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Biomedical subjects

A D Carlson

Publications and source records attributed to A D Carlson.

8 recordsLinked to original sources
PubMed1977

Ionic basis of axonal excitability in an extreme euryhaline osmoconformer, the serpulid worm Mercierella enigmatica (Fauvel).

Despite the extreme fluctuations in blood concentration experienced by this marine osmoconformer, essentially 'conventional' ionic mechanisms are involved in conduction by the giant axons in isosmotic conditions. The resting axonal membrane approximates to an ideal potassium electrode, with a 58-8 mV slope for decade change in [K+]O above 10 mM. The action potential overshoot shows a 55-8 mV decline with decade reduction in [Na+]O and the action potentials are blocked by tetrodotoxin at around 5 X 10(-7) M. The rising phase and overshoot of the action potential remain constant at potassium concentrations up to the relatively high level of 30 mM found in the blood, indicating an unusual absence of sodium inactivation over a wide range of resting potentials. Relatively rapid, symmetrical movement of potassium ions between the bathing medium and the axon surface is deduced from the potential changes induced by alterations in [K+]O. Outward movement of sodium ions (t0-5 = 33-5 s) occurs at a similar rate to that of potassium, but inward movement of Na+ is relatively slow and complex. It is concluded that the ability of axons to function in dilute media must involve specific adaptations to osmotic and ionic stress.

Action Potentials↗
PubMed1976

Octopamine: presence in firefly lantern suggests a transmitter role.

The lantern of the adult firefly is innervated by a nerve supply with endings similar to other known monoaminergic nerves. However, catecholamines could not be detected in the nerve endings and noradrenaline and adrenaline were relatively weak agonists in eliciting a flash of light when applied to the lantern in vitro. Firefly lanterns were assayed for octopamine using a sensitive, specific enzymatic assay in which octopamine is enzymatically converted to 3H-synephrine and quantitated by liquid scintillation counting. The presence of substantial amounts (125 ng/g tissue) of octopamine was demonstrated and confirmed by thin layer chromatography. On the basis of this and earlier work, it is suggested that the nerves to the firefly lantern are octopaminergic.

Animals↗