Peroxynitrite affects Ca2+ influx through voltage‐dependent calcium channels

The effect of peroxynitrite (OONO−) on voltage‐dependent Ca2+ channels (VDCCs) was examined by measuring [45Ca2+] influx into mouse cerebral cortical neurones. OONO− time‐ and dose‐dependently increased [45Ca2+] influx and this increase was abolished by manganese (III) tetrakis (4‐benzoic acid) porphyrin, a scavenger for OONO−. Inhibition of cyclic GMP (cGMP) formation did not alter the OONO−‐induced [45Ca2+] influx. OONO−, as well as 30 mm KCl, significantly increased fluorescence intensity of cell‐associated bis‐(1,3‐dibutylbarbituric acid) trimethine oxonol (bis‐oxonol). Tetrodotoxin and membrane stabilizers such as lidocaine dose‐dependently suppressed OONO−‐induced [45Ca2+] influx. Although each of 1 µm nifedipine and 1 µmω‐agatoxin VIA (ω‐ATX) significantly inhibited the OONO−‐induced [45Ca2+] influx and the concomitant presence of these agents completely abolished the influx, 1 µmω‐conotoxin GVIA (ω‐CTX) showed no effect on the influx. On the other hand, OONO− itself reduced 30 mm KCl‐induced [45Ca2+] influx to the level of [45Ca2+] influx induced by OONO− alone, and the magnitude of this reduction was as same as that of KCl‐induced [45Ca2+] influx by ω‐CTX. These results indicate that OONO− increases [45Ca2+] influx into the neurones through opening P/Q‐ and L‐type VDCCs subsequent to depolarization, and inhibits the influx through N‐type VDCCs.