J Pharmacol Exp Ther 2005 Sep 01;3143:1353-61. doi: 10.1124/jpet.105.085928.

Tertiapin-Q blocks recombinant and native large conductance K+ channels in a use-dependent manner.

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Tertiapin, a short peptide from honey bee venom, has been reported to specifically block the inwardly rectifying K(+) (Kir) channels, including G protein-coupled inwardly rectifying potassium channel (GIRK) 1+GIRK4 heteromultimers and ROMK1 homomultimers. In the present study, the effects of a stable and functionally similar derivative of tertiapin, tertiapin-Q, were examined on recombinant human voltage-dependent Ca(2+)-activated large conductance K(+) channel (BK or MaxiK; alpha-subunit or hSlo1 homomultimers) and mouse inwardly rectifying GIRK1+GIRK2 (i.e., Kir3.1 and Kir3.2) heteromultimeric K(+) channels expressed in Xenopus oocytes and in cultured newborn mouse dorsal root ganglion (DRG) neurons. In two-electrode voltage-clamped oocytes, tertiapin-Q (1-100 nM) inhibited BK-type K(+) channels in a use- and concentration-dependent manner. We also confirmed the inhibition of recombinant GIRK1+GIRK2 heteromultimers by tertiapin-Q, which had no effect on endogenous depolarization- and hyperpolarization-activated currents sensitive to extracellular divalent cations (Ca(2+), Mg(2+), Zn(2+), and Ba(2+)) in defolliculated oocytes. In voltage-clamped DRG neurons, tertiapin-Q voltage- and use-dependently inhibited outwardly rectifying K(+) currents, but Cs(+)-blocked hyperpolarization-activated inward currents including I(H) were insensitive to tertiapin-Q, baclofen, barium, and zinc, suggesting absence of functional GIRK channels in the newborn. Under current-clamp conditions, tertiapin-Q blocked the action potential after hyperpolarization (AHP) and increased action potential duration in DRG neurons. Taken together, these results demonstrate that the blocking actions of tertiapin-Q are not specific to Kir channels and that the blockade of recombinant BK channels and native neuronal AHP currents is use-dependent. Inhibition of specific types of Kir and voltage-dependent Ca(2+)-activated K(+) channels by tertiapin-Q at nanomolar range via different mechanisms may have implications in pain physiology and therapy.

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Species referenced: Xenopus laevis
Genes referenced: drg1 kcnj1 kcnj3 kcnma1