Biomedical subjects

L V Virkki

Publications and source records attributed to L V Virkki.

4 recordsLinked to original sources

PubMed1998

Two distinct K+ channels in lamprey (Lampetra fluviatilis) erythrocyte membrane characterized by single channel patch clamp.

Two channels, distinguished by using single-channel patch-clamp, carry out potassium transport across the red cell membrane of lamprey erythrocytes. A small-conductance, inwardly rectifying K(+)-selective channel was observed in both isotonic and hypotonic solutions (osmolarity decreased by 50%). The single-channel conductance was 26 +/- 3 pS in isotonic (132 mM K+) solutions and 24 +/- 2 pS in hypotonic (63 mM K+) solutions. No outward conductance was found for this channel, and the channel activity was completely inhibited by barium. Cell swelling activated another inwardly rectifying K+ channel with a larger inward conductance of 65 pS and outward conductance of 15 pS in the on-cell configuration. In this channel, rectification was due to the block of outward currents by Mg2+ and Ca2+ ions, since when both ions were removed from the cytosolic side in inside-out patches the conductance of the channel was nearly ohmic. In contrast to the small-conductance channel, the swelling-activated channel was observed also in the presence of barium in the pipette. Neither type of channel was dependent on the presence of Ca2+ ions on the cytosolic side for activity.

Animals↗

PubMed1998

Regulation of ion transport across lamprey (Lampetra fluviatilis) erythrocyte membrane by oxygen tension.

We have measured the effects of oxygen tension on the transport of Na+, K+ and Cl- across the erythrocyte membrane of the lamprey Lampetra fluviatilis. The transport of each ion was affected by the oxygen tension of the medium. Hypoxic conditions (PO2 2 kPa) caused an increase in the acidification-induced influx of Na+ via Na+/H+ exchange. The influx of K+ was only slightly affected by the oxygenation of the medium. In contrast, the basal K+ efflux, measured using the radioactive isotope 43K, was markedly reduced by decreasing the oxygen tension of the medium, whereas the K+ flux in hypotonic medium was not affected. Only minor effects of hypoxic conditions on the influx of Cl- were observed in either isotonic or hypotonic conditions (there was a tendency for the isotonic influx to increase) or on the efflux in isotonic conditions. However, deoxygenation caused a marked reduction in the Cl- efflux in hypotonic conditions. The results show that oxygen tension has a marked effect on the pH and volume regulatory transport pathways of lamprey erythrocytes. For K+ and Cl-, the regulation appears to be asymmetric, i.e. influx and efflux are affected differently.

Animals↗

PubMed1995

Regulatory volume decrease in lamprey erythrocytes: mechanisms of K+ and Cl- loss.

The nature of the swelling-activated K+ and Cl- transport pathways of lamprey (Lampetra fluviatilis) erythrocytes was studied. In isosmotic medium, unidirectional K+ and Cl- effluxes appear to be largely mediated by conductive pathways. Unidirectional Cl- efflux increased as a function of a decrease in medium osmolarity. The swelling-activated Cl- transport was inhibited by R(+)-[(2-n-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inde n-5- yl)oxy]acetic acid (DIOA), furosemide, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). In contrast, moderate cell swelling did not increase unidirectional ouabain-insensitive K+ efflux. However, inhibition of transport by Ba2+ was markedly reduced. This suggests that the Ba(2+)-sensitive pathway that mediated most of the K+ efflux in isosmotic conditions was inhibited by cell swelling and a Ba(2+)-insensitive pathway was activated. DIOA had no effect on K+ efflux in isosmotic or hyposmotic medium. These data and the finding that substitution of NO3- or SCN- for Cl- had only a minor effect on the swelling-induced net extrusion of K+ and water indicate that the pathways for K+ and Cl-, activated by cell swelling, are conductive.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1995

Haemoglobin function in intact lamprey erythrocytes: interactions with membrane function in the regulation of gas transport and acid-base balance.

Haemoglobin function within lamprey erythrocytes offers a unique solution to gas transport among vertebrates. Lamprey haemoglobin within intact erythrocytes is in oligomer/monomer equilibrium and has an oxygen affinity similar to that of haemoglobin in other active fishes. The cooperativity of oxygen binding, which is reduced at low pH values, the effect of protons and the effect of the concentration of haemoglobin on its oxygen affinity are all due to dissociation/association reactions of the haemoglobin molecules. The permeability of the lamprey red cell membrane to acid and base equivalents is very low, and plasma bicarbonate cannot therefore be dehydrated to carbon dioxide to any significant extent during the residence time of blood in the gills. This potential limitation on carbon dioxide excretion is overcome, however, by the high intraerythrocytic pH and the marked oxygenation-linked pH changes in the erythrocyte, which are due to the large Haldane effect of the haemoglobin. Owing to the relative impermeability of the erythrocyte membrane to acid equivalents, intraerythrocytic haemoglobin cannot take part in the acid-base buffering of the extracellular compartment. As a consequence, extracellular acid loads cause marked fluctuations in plasma pH.

Animals↗