The nonpeptide alpha-eudexp6l from Juniperus virginiana Linn. (Cupressaceae) inhibits omega-agatoxin IVA-sensitive Ca2+ currents and synaptosomal 45Ca2+ uptake.
Recently, the omega-agatoxin IVA (omega-Aga-IVA)-sensitive Ca2+ channel has been demonstrated to play an important role in the physiological neurotransmitter release in mammalian nerve terminals. In this study, we demonstrate that alpha-eudesmol from Juniperus virginiana Linn. (Cupressaceae) inhibits omega-Aga-IVA-sensitive Ca2+ channels in rat brain synaptosomes and cerebellar Purkinje cells. Thirty millimolar KCl-induced 45Ca2+ uptake into the synaptosomes was inhibited by omega-Aga-IVA but insensitive to omega-conotoxin GVIA (omega-CTX-GVIA, N-type Ca2+ channel blocker) and nicardipine (L-type Ca2+ channel blocker). We found that alpha-eudesmol concentration-dependently inhibited the above synaptosomal 45Ca2+ uptake with an IC50 value of 2.6 microM. Co-treatment with alpha-eudesmol and omega-Aga-IVA did not cause any additive inhibitory effect against the synaptosomal 45Ca2+ uptake. Using the whole-cell patch clamp electrophysiological technique, we further demonstrated that alpha-eudesmol concentration-dependently inhibited omega-Aga-IVA-sensitive Ca2+ channel currents recorded from Purkinje cells with an IC50 value of 3.6 microM. The current-voltage relationship of the omega-Aga-IVA-sensitive Ca2+ channel currents was not changed by alpha-eudesmol. On the other hand, alpha-eudesmol also displayed an inhibitory effect on N-type Ca2+ channel currents recorded from differentiated NG108-15 cells with an IC50 value of 6.6 microM. However, alpha-eudesmol had little inhibitory effect on L-type Ca2+ channel currents. Thus, the present data indicated that alpha-eudesmol is a potent nonpeptidergic compound which blocks the presynaptic omega-Aga-IVA-sensitive Ca2+ channel with relative selectivity.
Asakura
K
K
Discovery Research Laboratories, Shionogi, 3-1-1, Futaba-cho, Toyonaka, Osaka, 561-0825, Japan.
Kanemasa
T
T
Minagawa
K
K
Kagawa
K
K
Ninomiya
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type; D002132:Calcium Radioisotopes; D004553:Electric Conductivity; D018653:Juniperus / Q000737:chemistry; D010936:Plant Extracts / Q000494:pharmacology*; D011689:Purkinje Cells / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D045787:Sesquiterpenes, Eudesmane; D013111:Spider Venoms / Q000494:pharmacology*; D013574:Synaptosomes / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000378:metabolism; D020867:omega-Agatoxin IVA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002132:Calcium Radioisotopes; D010936:Plant Extracts; D045787:Sesquiterpenes, Eudesmane; D013111:Spider Venoms; D013729:Terpenes; D020867:omega-Agatoxin IVA; C118684:alpha-eudesmol; D002118:Calcium