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Huppertz, B; Bauer, PJ.
Na(+)-Ca2+,K+ exchange in bovine retinal rod outer segments: quantitative characterization of normal and reversed mode.
Biochim Biophys Acta. 1994; 1189(2):119-126 Doi: 10.1016/0005-2736(94)90056-6
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Leading authors Med Uni Graz: Huppertz Berthold
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Abstract:: Ca2+ homeostasis of bovine retinal rod outer segments is maintained through Na(+)-Ca2+,K+ exchangers and cGMP-gated channels in the plasma membrane. It has recently been demonstrated that both proteins are associated. This novel finding allowed us to investigate quantitatively normal and reversed mode Na(+)-Ca2+,K+ exchange in rod outer segment membrane vesicles and reconstituted proteoliposomes both containing exchangers in rightside-out and inside-out orientations. Addition of Na+ activated both normal and reversed mode exchange; if, however, initially Ca2+ from vesicles containing inside-out oriented exchangers has been released by activation of the associated channels, only normal mode exchange was observed upon addition of Na+. Using this approach, the fractions of vesicles containing rightside-out and inside-out oriented exchangers were about similar in these vesicle preparations. Normal and reversed mode exchange had similar Na+ concentrations of about 70 mM for half maximal activation (in the presence of 115 mM K+) and cooperativity parameters, nHill, of about 2.0. Furthermore, both modes were electrogenic, and showed only little Na(+)-Ca2+,K+ exchange in the absence of K+. The two modes of exchange differed, however, in the maximal exchange rate, the normal mode being about twice as fast as the reversed mode.
Find related publications in this database (using NLM MeSH Indexing): Animals -; Carrier Proteins - chemistry; Cattle -; Electrochemistry -; Proteolipids -; Rod Cell Outer Segment - metabolism; Sodium-Calcium Exchanger -
Find related publications in this database (Keywords): SODIUM-CALCIUM ION EXCHANGE; PHOTORECEPTOR; ROD OUTER SEGMENT; PROTEIN ASSOCIATION; VESICLE SIDEDNESS; (BOVINE)