Abstract
Our recent study has revealed that 12,14-dichlorodehydroabietic acid (diCl-DHAA), which is synthetically derived from a natural product, abietic acid, is a potent opener of large conductance Ca2+-activated K+ (BK) channel. Here, we examined, by using a channel expression system in human embryonic kidney 293 cells, the mechanisms underlying the BK channel opening action of diCl-DHAA and which subunit of the BK channel (α or β1) is the site of action for diCl-DHAA. BK channel activity was significantly enhanced by diCl-DHAA at concentrations of 0.1 μM and higher in a concentration-dependent manner. diCl-DHAA enhanced the activity of BKα by increasing sensitivity to both Ca2+ and membrane potential without changing the single channel conductance. It is notable that the increase in BK channel open probability by diCl-DHAA showed significant inverse voltage dependence, i.e., larger potentiation at lower potentials. Since coexpression of β1 subunit with BKα did not affect the potency of diCl-DHAA, the site of action for diCl-DHAA is suggested to be BKα subunit. Moreover, kinetic analysis of single channel currents indicates that diCl-DHAA opens BKα mainly by decreasing the time staying in a long closed state. Although reconstituted voltage-dependent Ca2+ channel current was significantly reduced by 1 μM diCl-DHAA, BK channels were selectively activated at lower concentrations. These results indicate that diCl-DHAA is one of the most potent BK channel openers acting on BKα and a useful prototype compound to develop a novel BK channel opener.
Footnotes
-
doi:10.1124/jpet.105.093856.
-
ABBREVIATIONS: BK, large conductance Ca2+-activated K+; [Ca2+]i, intracellular Ca2+ concentration; BMS-204352, (3S)-(+)-(5-chloro-2-methoxyphenyl)-1,3-dihydro-3-fluoro-6-(trifluoromethyl)-2H-indole-2-one; L-735,334, 14-hedroxy 8-daucene-3,4-diol oleate; diCl-DHAA, 12,14-dichlorodehydroabietic acid; CaV, voltage-dependent Ca2+; HEK, human embryonic kidney; I-V, current-voltage; SK, small conductance Ca2+-activated K+; IK, intermediate conductance Ca2+-activated K+; CGS-7181, ethyl 2-hydroxy-1-[[(4-methylphenyl)amino]oxo]-6-trifluoromethyl-1H-indole-3-carboxylate; CGS-7184, ethyl 1-[[(4-chlorophenyl)amino]oxo]-2-hydroxy-6-trifluoromethyl-1H-indole-3-carboxylate; NS-1608, N-(3-(trifluoromethyl)phenyl)-N′-(2-hydroxy-5-chlorophenyl)urea; NS-1619, 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one; NS-8, 2-amino-3-cyano-5-(2-fluorophenyl)-4-methylpyrrole.
- Received August 4, 2005.
- Accepted September 28, 2005.
- 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.
|
