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Biomedical subjects

A R Martin

Publications and source records attributed to A R Martin.

At least 109 records · Page 6Linked to original sources
PubMed1970

Effects of iontophoretically applied drugs on spinal interneurons of the lamprey.

1. Intracellular records were obtained from giant interneurones in the isolated spinal cord of the sea lamprey. The cells had a mean resting potential of about 75 mV and action potentials with overshoots of about 35 mV. Their input resistances, measured by passing polarizing currents through the recording pipette, were in the range 3-7 MOmega.2. Iontophoretic ejection of gamma-aminobutyric acid (GABA) from a micropipette placed near the surface of a cell resulted in a slight hyperpolarization, accompanied by a marked reduction in input resistance. The reversal point for the potential change was about 5 mV greater than the resting membrane potential.3. Iontophoretic application of L-glutamate to the cells produced a depolarization with a decrease in input resistance much smaller than that accompanying a GABA potential of similar amplitude. The action potential amplitude was reduced by L-glutamate application. The reversal potential could not be determined accurately but appeared to be near zero membrane potential.4. Glutamate application produced, in addition, a burst of inhibitory synaptic potentials in the cell, presumably by depolarizing either inhibitory presynaptic nerve terminals or nearby inhibitory cell bodies.5. Acetylcholine (ACh) produced no detectable change in membrane resistance or potential.6. Application of the three drugs to first-order sensory cells in the spinal cord had no effect on their membrane properties.

Acetylcholine↗
PubMed1970

Estimates of probability of transmitter release at the mammalian neuromuscular junction.

1. Intracellular records of end-plate potentials (e.p.p.s) were obtained from curarized neuromuscular junctions in the rat diaphragm.2. Statistical estimates of the quantal release probability (p) were made at individual junctions from measurements of the means and variances of e.p.p. amplitudes at two different levels of Ca concentration. It was assumed that the release process was binomial and that the number of quanta available for release (n) was independent of external Ca.3. These estimates of p were compared with those obtained by measuring depression of e.p.p. amplitudes after single conditioning shocks and assuming that the depression was due to depletion of n. The statistical estimates were consistently smaller.4. This disparity, plus the additional observation that depression was not linearly related to the number of quanta released by one or more conditioning shocks, suggested that depression was not due entirely to depletion and that the depletion assumption led to an over-estimate of p.5. A third method of estimating p from measurements of the decline of e.p.p. amplitudes during rapid stimulation also appeared to result in an over-estimate.

Animals↗
PubMed1969

Report of the 1966-67 cholera vaccine field trial in rural East Pakistan. I. Study design and results of the first year of observation.

A controlled cholera vaccine field trial was carried out in rural East Pakistan during the 1966-67 cholera season. A commercial cholera vaccine of average potency was tested in 40 000 children aged 3 months to 14 years in 1- and 2-dose schedules. In the cholera season extending for 8 months following immunization, a single dose produced an over-all protection of 46%; 2 doses at an interval of 1 month provided 64% protection. The single dose was virtually ineffective in children under 5 years, but provided significant protection in older children. The enhanced effect of the 2-dose schedule was primarily due to the boosting of protection in children under the age of 5 years. The duration of significant protection, even with the 2-dose schedule, did not appear to extend beyond the first 3 months of the 8-month cholera season.

Adolescent↗
PubMed1968

A note on transmembrane potential in dermal melanophores of the frog and movement of melanin granules.

1. Transmembrane potentials were measured and distribution of melanin granules observed in dermal melanophores of the isolated frog's web.2. In normal Ringer solution, melanin granules were aggregated in the cell bodies and the transmembrane potentials were usually in the range 70-90 mV.3. Addition of alpha-melanocyte stimulating hormone (alpha-MSH) to the bathing solution resulted in dispersion of the melanin granules into the processes of the cells, without any accompanying change in membrane potentials. Altering the membrane potentials by changing the external K(+) concentration had no effect on melanin migration.4. It is concluded that migration of melanin granules in these cells is unrelated to cell membrane polarization.

Animals↗
PubMed1968

The relation between quantum content and facilitation at the neuromuscular junction of the frog.

1. Experiments were done on the neuromuscular junction of the frog to study facilitation of the end-plate potential (e.p.p.) produced by one or more conditioning shocks applied to the motor nerve. Neuromuscular transmission was blocked with Mg (+)-tubocurarine chloride.2. In Mg-blocked preparations, facilitation increased with increasing Mg concentrations in the range 14-34 mM. The increase in facilitation was related specifically to the decrease in mean quantum content of the e.p.p., and was most marked with quantum contents less than 10.3. Facilitation in curarized preparations was similar in magnitude to that in preparations blocked with the lower Mg concentrations. Interaction between facilitation and depression in curarized preparations was consistent with the idea that facilitation was due to an increase in probability of transmitter release and depression to depletion of transmitter.

Animals↗