NIMODIPINE AND NITRENDIPINE INHIBIT N-TYPE CALCIUM CHANNELS IN DIBUTYRYL CAMP-DIFFERENTIATED NEUROBLASTOMA X GLIOMA HYBRID (NG-108-15) CELLS

The effects of nifedipine, niguldipine, nimodipine and nitrendipine on the high K+-induced intracellular Ca2+ ([Ca2+](i)) transient in dibut yryl cAMP-differentiated neuroblastoma x glioma hybrid NG 108-15 cells were studied by using the fluorescent Ca2+ indicator fura-2. It was o bserved that nifedipine at the concentration of 50 mu M inhibited the high K+-induced [Ca2+](i) transient by about 60%; niguldipine at the c oncentration of 10 mu M caused a reduction of about 65% in the high K-induced calcium signal and a further increase in the concentration up to 50 mu M did not result in a significant further reduction in the h igh K+-induced calcium signal. However, on the other hand, nimodipine and nitrendipine at 50 mu M inhibited almost completely the high K+-in duced [Ca2+](i) transient. Consequently, it was demonstrated in the pr esent study that nimodipine and nitrendipine inhibit both L- and N-typ e calcium channels and thus seem to be unique among the dihydropyridin es examined in their effects on calcium channels in dibutyryl cAMP-dif ferentiated neuroblastoma x glioma hybrid NG 108-15 cells, whereas nif edipine and niguldipine appear to block mainly L-type calcium channels . (C) 1997 Elsevier Science Ireland Ltd.