Na+/K+ ATPase activity in mouse lung fibroblasts and HeLa S3 cells during and after hyperthermia

Controlled radio-frequency hyperthermia using an MR scanner and simultaneous monitoring of temperature and therapy response by (1)H, (23)Na and (31)P magnetic resonance spectroscopy in subcutaneously implanted 9L-gliosarcoma

A magnetic resonance (MR) technique is developed to produce controlled radio-frequency (RF) hyperthermia (HT) in subcutaneously-implanted 9L-gliosarcoma in Fisher rats using an MR scanner and its components; the scanner is also simultaneously used to monitor the tumour temperature and the metabolic response of the tumour to the therapy. The method uses the (1)H chemical shift of thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra-acetic acid (TmDOTA(-)) to monitor temperature. The desired HT temperature is achieved and maintained using a feedback loop mechanism that uses a proportional-integral-derivative controller. The RF HT technique was able to heat the tumour from 33 degrees to 45 degrees C in approximately 10 min and was able to maintain the tumour temperature within +/-0.2 degrees C of the target temperature (45 degrees C). Simultaneous monitoring of the metabolic changes with RF HT showed increases in total tissue and intracellular Na(+) as measured by single-quantum and triple-quantum filtered (23)Na MR spectroscopy (MRS), respectively, and decreases in intra- and extracellular pH and cellular bioenergetics as measured by (31)P MRS. Monitoring of metabolic response in addition to the tumour temperature measurements may serve as a more reliable and early indicator of therapy response. In addition, such measurements during HT treatment will enhance our understanding of the tumour response mechanisms during HT, which may prove valuable in designing methods to improve therapeutic efficiency.

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

Most perfused tumor cell experiments are performed at 37 degrees C, the normal healthy body temperature. However, the temperature of subcutaneously implanted tumors in small animals is generally 29-33 degrees C when the rectal temperature of the animal is maintained at 37 degrees C. We have investigated the acute effects of increasing the temperature of perfused radiation-induced-fibrosarcoma (RIF-1) tumor cells from 33 to 37 degrees C (30 min) on intracellular sodium (Na(i)+) , intracellular pH (pH(i)), and bioenergetic status. Heating the cells by 4 degrees C 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 (23)Na and (31)P NMR spectroscopy. In the presence of 3 microM 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 37 degrees C 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.

Role of cellular membranes in hyperthermia: some observations and theories reviewed

We have re-examined critically the evidence for and against the involvement of membranes in determining the response of cells to acute and chronic heat stress. Although frequently dismissed by many in the past, we believe that the bulk of evidence presented supports the view that physical and compositional alterations of membrane lipid components, both during and subsequent to heat exposure may, at least in part, account for cell adaptation, malfunction and lethality. Our primary goal in this review is to generate renewed interest in testing the validity of this hypothesis.