English
 
User Manual Privacy Policy Disclaimer Contact us
  Advanced SearchBrowse

Item

ITEM ACTIONSEXPORT

Released

Journal Article

The sodium-calcium exchanger of bovine rod photoreceptors: K+-dependence of the purified and reconstituted protein

MPS-Authors
/persons/resource/persons252691

Friedel,  Ute
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

/persons/resource/persons253202

Wolbring,  Gregor
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

/persons/resource/persons253200

Wohlfahrt,  Paulus
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

/persons/resource/persons252599

Cook,  Neil J.
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

External Ressource
No external resources are shared
Fulltext (public)
There are no public fulltexts stored in PuRe
Supplementary Material (public)
There is no public supplementary material available
Citation

Friedel, U., Wolbring, G., Wohlfahrt, P., & Cook, N. J. (1991). The sodium-calcium exchanger of bovine rod photoreceptors: K+-dependence of the purified and reconstituted protein. Biochimica et Biophysica Acta-Biomembranes, 1061(2), 247-252. doi:10.1016/0005-2736(91)90290-O.


Cite as: http://hdl.handle.net/21.11116/0000-0007-8361-7
Abstract
The K+-dependence of the rod photoreceptor sodium-calcium exchanger was investigated using the Ca2+-sensitive dye arsenazo III after reconstitution of the purified protein into proteoliposomes. The uptake of Ca2+ by Na+-loaded liposomes was found to be greatly enhanced by the presence of external K+ (EC50 ≃ 1 mM) in a Michaelis-Menten manner, suggesting that one K+ ion is involved in the transport of one Ca2+ ion. We also found a minimal degree of Ca2+ uptake in the total absence of K+. Other alkali cations, notably Rb+ and, to a lesser extent, Cs+, were also able to stimulate Na+single bondCa2+ exchange. We also investigated the K+-dependence of the photoreceptor Na+single bondCa2+ exchanger by determining the effects of electrochemical K+ gradients on the Na+-activated Ca2+ efflux from proteoliposomes. We found that, under conditions of membrane voltage clamp with FCCP, inwardly directed electrochemical K+ gradients (i.e., K0+ > Ki+) inhibited, whereas an outwardly directed electrochemical K+ gradient (i.e., Ki+ > K0+) enhanced, Na+-dependent Ca2+ efflux, consistent with the notion that K+ is cotransported in the same direction as Ca2+. The investigation of the reconstituted exchanger at physiological (i.e. Ki+=110mM, K0+= 2.5mM) potassium concentrations revealed that the Na+-dependence of Ca2+-efflux was highly cooperative (n = 3.01 from Hill plots), indicating that at least three, but possibly four, Na+ ions are exchanged for one Ca2+ ion. Under these conditions the reconstituted exchanger showed a Km for Na+ of 26.1 mM, and a turnover number of 115 Ca2+·s−1 per exchanger molecule. Our results with the purified and reconstituted sodium-calcium exchanger from rod photoreceptors are therefore consistent with previous reports (Cervetto, L., Lagnado, L., Perry, R.J., Robinson, D.W. and McNaughton, P.A. (1989) Nature 337, 740–743; Schnetkamp, P.P.M., Basu, D.K. and Szerencsei, R.T. (1989) Am. J. Physiol. 257, C153–C157) that the sodium-calcium exchanger of rod photoreceptors otransports K+ under physiological conditions with a stoichiometry of 4 Na+; 1 Ca2+, 1 K+.