AbstractChlorotetracycline calcium fluorescence studies have been carried out on acute and chronic capsaicin treated rat lung mitochondria and microsome membrane fractions in the presence of different concentrations of capsaicin (1–100 nM) underin vivoconditions. Results indicate, that acute capsaicin treated rat lung membrane fractions are quite different from those that are chronically treated, with respect to capsaicin mediated calcium permeability, measured in terms of calcium induced CTC fluorescence alterations. It seems that the reported ‘activation’ phenomena of acute capsaicin treatment may be associated with calcium influx across the membrane. On the other hand, the reported ‘desensitization’ phenomena of chronic capsaicin treatment may be due to inhibition of capsaicin mediated calci