The effect of Na+ on Ca2+ homeostasis in unstimulated platelets.
نویسنده
چکیده
Platelets maintain a low cytosolic free Ca2+ concentration by limiting Ca2+ influx from plasma and promoting Ca2+ efflux. The present studies examine the role of the plasma membrane Na+ gradient in these processes. The Na+ gradient in intact unstimulated platelets was altered by incubating the platelets with ouabain or by replacing extracellular Na+ with N-methyl-D-glucamine or choline. Ca2+ flux across the plasma membrane and the amount of exchangeable Ca2+ in the platelet cytosol were measured by observing 45Ca2+ influx and efflux under steady-state conditions. The cytosolic free Ca2+ concentration was measured with the fluorescent probe quin2. At extracellular Na+ concentrations below 50 mM, the size of the cytosolic exchangeable Ca2+ pool increased by 48%. The size of the exchangeable Ca2+ pool sequestered in the dense tubular system increased by 356%. Ca2+ flux across the plasma membrane increased by 38%. There was, however, no change in total platelet Ca2+ and little, if any, change in the cytosolic free Ca2+ concentration. Similar effects were produced by incubating platelets with ouabain. These observations demonstrate a marked influence of the plasma membrane Na+ gradient on Ca2+ homeostasis in platelets. The nature of the changes, however, suggests that Na+/Ca2+ exchange cannot be sole basis for Ca2+ efflux from platelets.
منابع مشابه
Ca2+ homeostasis in unstimulated platelets.
Unstimulated platelets maintain a low cytosolic free Ca2+ concentration and a steep plasma membrane Ca2+ gradient. The mechanisms that are required have not been completely defined. In the present studies, 45Ca2+ was used to examine the kinetics of Ca2+ exchange in intact unstimulated platelets. Quin2 was used to measure the cytosolic free Ca2+ concentration. Under steady-state conditions, the ...
متن کاملOuabain increases the calcium concentration in intracellular stores involved in stimulus-response coupling in human platelets.
The effect of ouabain on Ca2+ homeostasis in human platelets was studied using both quin 2 and chlorotetracycline to monitor changes in cytosolic Ca2+ as well as changes in the amount of Ca2+ accumulated in intracellular storage sites. In resting platelets, ouabain induces a concentration- and time-dependent increase in cytosolic Ca2+ concentration and a marked elevation of Ca2+ in the intracel...
متن کاملIdentification and function of the high affinity binding sites for Ca2+ on the surface of platelets.
Extracellular Ca2+ is required for platelet aggregation and secretion in response to ADP or epinephrine. Recently, we reported that the platelet surface contains two classes of high affinity binding sites for extracellular Ca2+. To identify these sites and clarify their role in platelet function, we have now (a) studied platelets congenitally deficient in surface membrane glycoproteins and (b) ...
متن کاملInduction of apoptosis in human tumor cell lines by platelets
Introduction: It has been reported that platelets can eradicate tumor cells in vitro, although the mechanism of this effect has not been determined. The effect of platelets on the induction of apoptosis in tumor cells is largely unknown. Materials and methods: To investigate this effect, two human hematologic cell lines, K562 and Daudi, were independently faced with unstimulated and thromb...
متن کاملEffect of glycine betaine and salinity on photosynthetic pigments and ion concentration of safflower
The influence of exogenous application of glycine betaine (GlyBet) was examined on photosynthetic pigments and ions concentration of safflower under salinity stress conditions. The experiment was performed in a randomized complete block design arranged as a factorial with three replications. Salinity treatments (0, 50, 100, and 150 mM) were applied using sodium chloride (NaCl). GlyBet (0, 10, 3...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- The Journal of biological chemistry
دوره 259 20 شماره
صفحات -
تاریخ انتشار 1984