Maitotoxin-induced free Ca changes in single rat hepatocytes

We report the results using bioluminescent and fluorescent indicators to in vestigate maitotoxininduced free Ca changes in single rat hepatocytes. Mait otoxin generated a steadily rising free Ca increase after a long lag period . The free Ca increase was dependent on extracellular calcium and could be antagonised by chelation of extracellular calcium or the inclusion of nicke l in the superfusate. Manganese-induced quench of cytoplasmic Fura2 dextran revealed an accelerated rate of calcium entry during the final period of t he lag phase, immediately prior to the free Ca increase. Imaging experiment s demonstrated a markedly different part of free Ca mobilisation compared w ith glycogenolytic stimuli. Moreover, the use of a combination of hormonal stimuli and maitotoxin revealed that some cells could exhibit free Ca oscil lations despite steadily rising intracellular free Ca level. The significan ce of these observations in terms of the mechanism of action of maitotoxin and the mechanism of free Ca transient generation is discussed. (C) 1999 Pu blished by Elsevier Science Inc.