Microcalorimetric studies of tissue cells and bacteria

Abstract

AbstractAnalytical microcalorimetric studies of cultures of Enterobacter aerogenes and Clostridium pasteurianum revealed a complex pattern of heat production. While both organisms gave thermograms which followed the exponential growth curves in the early stages, the later events in the heat effect appeared to reflect deficiencies in the growth medium and induction of “secondary” nutrients. Synchronously dividing Schizosaccharomyces pombe is known to give maxima in oxygen uptake during the cell cycle. These peaks are enhanced by the uncoupling agent, 2‐oxomalononitrile m‐chlorophenylhydrazone (CCCP). The rate of heat production in control cultures pumped through the LKB microcalorimeter increased at a linear rate, doubling over each complete cell cycle. Introduction of CCCP to cultures gave an altered thermogram in which the maxima of heat evolution which occurred corresponded in time to the peaks in oxygen uptake.When suspensions of muscle fibroblasts from 9 day old chick embryos were pumped through the aeration vessel, they produced heat at a rate which was proportional to cell concentration. Inhibitors of respiration decreased heat evolution by similar percentages to their effect on oxygen uptake. Cells of the same type in monolayer gave slightly lower levels of heat production. The thermogram was characterised by maxima over 4 h, which may be a reflection of temporal changes in intracellular ATP levels. When muscle fibroblasts were mixed with excess (zero order kinetics) ATP and pumped through the gold vessel of the microcalorimeter, the rate of heat production was proportional to cell concentration, the latter representing the hydrolysing enzyme. 4,4′‐Dithiodi(nicotinic acid), a sulphydryl inhibitor which does not enter cells, depressed the calorimetric response vs cell concentration curve by 78%, indicating that a sulphydryl enzyme was present at the cell surface. Batch calorimetric experiments to determine the heat of interaction of antibodies with cells gave thermograms which differed in form and value, the latter changing in sign and magnitude. The results illustrate the need for careful model experiments to disect this complex system. The present results underline the value of microcalorimetry in giving analytical data on growth and respiration in cells and organisms and illustrates the potential of the technique in studies of surface‐localised reactions.