Long-term exposure to nicotine induces up-regulation of L-type voltage-dependent calcium channels in mouse cerebrocortical neurons *
The effects of long-term (72 hours) exposure to a low concentration (0.1 μM) of nicotine on various types of voltage-dependent Ca2+ channels (VDCCs) and neuronal nicotinic acetylcholine receptors (nnAChRs) were examined using primary cultures of mouse cerebral cortical neurons. Thirty milimolar KC1 stimulated [45 Ca2+] influx into the neurons increased with increase in the duration of nicotine exposure and its concentrations. The maximal increase of KC1-stimulated [45 Ca 2+] influx was observed 24 hours after the initiation of exposure and thereafter was maintained up to 72 hours, at which time it was completely suppressed by mecamylamine, an inhibitor for nnAChRs. The KC1-induced [45 Ca2+] influx observed after long-term exposure to nicotine, which was sensitive to nifedipine, an inhibitor of L-type VDCCs, was facilitated while the [45 Ca2+] influx through P/Q-and N-type VDCCs showed no changes. Moreover, enhanced immunoreactivity against antibodies for α1C, α1D and α2/б1, subunits of L-type VDCCs was recognized, whereas no changes in immunoreactivity against antibodies for α1A and α1B subunits of other types of VDCCs were noted. In addition, the expression of mRNA for L-type VDCC subunit, α1F, was also enhanced, although β4 mRNA expression did not change. Up-regulation of α4 and β2 subunits, but not α3 subunit of nnAChRs, was also noted after the nicotine exposure. Taken together, these results indicate that long-term exposure of the neurons to a low concentration of nicotine induces both increased [45 Ca 2+] influx through up-regulated L-type VDCCs and nnAChR up-regulation. (Accepted on February 26, 2002) Kawasaki Igakkaishi 28(1) : 43-58, 2002
