The ContiNet of the International Continence Society

We have examined the reversal of the regulatory effect of growth factors on calpain/calpastatin activity in transfected Schwann cells (tSc) after their subsequent withdrawal. Removal of nerve growth factor (NGF) or cyclic adenosine monophosphate (cAMP) from tSc resulted in a smaller loss of mu calpain (37%) and mcalpain (36.5 %) activity compared to treated cells from which the growth factors were not withdrawn. The mu calpain activity increased approximately 12% following withdrawal of acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF) at 24 hr, while the increased mcalpain activity was more than 30-40% compared with that of cells that were continuously treated. The activity of both isoforms returned to their normal levels (untreated) at 48-72 hr following withdrawal of various growth factors, including NGF, cAMP, aFGF, bFGF, platelet-derived growth factor aa (PDGFaa), and PDGFbb. The inhibitory activity of calpastatin was greater than control following withdrawal of NGF, cAMP, PDGFaa, or PDGFbb at 24 hr and this inhibitory activity was less with treatment by aFGF and bFGF. The control activity was restored at 48 hr following withdrawal of these factors. The intensity of the cytoplasmic calpain immunoreactivity was significantly decreased in the nuclear and non-nuclear regions of the cytoplasm, respectively, following withdrawal of cAMP at 144 hr. Removal of bFGF from the medium resulted in an increase of cytoplasmic calpain immunoreactivity in the nuclear regions and cytoplasm, while there was dramatic loss of myelin calpain immunoreactivity from both the nuclear region and cytoplasm. The changes in calpain activity and immunoreactivity in tSc following withdrawal of growth factors suggest that release of calpain from membrane to cytosol may be regulated by these factors.