title: Role of sodium ion gradient in facilitating extracellular calcium influx.
abstract: The effect of extracellular Na+ on Ca++ influx in activated human platelets was evaluated with two methods. One method employed computer-aided subtraction of the time course of intracellular Ca++ changes in the absence of extracellular Ca++ from that observed in the presence of extracellular Ca++. The other utilized intracellular Ca++ elevation following the addition of Ca++ to a platelet suspension already activated by thrombin in the absence of extracellular Ca++. Both methods demonstrated that depletion of extracellular Na+ significantly attenuated Ca++ influx in activated platelets. That extracellular Na+ modifies the opening state of Ca++ channels was further substantiated with an experiment with Sr++ instead of Ca++. A flow cytometric study confirmed the validity of these experiments. Neither Na+/H+ exchange nor changes in the membrane potential appeared to be related to the effect of extracellular Na+ on Ca++ influx, and the mechanism by which extracellular Na+ permits Ca++ mobilization remains to be elucidated.
authors.affiliation: Department of Clinical, Yamanashi Medical College, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Ozaki
authors.forename: Y
authors.initials: Y
authors.lastname: Jinnai
authors.forename: Y
authors.initials: Y
authors.lastname: Yatomi
authors.forename: S
authors.initials: S
authors.lastname: Kume
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000814:Aniline Compounds; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors; D005434:Flow Cytometry; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000502:physiology*; D017923:Sodium-Hydrogen Exchangers; D013917:Thrombin / Q000378:metabolism; D014966:Xanthenes
chemical_list: D000814:Aniline Compounds; D002352:Carrier Proteins; D005456:Fluorescent Dyes; D017923:Sodium-Hydrogen Exchangers; D014966:Xanthenes; C059715:Fluo-3; C039465:5-dimethylamiloride; D000584:Amiloride; D012964:Sodium; D013917:Thrombin; D002118:Calcium; D016257:Fura-2