Role of K+ and amino acids in osmoregulation by the free-living microaerophilic protozoon Hexamita inflata.
The primitive free-living protozoon Hexamita inflata was found to maintain a cell volume of approximately 260 fI under standard culture conditions. On increasing the extracellular osmolality the volume decreased and the cells remained shrunken for >30 min. By contrast, a decrease in the external osmolality resulted in a transient increase in cell volume which was followed by an efficient 'regulatory volume decrease' (RVD). H. inflata contains high concentrations of amino acids, with alanine constituting over 70% of the total amino acid pool. Exposure to hypo-osmotic medium resulted in the loss from the cell of both amino acids and K+, via one or more swelling-activated pathways. The efflux of amino acids and K+, together with a charge-balancing counter-anion, accounted almost fully for the observed RVD. The pharmacological properties of the swelling-activated pathways differ from those of volume-sensitive transporters and channels described previously in other cell types.
Biagini
Giancarlo A
GA
School of Biochemistry and Molecular Biology, University of New South Wales, Sydney, NSW 2052, Australia1.
Kirk
Kiaran
K
Division of Biochemistry and Molecular Biology, Australian National University, Canberra, ACT 0200, Australia2.
Schofield
Phillip J
PJ
School of Biochemistry and Molecular Biology, University of New South Wales, Sydney, NSW 2052, Australia1.
Edwards
Michael R
MR
School of Biochemistry and Molecular Biology, University of New South Wales, Sydney, NSW 2052, Australia1.
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D003470:Culture Media; D056890:Eukaryota / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D014882:Water-Electrolyte Balance
D000596:Amino Acids; D003470:Culture Media; D012413:Rubidium; D011188:Potassium