Kinetics of the toxic action of Pb2+ on Rhizopus nigricans as studied by microcalorimetry

The microcalorimetric bioassay for acute cellular toxicity is based on meta bolic heat production from cultured cells. Microcalorimetry is a quantitati ve, inexpensive, and versatile method for measuring acute toxicity. The bio logical response to toxicants is the inhibition of the heat production rate in cells and toxicity is expressed as the concentration of toxicant that i s 50% effective in this inhibition (IC50) In this paper, the effect of Pb2 on Rhizopus nigricans growth was investigated at 25 degrees C. The relatio nship between growth rate constants (k) and concentration of Pb2+ (C) is k = 0.04226 exp[-3.636 x 10(-5) (C + 177.0)(2)], and IC50 is 47.5 mu g ml(-1) . These signals are readily obtained by an LKB 2277-204 heat conduction mic rocalorimeter. This system can therefore measure acute toxicity for a broad range of toxicants having target sites in various cellular metabolic pathw ays. (C) 1999 Elsevier Science B.V. All rights reserved.