The effects of nifedipine, niguldipine, nimodipine and nitrendipine on the high 
K+-induced intracellular Ca2+ ([Ca2+]i) transient in dibutyryl 
cAMP-differentiated neuroblastoma x glioma hybrid NG 108-15 cells were studied 
by using the fluorescent Ca2+ indicator fura-2. It was observed that nifedipine 
at the concentration of 50 microM inhibited the high K+-induced [Ca2+]i 
transient by about 60%; niguldipine at the concentration of 10 microM caused a 
reduction of about 65% in the high K+-induced calcium signal and a further 
increase in the concentration up to 50 microM did not result in a significant 
further reduction in the high K+-induced calcium signal. However, on the other 
hand, nimodipine and nitrendipine at 50 microM inhibited almost completely the 
high K+-induced [Ca2+]i transient. Consequently, it was demonstrated in the 
present study that nimodipine and nitrendipine inhibit both L- and N-type 
calcium channels and thus seem to be unique among the dihydropyridines examined 
in their effects on calcium channels in dibutyryl cAMP-differentiated 
neuroblastoma x glioma hybrid NG 108-15 cells, whereas nifedipine and 
niguldipine appear to block mainly L-type calcium channels.