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1 Hypertension Research Center, 2 Molecular Resource Facility, and 4 Department of Pharmacology and Physiology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103; and 3 Department of Biochemistry and Molecular Biology, University of Calgary Health Science Center, Calgary, Alberta, Canada T2N 4N1
In this report, we have demonstrated that Na+/Ca2+ exchanger activity in a human megakaryocytic cell line (CHRF-288 cells) is K+ dependent, similar to the properties previously described for Na+/Ca2+ exchange activity in human platelets. With the use of RT-PCR techniques and mRNA, the exchanger expressed in CHRF-288 cells was found to be identical to that expressed in human retinal rods. Northern blot analysis of the mRNA for the human retinal rod exchanger in CHRF-288 cells revealed a major transcript at 5.8 kb with two minor bands at 4.9 and 6.8 kb. mRNA for the retinal rod exchanger was also identified in human platelets. Using Ba2+ influx as a measure of Na+/Ca2+ exchange activity in human platelets, we have demonstrated that exchange activity is driven by the transmembrane gradient for K+ as well as that for Na+. We propose that the K+ dependence of the platelet Na+/Ca2+ exchanger could make platelets especially sensitive to daily fluctuations in salt intake.
potassium; megakaryocytes; retinal rod; dense tubules; stroke
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