Abstract
Decarbomethoxylated JW062 (DCJW), the active component of the oxadiazine insecticide (S)-methyl 7-chloro-2,5-dihydro-2-[[(methoxycarbonyl)[4-(trifluoromethoxy)phenyl] amino]carbonyl] indeno[1,2-e][1,3,4]oxadiazine-4a(3H)-carboxylate (DPX-JW062) (indoxacarb), was tested on 2 inward voltage-dependent sodium currents (named INa1 and INa2) expressed in short-term cultured dorsal unpaired median neurons of the cockroach Periplaneta americana. Under whole-cell voltage-clamp conditions, application of DCJW resulted in a biphasic dose-dependent inhibition of the global sodium current amplitude illustrating the differing sensitivity of sodium channels to DCJW. INa2 was less sensitive to DCJW [half-maximal inhibitory concentration (IC50) = 1.6 μM] compared with INa1 (IC50 = 1.7 nM). Although a previous study demonstrated that INa1 was regulated by the cAMP/protein kinase A cascade, we showed that INa2 was mainly regulated in an opposite way by the activation of calcium-calmodulin-dependent protein phosphatase 2B (PP2B) and calcium-calmodulin-dependent protein kinase II (CaM-kinase II). Furthermore, we demonstrated that activation of CaM-kinase II by intracellular calcium via the calcium-calmodulin complex affected the sensitivity of INa2 channels to DCJW. By increasing the intracellular calcium concentration and/or using 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA) (a calcium chelator), N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W7) (a calmodulin inhibitor), cyclosporine A (a PP2B inhibitor), and 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-l-tyrosyl]-4-phenylpiperazine (KN-62) (a CaM-kinase II inhibitor), we revealed that activation of CaM-kinase II was involved in the modulation of the voltage dependence of steady-state inactivation and that the CaM-kinase II pathway activated by elevation of the intracellular calcium concentration might render INa2 channels approximately 3000-fold more sensitive to DCJW. These results indicated that manipulating specific intracellular signaling pathways involved in the regulation of sodium channels might have fundamental consequences for the sensitivity of insects to insecticides. This finding reveals an exciting research area that could lead to improvement in the efficiency of insecticides.
Footnotes
- Received November 11, 2009.
- Accepted January 6, 2010.
B.M. was supported by a doctoral fellowship from the Région Pays de la Loire.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.109.163519.
-
ABBREVIATIONS:
- kdr
- knockdown resistance
- DPX-JW062
- (S)-methyl-7-chloro-2,5-dihydro-2-[[(methoxycarbonyl)[4-(trifluoromethoxy)phenyl]amino]carbonyl]indeno[1,2-e][1,3,4]oxadiazine-4a(3H)-carboxylate
- DCJW
- indoxacarb metabolite decarbomethoxylated JW062
- INa1 and INa2
- inward voltage-dependent sodium currents 1 and 2
- CaM-kinase II
- calcium-calmodulin-dependent protein kinase II
- DUM
- dorsal unpaired median
- TAG
- terminal abdominal ganglion
- IC50
- half-maximal inhibitory concentration
- BAPTA
- 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid
- KN-62
- 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-l-tyrosil]-4-phenylpiperazine (CaM-kinase II inhibitor)
- 4-AP
- 4-aminopyridine
- PKA
- protein kinase A
- CaM
- calmodulin
- W7
- N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (calmodulin inhibitor)
- PP2B
- protein phosphatase 2B.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|