English
 
Help Privacy Policy Disclaimer
  Advanced SearchBrowse

Item

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

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.

Item is

Basic

show hide
Genre: Journal Article

Files

show Files

Locators

show

Creators

show
hide
 Creators:
Friedel, Ute1, Author           
Wolbring, Gregor1, Author           
Wohlfahrt, Paulus1, Author           
Cook, Neil J.1, Author           
Affiliations:
1Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society, ou_2068290              

Content

show
hide
Free keywords: Sodium-calcium ion exchange; Photoreceptor; Potassium dependence; ROSrod outer segment; cGMP; guanosine 3′,5′-cyclic monophosphate; DTT, dithiothreitol; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate; Hepes, N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid
 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+.

Details

show
hide
Language(s): eng - English
 Dates: 1990-06-252003-04-041991-01-30
 Publication Status: Published in print
 Pages: 6
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1016/0005-2736(91)90290-O
 Degree: -

Event

show

Legal Case

show

Project information

show

Source 1

show
hide
Title: Biochimica et Biophysica Acta-Biomembranes
Source Genre: Journal
 Creator(s):
Affiliations:
Publ. Info: Amsterdam : Elsevier
Pages: - Volume / Issue: 1061 (2) Sequence Number: - Start / End Page: 247 - 252 Identifier: ISSN: 0005-2736
CoNE: https://pure.mpg.de/cone/journals/resource/954926938702