Nitric oxide synthase isoenzymes during in vitro development of rat neuronal and human non-neuronal cells

We studied the expression of neuronal (n), endothelial (e) and inducible (i ) nitric oxide synthase (NOS) in cell cultures of rat mesencephalic neurons (embryonic day 14), human keratinocytes from juvenile epidermis, human end othelial cells from juvenile coronary arteries, and human osteoblasts. All cell types were cultured for 5, 10 or 15 days. During proliferation (round cells without processes), the intracellular distribution and the intracellu lar amount of the calcium-dependent NOS isoforms (n- and e-NOS) did not cha nge whereas the calcium-independent I-NOS changed from a cytosolic distribu tion pattern to compartmentalized distribution. A striking decrease of i-NO S immunoreactivity was measured by mea ns of image analysis. Our results su pport the opinion that I-NOS acts as a switch between proliferation and dif ferentiation of cells. (C) 2001 Elsevier Science ireland Ltd. All rights re served.