Acta physiologica Scandinavica
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Acta Physiol. Scand. · Dec 2005
Ion channel regulation of the dynamical instability of the resting membrane potential in saccular hair cells of the green frog (Rana esculenta).
We investigated the ion channel regulation of the resting membrane potential of hair cells with the aim to determine if the resting membrane potential is poised close to instability and thereby a potential cause of the spontaneous afferent spike activity. ⋯ Two intrinsic dynamical instabilities of V(m) are present in hair cells. One of these is observed as spontaneous voltage fluctuations by currents through K(IR), K(V) and h-channels in combination with a steady current through MET channels. The other instability shows as regenerative voltage changes involving Ca2+ and K(V) channels. The BK(Ca) channels prevent the spontaneous voltage fluctuations from activating the regenerative system.
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Acta Physiol. Scand. · Nov 2004
Partial reversal of conduction slowing during repetitive stimulation of single sympathetic efferents in human skin.
To describe and identify the function of a class of human C fibre with an unusual response to repetitive electrical stimulation. Other C fibres slow progressively at 2 Hz (type 1), reach a latency plateau (type 2) or hardly slow at all (type 3). ⋯ The distinctive activity-dependent slowing profiles of these type-4 sympathetic C units may help identification in vitro, and suggest that hyperpolarization-activated channels have a particularly prominent role in the axonal membrane.
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Acta Physiol. Scand. · Nov 2004
ReviewRed blood cell pH, the Bohr effect, and other oxygenation-linked phenomena in blood O2 and CO2 transport.
The discovery of the S-shaped O2 equilibrium curve and the Bohr effect in 1904 stimulated a fertile and continued research into respiratory functions of blood and allosteric mechanisms in haemoglobin (Hb). The Bohr effect (influence of pH/CO2 on Hb O2 affinity) and the reciprocal Haldane effect (influence of HbO2 saturation on H+/CO2 binding) originate in the Hb oxy-deoxy conformational change and allosteric interactions between O2 and H+/CO2 binding sites. In steady state, H+ is passively distributed across the vertebrate red blood cell (RBC) membrane, and intracellular pH (pHi) changes are related to changes in extracellular pH, Hb-O2 saturation and RBC organic phosphate content. ⋯ Blood O2 transport shows several adaptive changes during exposure to environmental hypoxia. The Bohr effect is involved via the respiratory alkalosis induced by hyperventilation, and also via the pHi change that results from modulation of RBC organic phosphate content. In teleost fish, beta-adrenergic activation of Na+/H+ exchange rapidly elevates pHi and O2 affinity, particularly under low O2 conditions.
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Acta Physiol. Scand. · Nov 2004
Effect of exogenous angiotensin II on renal tissue nitric oxide and intrarenal circulation in anaesthetized rats.
The renal medullary circulation is protected against depressor action of angiotensin II (Ang II) because of the opposed action of a vasodilator agent, possibly nitric oxide (NO). This possibility was evaluated by a simultaneous determination of the effect of exogenous Ang II on renal cortical and medullary tissue NO and on intrarenal circulation. ⋯ An absence of an increase in renal cortical or medullary tissue NO after infusion of subpressor or pressor doses of Ang II speaks against the role of this agent in buffering the intrarenal vasoconstrictor action of the hormone. Elimination of the post-Ang II decrease in medullary NO in animals pre-treated with tempol suggests that tissue superoxide generation stimulated by the hormone might reduce local bioavailability of NO.
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Acta Physiol. Scand. · Oct 2004
Evaluation of a triple sugar test of colonic permeability in humans.
Conventional dual sugar tests of intestinal permeability assess only the stomach and small intestine. A novel triple sugar method of assessing colonic permeability has recently been described in animals. This utilizes the non-fermented sweetener sucralose, in addition to conventional sugars. It has been postulated that this test enables the simultaneous assessment of small-intestinal and colonic barrier function in humans. The aim of this study was to evaluate the triple sugar test using healthy volunteers and ileostomists. ⋯ Both sucralose and 51Cr-EDTA underwent significant colonic absorption. A significant amount of lactulose also appeared to be absorbed in the colon. This unexpected finding requires further study.