title: Sodium calcium exchanger operates in the reverse mode in metastatic human melanoma cells.
abstract: Cytosolic Ca2+ ([Ca2+]cyt) is important in the regulation of several cellular functions involved in metastasis. We hypothesize that distinct [Ca2+]cyt regulation explains the acquisition of a more metastatic phenotype. To test this hypothesis, we used highly and lowly metastatic human melanoma cells and [Ca2+]cyt was monitored using Fura&mdash;2AM and fluorescence spectroscopy. Stimulation with ATP elicited a sustained increase in [Ca2+]cyt in highly metastatic cells, but a transient increase in lowly metastatic cells. Na+ substitution revealed Na+/Ca2+ exchanger (NCX) activity in reverse mode in highly, but not in lowly metastatic cells. In highly metastatic cells, addition of Na+ in the plateau phase of [Ca2+]cyt increase elicited with ATP, in the absence of Na+, resulted in a rapid return to basal, indicating that NCX can operate in both reverse and forward modes. Inhibition and knockdown of NCX, using KB&mdash;R7943 and siRNA NCX&mdash;1 respectively, supported the significance of NCX in [Ca2+]cyt regulation in highly metastatic cells. Stimulation with UTP triggered a rapid increase in highly metastatic cells [Ca2+]cyt, but not in lowly metastatic cells suggesting that highly and lowly metastatic cells exhibit distinct purinergic receptors. These data indicate that following agonist&mdash;stimulation, NCX operates preferentially in the reverse mode to enable a sustained [Ca2+]cyt increase in highly metastatic cells. The forward mode of NCX operation to extrude Ca2+ is preferred in lowly metastatic cells. The acquisition of a more metastatic phenotype involves a switch in NCX activity from forward to reverse mode that is favorable to maintain elevated [Ca2+]cyt in response to agonist stimulation.
authors.affiliation: Texas Tech University Health Sciences Center Departments of Cell Physiology & Molecular Biophysics Lubbock USA.
authors.forename: S R
authors.initials: SR
authors.lastname: Sennoune
authors.affiliation: Texas Tech University Health Sciences Center Departments of Cell Physiology & Molecular Biophysics Lubbock USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Santos
authors.affiliation: Texas Tech University Departments of Mechanical Engineering Lubbock USA.
authors.forename: F
authors.initials: F
authors.lastname: Hussain
authors.affiliation: Texas Tech University Health Sciences Center Departments of Cell Physiology & Molecular Biophysics Lubbock USA Raul.Martinez-Zaguilan@ttuhsc.edu.
authors.forename: R
authors.initials: R
authors.lastname: Martínez-Zaguilán
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D055785:Gene Knockdown Techniques; D006801:Humans; D008545:Melanoma / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology*; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014544:Uridine Triphosphate / Q000494:pharmacology
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D004791:Enzyme Inhibitors; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D010042:Ouabain; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D013890:Thiourea; D002118:Calcium; D014544:Uridine Triphosphate