title: Monensin causes transient calcium ion influx into mouse splenic lymphocytes in a sodium ion-independent fashion.
abstract: Monensin, a Na(+) ionophore, can increase cytosolic free Ca(2+) concentration ([Ca(2+)](i)) in many cell types, but no studies have investigated the mechanism underlying a monensin-induced increase in [Ca(2+)](i) in immune cells. In view of this, we investigated the effect of monensin on [Ca(2+)](i) and cytosolic free Na(+) concentration ([Na(+)](i)) in mouse splenic lymphocytes using a fluorescence Ca(2+) indicator, fura-2, and a fluorescence Na(+) indicator, sodium-binding benzofuran isophthalate (SBFI), respectively. Monensin (1-100 microM) caused transient and sustained increases in [Ca(2+)](i) and [Na(+)](i), respectively, in a concentration-dependent manner. The monensin-induced increase in [Ca(2+)](i) was abolished by the omission of extracellular Ca(2+) or 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole hydrochloride (SKF-96365, 100-150 microM), and was largely inhibited by Ni(2+) (2-5 mM). The omission of extracellular Na(+) failed to inhibit the monensin-induced increases in [Ca(2+)](i). Furthermore, tetrodotoxin (1-10 microM), 5-(N,N-dimethyl)-amiloride (DMA, 10-20 microM), 2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline (SEA0400, 3-10 microM), verapamil (10-200 microM), nifedipine (10-200 microM), omega-agatoxin IVA (0.2-10 microM), omega-conotoxin GVIA (1-10 microM), omega-conotoxin MVIIC (0.5-10 microM), and nordihydroguaiaretic acid (NDGA, 1-10 microM) had no effect on the increases in [Ca(2+)](i). Monensin-induced Mn(2+) influx into splenic lymphocytes. The Mn(2+) influx was completely inhibited by SKF-96365. These results suggest that monensin transiently increases [Ca(2+)](i) in mouse splenic lymphocytes by stimulating Ca(2+) entry via non-selective cation channels in a Na(+)-independent manner.
authors.affiliation: Research Center for Animal Hygiene and Food Safety, Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, Japan. es@obihiro.ac.jp
authors.forename: Eiki
authors.initials: E
authors.lastname: Satoh
authors.forename: Kiyohiro
authors.initials: K
authors.lastname: Satoh
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D007473:Ion Channels; D007476:Ionophores / Q000008:administration & dosage / Q000494:pharmacology*; D008214:Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008345:Manganese / Q000378:metabolism; D051379:Mice; D008985:Monensin / Q000008:administration & dosage / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*; D013154:Spleen / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
chemical_list: D007473:Ion Channels; D007476:Ionophores; D008345:Manganese; D008985:Monensin; D012964:Sodium; D002118:Calcium