AIM: To investigate the possibility of dihydropyridine inhibition of N-type
calcium channels. METHODS: Effects of nifedipine and nicardipine on the hi
gh Kf-induced intracellular Ca2+ concentration ([Ca2+](i)) increase were st
udied by measuring [Ca2+](i) using the fluorescent indicator Fura-2. RESULT
S: Pretreatment of cells with nifedipine 50 mu mol L-l inhibited the high K
+-induced [Ca2+](i) transient by about 60 % (n = 3); however, pretreatment
of cells with nicardipine 10 mu mol.L-1 completely prevented the high Kt-ev
oked [Ca2+](i) increase in dibutyryl cyclic AMP (dbcAMP)-differentiated NG
108-15 cells (n =5). The high K+-induced [Ca2+](i) increase was mediated by
L and N-type voltage-sensitive calcium channels (VSCC) in NC 108-15 cells.
CONCLUSION: Nicardipine at micromolar range inhibited both L- and N-type V
SCC in dbcAMP-differentiated NG 108-15 cells whereas nifedipine mainly inhi
bited L-type calcium channels.