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Biomedical subjects

A R Martin

Publications and source records attributed to A R Martin.

At least 73 records · Page 4Linked to original sources
PubMed1981

The computation of simulated endplate potentials.

A method is described for computing simulated subthreshold responses (.e. endplate potentials) for the Falk-Fatt (1964) cable model of a muscle fibre due to a punctate change in ionic conductance. The method has been applied to a comparison of the Falk-Fatt and classical models. Comparison with experimental results suggests that the model is adequate to account for the response of the mouse muscle fibre, in which the endplate is highly localized. For frog muscle there are larger discrepancies, which may be due to the extended endplate in this species.

Animals↗
PubMed1981

Non-linear summation of end-plate potentials in the frog and mouse.

1. End-plate potentials (e.p.p.s) and end-plate currents (e.p.c.s) were recorded intracellularly from muscle fibres of frog and mouse at various levels of curarization to determine the relation between the potential change and the underlying synaptic conductance change over a wide range of e.p.p. amplitudes. 2. In frog muscle fibres the e.p.p.-e.p.c. relation was linear for e.p.p. amplitudes up to about 10 mV, beyond which the rate of increase of e.p.p. amplitude became progressively smaller as the e.p.c. amplitude increased. The equation proposed by Martin (1955) to correct for this non-linearity consistently over-corrected the e.p.p. amplitudes. 3. When synaptic potentials and currents of long duration were produced by ionophoresis of ACh onto the end-plate, the voltage-current relation showed greater non-linearity than with nerve-evoked responses, and correction of the synaptic potential amplitudes resulted in a linear relation. 4. The relation between e.p.p. and e.p.c. amplitudes in mouse muscle showed a greater non-linearity than in frog muscle and over-correction by the equation was correspondingly smaller. Theoretical voltage-current relations were calculated for various membrane models and compared with the relations observed experimentally. The results from mouse muscle agreed with those expected for a point synaptic contact on an infinite cable; those from from muscle were consistent with simple resistive-capacitative model with no cable extending from the synaptic region. 6. The applicability to the experimental results of several correction factors for non-linear summation is discussed.

Acetylcholine↗
PubMed1980

A trial of two strategies to modify the test-ordering behavior of medical residents.

We studied two methods to reduce the ordering of laboratory and radiologic tests by medical residents in their first postgraduate year. Dividing the residents into three groups, we compared the effect of concurrent chart review and discussion in one group with the effect of a moderate financial incentive for limited ordering of tests in a second group. The third group of residents served as a concurrent control, and data on the testing patterns of residents at the same hospital during the year before the study provided a retrospective control.

Boston↗
PubMed1980

Conformationally restricted phenothiazine neuroleptics. 1. 3-(Dimethylamino)-1,2,3,4-tetrahydroazepino[3,2,1-kl]phenothiazine.

A rigid analogue of promazine, 3-(dimethylamino)-1,2,3,4-tetrahydroazepino[3,2,1-kl]phenothiazine (1), was prepared by reductive amination of the corresponding ketone 4. An X-ray crystallographic study revealed that the seven-membered ring of the hydrochloride salt of 1 exists as a half-chair-like form with the dimethylammonium group in an equatorial-like conformation. Compound 1 was approximately one-half as active as promazine as an inhibitor of [3H]spiperone binding in rat corpus striatal homogenates. In homogenates obtained from calf caudate tissue, however, 1 was only about one-twentieth as active as promazine as an inhibitor of [3H] spiperone binding. As a stimulator of homovanilic acid (HVA) synthesis in rat corpus striatum in vivo, it was about one-tenth as active as promazine.

Animals↗
PubMed1980

An electrophysiological study of the effects of ionophore A23187 on Nauphoeta salivary glands.

The ionophore A23187 produces a hyperpolarization of cockroach salivary gland cells in the presence or absence of added calcium ions. The effect is greater and more prolonged in the presence of calcium and is dependent on the external potassium ion concentration. It is proposed that the ionophore can increase the intracellular calcium ion concentration by an increase in influx from the external medium or by mobilization of intracellular calcium stores and that this results in an increase in the potassim permeability, thus producing a hyperpolarization.

Animals↗
PubMed1978

Substituted tetralins VI: Tentative assignment of absolute stereochemistry of 1-methyl-1-phenyl-1,2,3,4-tetrahydro-3-naphthoic acid and N,N,1-trimethyl-1-phenyl-1,2,3,4-tetrahydro-3-naphthylamine isomers.

The absolute configurations of the enantiomers of N,N,1-trimethyl-cis- and trans-1-phenyl-1,2,3,4-tetrahydro-3-naphthylamines (Ia and Ib) were assigned tentatively from the circular dichroism spectrum of a bridged ketone derived by cyclization of optically active 1-methyl-cis-1-phenyl-1,2,3,4-tetrahydro-3-naphthoic acid (IIa). Thus, (--)-IIa and the corresponding amine, (--)-Ia, were assigned the (2S, 4R)-configuration. Epimerization of (--)-IIa through its methyl ester yielded the trans-acid, (--)-IIb, which established the absolute configuration of (--)-IIb and the corresponding amine, (--)-Ib, as (2R, 4R).

Circular Dichroism↗
PubMed1977

Effect of acetylcholine on postjunctional membrane permeability in eel electroplaque.

Acetylcholine (ACh) was applied iontophoretically to the innervated face of isolated eel electroplaques while the membrane potential was being recorded intracellularly. At the resting potential (about -85 mV) application of the drug produced depolarizations (ACh potentials) of 20 mV or more which became smaller when the membrane was depolarized and reversed in polarity at about zero membrane potential. The reversal potential shifted in the negative direction when external Na+ was partially replaced by glucosamine. Increasing external K+ caused a shift of reversal potential in the positive direction. It was concluded that ACh increased the permeability of the postjunctional membrane to both ions. Replacement of Cl- by propionate had no effect on the reversal potential. In Na+-free solution containing glucosamine the reversal potential was positive to the resting potential, suggesting that ACh increased the permeability to glucosamine. Addition of Ca++ resulted in a still more positive reversal potential, indicating an increased permeability to Ca++ as well. Analysis of the results indicated that the increases in permeability of the postjunctional membrane to K+, Na+, Ca++, and glucosamine were in the ratios of approximately 1.0:0.9:0.7:0.2, respectively. With these permeability ratios, all of the observed shifts in reversal potential with changes in external ionic composition were predicted accurately by the constant field equation.

Acetylcholine↗
PubMed1976

Reversal of acetylcholine potentials in eel electroplaque.

Although the eel electroplaque is a major source of purified acetylcholine (ACh) receptor, the electrophysiological properties of the receptor have not been studied in detail. In particular, the reversal potential for the action of ACh on the postsynaptic membrane has not been measured directly. In order to obtain the reversal potential, ACh was applied iontophoretically from a micropipette onto the innervated membrane. The resulting depolarization (ACh potential) decreased in amplitude as the cell was depolarized, reached zero at a reversal potential of about -4 millivolts, and then reversed in sign as the inside of the cell was made increasingly more postive. The relation between ACh potential amplitude and membrane potential was nonlinear because of a decrease with depolarization of the peak conductance change produced by the drug.

Acetylcholine↗
PubMed1976

Reduction in acetylcholine sensitivity of axotomized ciliary ganglion cells.

1. Isolated cell clusters from ciliary ganglia of 3- to 4-day-old chickens were used to examine the electrical characteristics and sensitivity to iontophoretically applied acetylcholine (ACh) of normal cells and cells that had been axotomized on the day of hatching. 2. Resting potentials, input resistances and capacitances were the same in axotomized cells as in normal cells. These averaged about 70 mV, 165 Momega and 35 pF respectively. 3. Sensitivity to iontophoretically applied ACh was lower in axotomized cells than in normal cells by a factor of about 8. The rise times of the ACh potentials were the same in the two groups; indicating that the reduced sensitivity was not due to a diffusion barrier. 4. The slopes of the dose-reponse curves, plotted on a double-logarithmic scale, suggested that the co-operative action of two ACh molecules was involved in activating a post-synaptic conductance channel. This relation was unaltered by axotomy. 5. The estimated reversal potential for the action of ACh was unchanged after axotomy. 6. Cells in isolated clusters were similar to those in intact ganlia with respect to threshold depolarization, amplitude and time course of action potentials and ability to generate repetitive action potentials. There were no differences in these characteristics between normal and axotomized cells. 7. Cells in the isolated clusters had input resistances which were larger by a factor of 2-3 and capacitances that were smaller by a factor of about 2 than those of cells in intact ganglia. It is suggested that these differences were due to loss of initial segments of axons from the isolated cells. 8. Normal cells in the isolated clusters displayed spontaneous miniature synaptic potentials, indicating that synaptic integrity was maintained during the isolation procedure. As in intact ganglia, no spontaneous activity was observed in axotomized cells.

Acetylcholine↗
PubMed1975

Comparison of television and telephone for remote medical consultation.

Television and telephone communications were randomly used to compare their effectiveness in allowing consultation between a hospital-based physician and remote nurse practitioners. Visits using television for consultation averaged 50 minutes as compared with 40 minutes for telephone. This difference was caused by longer work-ups before the consultation, longer delays after it was requested, and longer consultations, themselves, on television. However, television consultations resulted in significantly fewer immediate referrals of patients to hospital physicians: 6 plus or minus 1 as compared to 12 plus or minus 1 per cent (mean plus or minus S.E.M) OF ALL TELEPHONE CONSULTATIONS (P SMALLER THAN 0.005). Although no overall difference in satisfaction was documented between the results of television and telephone consultations, participants preferred the former for medical decision making and cited it for allowing more social interaction than telephone. These findings suggest that television may have its greatest value in remote sites where the sense of isolation is great and the need to reduce long-distance referrals offsets the costs of the system.

Community Health Services↗