Tertiapin-Q Blocks Recombinant and Native Large Conductance K⁺ Channels in a Use-Dependent Manner

Abstract

Tertiapin, a short peptide from honey bee venom, has been reported to specifically block the inwardly rectifying K ϩ (Kir) channels, including G protein-coupled inwardly rectifying potassium channel (GIRK) 1ϩGIRK4 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 2ϩ -activated large conductance K ϩ channel (BK or MaxiK; ␣-subunit or hSlo1 homomultimers) and mouse inwardly rectifying GIRK1ϩGIRK2 (i.e., Kir3.1 and Kir3.2) heteromultimeric K ϩ channels expressed in Xenopus oocytes and in cultured newborn mouse dorsal root ganglion (DRG) neurons. In twoelectrode voltage-clamped oocytes, tertiapin-Q (1-100 nM) inhibited BK-type K ϩ channels in a use-and concentrationdependent manner. We also confirmed the inhibition of recombinant GIRK1ϩGIRK2 heteromultimers by tertiapin-Q, which had no effect on endogenous depolarization-and hyperpolarization-activated currents sensitive to extracellular divalent cations (Ca 2ϩ , Mg 2ϩ , Zn 2ϩ , and Ba 2ϩ ) in defolliculated oocytes. In voltage-clamped DRG neurons, tertiapin-Q voltageand use-dependently inhibited outwardly rectifying K ϩ currents, but Cs ϩ -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 2ϩ -activated K ϩ channels by tertiapin-Q at nanomolar range via different mechanisms may have implications in pain physiology and therapy.

KATPChannels in the Cardiovascular System

“…Moreover, when heterologously expressed in H9C2 cells (a rat embryonic heart-derived cell line), a ROMK2 construct with a COOH-terminal tag was found to localize to intracellular compartments positive for mitochondrial markers (240). The same study also demonstrated that diazoxide-induced changes in mitochondrial matrix volume and thallium flux into mitochondria are abrogated by tertiapin Q, a peptide isolated from bee toxin that blocks certain types of inwardly rectifying K ϩ channels, including Kir1.x (ROMKx), G protein-activated K ϩ channels (Kir3.x or GIRK1/4) (404,441), and the Ca 2ϩ -activated large-conductance K ϩ channel (BK or MaxiK) (423). Although this result is intriguing, the possibility that ROMK subunits may constitute the pore-forming components of mitochondrial K ATP channels remains to be independently confirmed by other laboratories and with genetic approaches.…”

1-[6-[[(17β)-3-Methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122) Selectively Inhibits Kir3 and BK Channels in a Phospholipase C-Independent Fashion

“…First, unlike U73122, tertiapin is also an equally potent blocker of Kir1 channels (Jin and Lu, 1998). Second, in contrast to the inhibitory effect of U73122, block of BK channels by tertiapin is slow and use-dependent requiring strong and prolonged depolarization to develop (Kanjhan et al, 2005). Thus, tertiapin (300 nM) did not produce any suppression of BK channels when we used the same recording conditions that reliably revealed the blocking action of U73122 (physiological K ϩ gradient, V h , 0 mV; data not shown).…”

“…Tertiapin was introduced as a specific and potent blocker of Kir3 channels at nanomolar affinity, whereas Kir2 channels remained insensitive (Jin and Lu, 1998). More recently, tertiapin was also found to inhibit BK channels (Kanjhan et al, 2005). Its mechanism of action is not fully resolved, but tertiapin is thought to occlude the channel by plugging its ␣ helix into the external vestibule of the ion conduction pore (Jin et al, 1999).…”

Conopeptide Vt3.1 Preferentially Inhibits BK Potassium Channels Containing β4 Subunits via Electrostatic Interactions

“…Previous studies have identified peptide toxins that modulate BK channels from venoms of various animals including scorpion (28 -30), cone snail (31), snake (32), bee (33), and spider (34). Among these toxins, charybdotoxin (ChTx) and iberiotoxin (IbTx) have been intensively studied for molecular pharmacology and used as an effective tool to identify BK channels in various tissues that contributed greatly in the understanding (Fig.…”