Functional significance of nitric oxide in ionomycin-evoked [3H]GABA release from mouse cerebral cortical neurons.
We investigated a role of nitric oxide (NO) on ionomycin-evoked [3H]GABA release using mouse cerebral cortical neurons. lonomycin dose-dependently released [3H]GABA up to 1 microM. The extent of the release by 0.1 microM ionomycin was in a range similar to that by 30 mM KCl. The ionomycin (0.1 microM)-evoked [3H]GABA release was dose-dependently inhibited by NO synthase inhibitors and hemoglobin, indicating that the ionomycin-evoked [3H]GABA release is mediated through NO formation. The inhibition of cGMP formation by 1H-[1,2,4] oxodizao [4,3-a] quinoxalin-1-one (ODQ), a selective inhibitor for NO-sensitive guanylate cyclase, showed no affects on the ionomycin-evoked [3H]GABA release. Tetrodotoxin and dibucaine significantly suppressed the ionomycin-evoked [3H]GABA release and ionomycin increased fluorescence intensity of bis-oxonol, suggesting the involvement of membrane depolarization in this release. The ionomycin-evoked [3H]GABA release was maximally reduced by about 50% by GABA uptake inhibitors. The concomitant presence of nifedipine and omega-agatoxin VIA (omega-ATX), inhibitors for L- and P/Q-type voltage-dependent calcium channels, respectively, caused the reduction in the ionomycin-evoked release by about 50%. The simultaneous addition of nifedipine, omega-ATX and nipecotic acid completely abolished the release. Although ionomycin released glutamate, (+)-5-methyl-1-,11-dihydro-5H-dibenzo-[a,d]cycloheptan-5,10-imine (MK-801) and 6,7-dinitroquinoxaline-2,3-dione (DNQX) showed no effects on the ionomycin-induced [3H]GABA release. Based on these results, it is concluded that NO formed by ionomycin plays a critical role in ionomycin-evoked [3H]GABA release from the neurons.
Katsura
Masashi
M
Department of Pharmacology, Kawasaki Medical School, Matsushima, Kurashiki, Japan.
Shuto
Keijiro
K
Mohri
Yutaka
Y
Shigeto
Makoto
M
Ohkuma
Seitaro
S
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D002540:Cerebral Cortex; D006152:Cyclic GMP / Q000378:metabolism / Q000494:pharmacology; D003992:Dibucaine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018682:GABA Agents / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D006454:Hemoglobins / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D013779:Tetrodotoxin / Q000494:pharmacology; D013858:Thiobarbiturates / Q000032:analysis / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D018682:GABA Agents; D006454:Hemoglobins; D007476:Ionophores; D013858:Thiobarbiturates; D009569:Nitric Oxide; D018698:Glutamic Acid; D013779:Tetrodotoxin; C025284:bis(1,3-diethylthiobarbiturate)trimethineoxonol; D005680:gamma-Aminobutyric Acid; D015759:Ionomycin; D007770:L-Lactate Dehydrogenase; D019001:Nitric Oxide Synthase; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D008274:Magnesium; D003992:Dibucaine