In:
American Journal of Physiology-Cell Physiology, American Physiological Society, Vol. 301, No. 6 ( 2011-12), p. C1325-C1343
Abstract:
Four patients with overhydrated cation leak stomatocytosis (OHSt) exhibited the heterozygous RhAG missense mutation F65S. OHSt erythrocytes were osmotically fragile, with elevated Na and decreased K contents and increased cation channel-like activity. Xenopus oocytes expressing wild-type RhAG and RhAG F65S exhibited increased ouabain and bumetanide-resistant uptake of Li + and 86 Rb + , with secondarily increased 86 Rb + influx sensitive to ouabain and to bumetanide. Increased RhAG-associated 14 C-methylammonium (MA) influx was severely reduced in RhAG F65S-expressing oocytes. RhAG-associated influxes of Li + , 86 Rb + , and 14 C-MA were pharmacologically distinct, and Li + uptakes associated with RhAG and RhAG F65S were differentially inhibited by NH 4 + and Gd 3+ . RhAG-expressing oocytes were acidified and depolarized by 5 mM bath NH 3 /NH 4 + , but alkalinized and depolarized by subsequent bath exposure to 5 mM methylammonium chloride (MA/MA + ). RhAG F65S-expressing oocytes exhibited near-wild-type responses to NH 4 Cl, but MA/MA + elicited attenuated alkalinization and strong hyperpolarization. Expression of RhAG or RhAG F65S increased steady-state cation currents unaltered by bath Li + substitution or bath addition of 5 mM NH 4 Cl or MA/MA + . These oocyte studies suggest that 1) RhAG expression increases oocyte transport of NH 3 /NH 4 + and MA/MA + ; 2) RhAG F65S exhibits gain-of-function phenotypes of increased cation conductance/permeability, and loss-of-function phenotypes of decreased and modified MA/MA + transport, and decreased NH 3 /NH 4 + -associated depolarization; and 3) RhAG transports NH 3 /NH 4 + and MA/MA + by distinct mechanisms, and/or the substrates elicit distinct cellular responses. Thus, RhAG F65S is a loss-of-function mutation for amine transport. The altered oocyte intracellular pH, membrane potential, and currents associated with RhAG or RhAG F65S expression may reflect distinct transport mechanisms.
Type of Medium:
Online Resource
ISSN:
0363-6143
,
1522-1563
DOI:
10.1152/ajpcell.00054.2011
Language:
English
Publisher:
American Physiological Society
Publication Date:
2011
detail.hit.zdb_id:
1477334-X
SSG:
12
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