A target K+ channel for the LP-805-induced hyperpolarization in smooth muscle cells of the rabbit portal vein.
The resting membrane potential of smooth muscle cells of the rabbit portal vein was -51.2 mV. LP-805 (8-tert-butyl-6,7-dihydropyrrolo[3,2-e] 5-methylpyrazolo [1,5-a] pyrimidine-3-carbonitrile) hyperpolarized the membrane to -62.3 mV (10 microM) and inhibited the burst spike discharges as measured using the microelectrode method. In dispersed smooth muscle cells, LP-805 (10 microM) generated an outward-current with a maximum amplitude of 68 pA at a holding potential of -40 mV in experiments using the voltage-clamp procedure. The reversal potential of the outward current evoked by LP-805 was -82 mV and this value was close to the equilibrium potential for K+ (-80 mV) in the present ionic conditions, suggesting that LP-805 activated the K+ channel. Generation of both the hyperpolarization and the outward current by LP-805 was inhibited by glibenclamide (> or = 1 microM). Using the cell-attached and cell-free patch-clamp (in the presence of GDP) procedures, the maxi-K+ channel current (150 pS) could be recorded in the absence of LP-805; application of LP-805 additionally opened a small conductance K+ channel current (15 pS) without change in the activity of the maxi-K+ channel. The maxi-K+ channel was sensitive to charybdotoxin (0.1 microM) and to intracellular Ca2+ ([Ca2+]i) concentration. The 15 pS channel was insensitive to [Ca2+]i and charybdotoxin, but sensitive to intracellular ATP concentration. Glibenclamide (> 1 microM) inhibited the 15 pS K+ channel activated by LP-805.(ABSTRACT TRUNCATED AT 250 WORDS)
Kamouchi
M
M
Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Kajioka
S
S
Sakai
T
T
Kitamura
K
K
Kuriyama
H
H
D000818:Animals; D006146:Guanidines / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects*; D020110:Pinacidil; D011169:Portal Vein / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects*; D011720:Pyrazoles / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology*; D011817:Rabbits; D014665:Vasodilator Agents / Q000494:pharmacology*
D006146:Guanidines; D015221:Potassium Channels; D011720:Pyrazoles; D011743:Pyrimidines; D014665:Vasodilator Agents; C073993:8-tert-butyl-6,7-dihydropyrrolo(3,2-e)-5-methylpyrazolo(1,5-a)pyrimidine-3-carbonitrile; D020110:Pinacidil