Effects of temperature on intracellular sodium, pH and cellular energy status in RIF-1 tumor cells

Most perfused tumor cell experiments are performed at 37degreesC, the normal healthy body temperature. However, the temperature of subcutaneously implanted tumors in small animals is generally 29-33degreesC when the rectal temperature of the animal is maintained at 37degreesC. We have investigated the acute effects of increasing the temperature of perfused radiation-induced-fibrosarcoma (RIF-1) tumor cells from 33 to 37degreesC (30 min) on intracellular sodium (Na-i(+)), intracellular pH (pH(i)), and bioenergetic status. Heating the cells by 4degreesC produced a reversible increase in Na-i(+), slight acidification and no change in nucleotide triphosphate to inorganic phosphate ratio (NTP/P-i) as measured by shift-reagent-aided Na-23 and P-31 NMR spectroscopy. In the presence of 3 muM 5-(N-ethyl-N-isopropyl) amiloride (EIPA), a potent and specific inhibitor of Na+/H+ antiporter, the increase in Na-i(+) during the heating was completely abolished suggesting that the heat induced increase in Na-i(+) was caused by an increase in Na+/H+ antiporter activity. However, the changes in pH(i) with the heating were identical with or without EIPA, indicating that pH(i) is controlled by other ion exchange mechanisms in addition to Na+/H+ antiporter. NTP/P-i was significantly higher in presence of EIPA for some time points during the heating suggesting that both NTP production and consumption rates may be altered during the heating. These results indicate that a slight increase in temperature from 33 to 37degreesC induces significant changes in Na+ physiology largely because of activation of Na+/H+ antiporter but other ion exchange mechanisms are also involved in maintaining pH(i) in the RIF-1 tumor cells. Thus, care must be taken in choosing the temperature for perfused cell studies. Copyright (C) 2004 John Wiley Sons, Ltd.