The effects of caffeine on ATP-sensitive K(+) channels in smooth muscle cells from pig urethra.
The effects of caffeine on both levcromakalim-induced macroscopic and unitary currents in pig proximal urethra were investigated by the use of patch-clamp techniques (conventional whole-cell configuration and cell-attached configuration). The effects of caffeine were also examined on currents in inside-out patches of COS7 cells expressing carboxy terminus truncated inwardly rectifying K(+) channel (Kir6.2) subunits (i.e. Kir6.2DeltaC36) which form ATP-sensitive K(+) channels (K(ATP) channels). In conventional whole-cell configuration, the levcromakalim (100 microM)-induced inward current (symmetrical 140 mM K(+) conditions) was inhibited by caffeine (> or =1 mM) at a holding potential of -50 mV. In contrast, ryanodine (10 microM) caused no significant inhibitory effect on the gradual decay of the levcromakalim-induced current at -50 mV. The amplitude of the 30 microM levcromakalim-induced current was enhanced by 3-isobutyl-1-methylxanthine (IBMX, 100 microM). In cell-attached configuration, the levcromakalim-induced K(+) channel openings were inhibited by subsequent application of 10 mM caffeine, decreasing the channel open probability at -50 mV. Reverse transcriptase-polymerase chain reaction (RT - PCR) analysis revealed the presence of Kir6.2 transcript in pig urethra. Caffeine (> or =3 mM) inhibited the channel activity of Kir6.2DeltaC36 expressed in COS7 cells (3 mM caffeine, 65+/-6%, n=4; 10 mM caffeine, 29+/-2%, n=4). These results suggest that caffeine can inhibit the activity of K(ATP) channels through a direct blocking effect on the pore-forming Kir subunit.
Teramoto
N
N
Department of Pharmacology, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi Ward, Fukuoka, 812-8582, Japan. noritera@linne.med.kyushu-u.ac.jp
Yunoki
T
T
Tanaka
K
K
Takano
M
M
Masaki
I
I
Yonemitsu
Y
Y
Sueishi
K
K
Ito
Y
Y
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D018528:ATP-Binding Cassette Transporters; D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D019806:Cromakalim / Q000494:pharmacology; D004347:Drug Interactions; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D054086:KATP Channels; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying; D012433:Ryanodine / Q000494:pharmacology; D013552:Swine; D014521:Urethra / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D014530:Uridine Diphosphate / Q000494:pharmacology
D018528:ATP-Binding Cassette Transporters; D000697:Central Nervous System Stimulants; D054086:KATP Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; C092520:uK-ATP-1 potassium channel; D019806:Cromakalim; D012433:Ryanodine; D002110:Caffeine; D004533:Egtazic Acid; D014530:Uridine Diphosphate; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D005905:Glyburide; D015056:1-Methyl-3-isobutylxanthine