Kathleen Joan Sweadner, PhD
||Structure, function, and biological
roles of Na,K-ATPase isoforms in excitable
Structure, function, and biological roles of Na,K-ATPase
isoforms in excitable tissues.
The active transport of Na+ and K+ is carried out by
an ATP-hydrolyzing enzyme, the Na,K-ATPase. This laboratory
found that there are multiple isoforms of the enzyme
expressed in the nervous system and heart. Our research
concerns the control of isoform expression; the functional
properties of the different isoforms; and the molecular
structure of the protein itself.
Na,K-ATPase isoform expression is tissue- and cell
type-specific, but is regulated both developmentally
and in response to environmental factors. We have recently
found that the -2 isoform is expressed in glia only
when complex glial phenotypes are expressed in culture,
and in skeletal muscle myocytes only when they differentiate
to myotubes. Transfection of subunit isoforms in cells
in culture gives useful information about their functions,
particularly for glia, which show some unusual characteristics
suggesting a specialized role for the pump in K+ clearance.
Efforts to find straightforward kinetic differences
between isoforms have been controversial, and we now
think it likely that isoform-specific regulation by
second messengers is the key to understanding their
physiological significance. Protein kinase-mediated
regulation is being studied in purified enzyme preparations
and in cells in culture.
To investigate how the protein is folded and how its
conformational changes result in transport of ions,
we are mapping the epitopes of monoclonal antibodies,
using phage epitope library selection and DNA sequencing.
This, combined with protein chemistry, is a useful tool
for determining the enzyme's 3-dimensional structure.
Links: Representative Publications:
- Urayama, O, Shutt, H, Sweadner, KJ. Identification
of three isozyme proteins of the catalytic subunit
of the Na,K-ATPase in rat brain. J. Biol. Chem. 1989;
- Gloor, S, Antonicek, H, Sweadner, KJ, Pagliusi,
S, Frank, R, Moos, M, and Schachner, M. The adhesion
molecule on glia (AMOG) is a homologue of the beta
subunit of the Na,K-ATPase. J. Cell Biol. 1990; 110:
- McGrail, KM, Phillips, JM, and Sweadner, KJ. Immunofluorescent
localization of three Na,K-ATPase isozymes in the
rat central nervous system: Both neurons and glia
can express more than one Na,K-ATPase. J. Neurosci.
1991; 11: 381-391.
- Mohraz, M, Arystarkhova, E, and Sweadner, KJ. Immunoelectron
microscopy of epitopes on Na,K-ATPase catalytic subunit.
Implications for the transmembrane organization of
the C-terminal domain. J. Biol. Chem. 1994; 269: 2929-2936.
- Sweadner, KJ. Na,K-ATPase isoforms in glial cells.
in Neuroglial Cells, H. Kettenman and B. Ransom, Eds.,
Oxford University Press, 1994, in press.