Vol. 283, Issue 2, C512-C520, August 2002
Determinants of cardiac Na+/Ca2+
exchanger temperature dependence: NH2-terminal
transmembrane segments
Christian
Marshall1,*,
Chadwick
Elias2,*,
Xiao-Hua
Xue1,*,
Hoa Dinh
Le2,
Alexander
Omelchenko2,
Larry V.
Hryshko2, and
Glen F.
Tibbits1,3
1 Cardiac Membrane Research Laboratory, Simon Fraser
University, Burnaby, British Columbia V5A 1S6;
2 Institute of Cardiovascular Sciences, St. Boniface
General Hospital Research Centre, University of Manitoba, Winnipeg,
Manitoba R2H 2A6; and 3 Cardiovascular Sciences,
British Columbia Research Institute for Children and Women's
Health, Vancouver, British Columbia, Canada V5Z 4H4
The cardiac
Na+/Ca2+ exchanger (NCX) in trout
exhibits profoundly lower temperature sensitivity in comparison to the
mammalian NCX. In this study, we attempt to characterize the regions of the NCX molecule that are responsible for its temperature sensitivity. Chimeric NCX molecules were constructed using wild-type trout and
canine NCX cDNA and expressed in Xenopus oocytes.
NCX-mediated currents were measured at 7, 14, and 30°C using the
giant excised-patch technique. By using this approach, the differential
temperature dependence of NCX was found to reside within the
NH2-terminal region of the molecule. Specifically, we found
that ~75% of the Na+/Ca2+ exchange
differential energy of activation is attributable to sequence
differences in the region that include the first four transmembrane
segments, and the remainder is attributable to transmembrane segment
five and the exchanger inhibitory peptide site.
myocardial contractility; excitation-contraction coupling; salmonid; calcium handling
*
C. Marshall, C. Elias, and X.-H. Xue contributed equally
to this work.
