Tertiapin potently and selectively blocks muscarinic K(+) channels in rabbit cardiac myocytes.
Tertiapin is a 21-residue peptide isolated from honey bee venoms. A recent study indicated that tertiapin is a potent blocker of certain types of inwardly rectifying K(+) (Kir) channels (). We examined the effect of tertiapin on ion channel currents in rabbit cardiac myocytes using the patch-clamp technique. In the whole-cell configuration, tertiapin fully inhibited acetylcholine (1 microM)-induced muscarinic K(+) (K(ACh)) channel currents in atrial myocytes with the half-maximum inhibitory concentration of approximately 8 nM through approximately 1:1 stoichiometry. The potency of tertiapin in inhibiting K(ACh) channels was not significantly different at -40 and -100 mV. Tertiapin also inhibited the K(ACh) channel preactivated by intracellular guanosine 5'-O-(3-thiotriphosphate), a nonhydrolyzable GTP analog. A constitutively active Kir channel, the I(K1) channel, was at least 100 times less sensitive to tertiapin. Another Kir channel in cardiac myocytes, the ATP-sensitive K(+) channel, was virtually insensitive to tertiapin (1 microM). The voltage-dependent K(+) and the L-type Ca(2+) channels were not affected by tertiapin (1 microM). At the single-channel level, tertiapin inhibited the K(ACh) channel from the outside of the membrane by reducing the NP(o) (N is the number of functional channels, and the P(o) is the open probability of each channel) without affecting the single-channel conductance or fast kinetics. Therefore, tertiapin potently and selectively blocks the K(ACh) channel in cardiac myocytes in a receptor- and voltage-independent manner. Tertiapin is a novel pharmacological tool to identify the functional role of the K(ACh) channel in the parasympathetic regulation of the heart beat.
Kitamura
H
H
Department of Cardiac Physiology, National Cardiovascular Center Research Institute, Suita, Osaka, Japan.
Yokoyama
M
M
Akita
H
H
Matsushita
K
K
Kurachi
Y
Y
Yamada
M
M
D018528:ATP-Binding Cassette Transporters; D000595:Amino Acid Sequence; D000818:Animals; D001514:Bee Venoms / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects; D002469:Cell Separation; D004594:Electrophysiology; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D054086:KATP Channels; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000187:drug effects; D024661:Potassium Channels, Inwardly Rectifying; D011817:Rabbits; D011976:Receptors, Muscarinic / Q000187:drug effects*
D018528:ATP-Binding Cassette Transporters; D001514:Bee Venoms; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D054086:KATP Channels; D018727:Muscarinic Antagonists; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011976:Receptors, Muscarinic; C092520:uK-ATP-1 potassium channel; C029738:tertiapin