodium currents. The peak inward sodium current density at 5 degrees C is 3.7 mA/cm2. At 5 degrees C the sodium currents are smoothly graded with increasing depolarization and free of notches suggesting good control of the surface membrane. At higher temperatures a small, late extra inward current appears for small depolarizations that has the properties expected for excitation in the transverse tubular system. Comparison of recorded currents with simulations shows that while the transverse tubular system has regenerative sodium currents, they are too small to make important errors in the total current recorded at the surface under voltage clamp at low temperature. The tubules are definitely not under voltage clamp control.

Action Potentials↗
PubMed1978

An analogue device for the measurement of cardiovascular variables.

An analogue device is described which is designed to analyse repetitive signals. It measures peak amplitudes, time to peak values, areas, and values at a preset time. The results can be displayed or recorded on a beat-to-beat basis, or an average can be taken over up to 31 consecutive beats.

Cardiovascular Physiological Phenomena↗