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The Retinal Rod Na-Ca+K Exchanger
Conan B. Cooper,
Joseph E. Tucker,
Robert T. Szerencsei,
Robert J. Winkfein, and
Paul P.M. Schnetkamp*
Department of Physiology & Biophysics and
Keywords: calcium, Na-Ca exchange, vision, photoreceptors The retinal rod Na-Ca+K exchanger (NCKX) utilizes the inward sodium gradient and the outward potassium gradient across the rod outer segment plasma membrane to extrude calcium that enters in darkness via the cGMP-gated channels. Previously, we have described functional properties of the native Na-Ca+K exchanger including those of the cation binding sites and regulation of the maximal rate of transport. The first NCKX cDNA was cloned from a bovine retinal cDNA library (Reiländer et al. EMBO J. 11, 1689). Here, we have examined heterologous expression of protein and function of bovine NCKX, as well as of human NCKX (Tucker et al., IOVS, 39, 435) and dolphin NCKX cDNA recently cloned by us. No consistent function was observed with either bovine or human cDNA although large amounts of protein could be observed under certain conditions. In contrast, robust potassium-dependent Na-Ca exchange activity was observed with the dolphin rod NCKX cDNA. Functional activity was observed as potassium-dependent calcium influx upon reversal of the transmembrane sodium gradient as imaged with Fura-2 or measured by 45Ca uptake. These observations will be discussed in the context of the sequence differences observed for the three different NCKX cDNAs. Supported by the MRC of Canada. | Discussion Board | Next Page | Your Symposium | Cooper, C.B.; Tucker, J.E.; Szerencsei, R.T.; Winkfein, R.J.; Schnetkamp, P.P.M.(1998). The Retinal Rod Na-Ca+K Exchanger. Presented at
INABIS '98 - 5th Internet World Congress on Biomedical Sciences at McMaster University, Canada, Dec 7-16th. Invited Symposium. Available
at URL /www.mcmaster.ca/inabis98/ |