title: Heat-induced changes in intracellular Na+, pH and bioenergetic status in superfused RIF-1 tumour cells determined by 23Na and 31P magnetic resonance spectroscopy.
abstract: The acute effects of hyperthermia on intracellular Na+ (Nai+), bioenergetic status and intracellular pH (pHi) were investigated in superfused Radiation Induced Fibrosarcoma-1 (RIF-1) tumour cells using shift-reagent-aided 23Na and 31P nuclear magnetic resonance (NMR) spectroscopy. Hyperthermia at 45 degrees C for 30 min produced a 50% increase in Na, a 0.42 unit decrease in pHi and a 40-45% decrease in NTP/P(i). During post-hyperthermia superfusion at 37 degrees C, pHi and NTP/P(i) recovered to the baseline value, but Na initially decreased and then increased to the hyperthermic level 60 min after heating. Hyperthermia at 42 degrees C caused only a 15-20% increase in Nai+. In the presence of 3 microM 5-(N-ethyl-N-isopropyl)amiloride (EIPA), an inhibitor of the Na+/H+ exchanger, the increase in Nai+ during 45 degrees C hyperthermia was attenuated, suggesting that the heat-induced increase in Nai+ was mainly due to an increase in Na+/H+ anti-porter activity. EIPA did not prevent hyperthermia-induced acidification. This suggests that pHi is controlled by other ion exchange mechanisms in addition to the Na+/H+ exchanger. EIPA increased the thermo-sensitivity of the RIF-1 tumour cells only slightly as measured by cell viability and clonogenic assays. The hyperthermia-induced irreversible increase in Nai+ suggests that changes in transmembrane ion gradients play an important role in cell damage induced by hyperthermia.
authors.affiliation: Department of Radiology, Indiana University School of Medicine, 950 West Walnut Street, R2 E124, Indianapolis, Indiana 46202, USA. ababsky@iupui.edu
authors.forename: A
authors.initials: A
authors.lastname: Babsky
authors.forename: S K
authors.initials: SK
authors.lastname: Hekmatyar
authors.forename: T
authors.initials: T
authors.lastname: Gorski
authors.forename: D S
authors.initials: DS
authors.lastname: Nelson
authors.forename: N
authors.initials: N
authors.lastname: Bansal
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology*; D045744:Cell Line, Tumor; D005354:Fibrosarcoma / Q000378:metabolism* / Q000628:therapy; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D006979:Hyperthermia, Induced / Q000009:adverse effects*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D010759:Phosphorus Isotopes; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects*
chemical_list: D010759:Phosphorus Isotopes; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium; C039614:ethylisopropylamiloride