There are conflicting results concerning the receptor subtype(s) involved in calcium-mediated endothelin signaling in the glial cells. In order to elucidate the role of endothelin A and B receptors in these processes, we have studied the effect of a complex spectrum of endothelin receptor ligands on intracellular calcium concentration changes in proliferating and differentiated C6 rat glioma cells. Cell differentiation was induced by dibutyryl-cAMP and assessed by the glial fibrillar acidic protein content. Intracellular calcium changes were measured in cell suspensions using fluorescent probe Fura-2. The specific endothelin B receptor agonists sarafotoxin S6c and IRL-1620 did not influence the intracellular calcium concentration. However, calcium changes induced by endothelin-1 and especially by endothelin-3 after the pretreatment of cells with one of these endothelin B receptor specific agonists were significantly enhanced even above the values attained by the highest effective endothelin concentrations alone. Such endothelin B-receptor ligand-induced sensitization of calcium signaling was not observed in differentiated C6 cells. Moreover, endothelin-induced calcium oscillations in differentiated C6 cells were less inhibited by BQ-123 and BQ-788 than in their proliferating counterparts. In conclusion, the specific activation of endothelin B receptor in C6 rat glioma cells does not affect intracellular calcium per se, but probably does so through interaction with the endothelin A receptor. The pattern and/or functional parameters of endothelin receptors in C6 rat glioma cells are modified by cell differentiation., R. Malík, K. Vlašicová, A. Šedo., and Obsahuje bibliografii
Quaternary benzo[c]phenanthridine alkaloids (QBA), fagaronine (FA), sanguinarine (SA), chelerythrine (CHE) and the QBA extract from Macleya cordata (EX) exerted differential inhibitory effect on the hydrolytic activity of particular dipeptidyl peptidase (DPP)-like enzyme isolated from human blood plasma and from human and rat glioma cell lines. The low-MW form of DPP-IV-like enzyme activity, corresponding most probably to DPP-8, observed only in glioma cells but not in human plasma, was inhibited preferentially by SA, CHE and EX, and only slightly by FA. The alkaloid inhibitory effect was concentration-dependent in the range 25-150 M and directly pH-related. In addition, a subtle but consistent inhibition of the intermediate-MW form of DPP-IV-like enzyme activity, ascribed to DPP-IV/CD26, observed only in human plasma and of the attractin (high-MW form of DPP-IV-like enzyme activity, expressed in U87 glioma cells) by the studied alkaloids was observed. We conclude that some of the QBA biological effects could be determined by tissue and cell type specific dipeptidyl peptidase IV-like molecules expression pattern., A. Šedo, R. Malík, J. Vičar, V. Šimánek, J. Ulrichová., and Obsahuje bibliografii