Single channel and whole-cell K-currents evoked by levcromakalim in smooth muscle cells from the rabbit portal vein.
1. Single channel and whole-cell current recordings were made from single smooth muscle cells isolated from the rabbit portal vein. 2. Application of 10 microM levcromakalim ((-)-Ckm) to single cells held with pipettes containing 1 mM GDP induced a K-current (IK(Ckm)) which occurred in addition to the current caused by GDP alone (IK(GDP)) and averaged 135 pA at -37 mV. We have investigated whether the same K channels underlie the GDP- and Ckm-induced K-currents. 3. If 1 mM GDP was in the pipette but Mg ions were omitted the effect of GDP was absent and IK(Ckm) averaged only 10 pA, suggesting that the action of (-)-Ckm was Mg-dependent. 4. Intracellular ATP was not observed to have much effect on IK(-Ckm). Loading of cells with 10 mM ATP from the recording pipette had no significant effect and flash photolysis of caged-ATP loaded into cells from the pipette, estimated to release about 1 mM free ATP, also had no effect on IK(-Ckm). 5. Bath-applied glibenclamide inhibited IK(-Ckm) with an IC50 of 200 nM, a value 8 times higher than that found for inhibition of IK(GDP). The delayed rectifier K-current (IK(DR)) was also inhibited by glibenclamide but at higher concentrations (IC50 100 microM). Bath-applied tetraethylammonium ions (TEA) inhibited IK(-Ckm) and IK(GDP) to the same extent (IC50 about 7 mM). 6. In inside-out patch recordings (- )-Ckm (10 microM) applied to the intracellular surface of the membrane potentiated the opening of K channels already stimulated by I mM GDP and all of the channel activity was abolished by 10 microM glibenclamide. The unitary conductance of the channels was 24lpS in a 60 mM: 130 mM K-gradient.7. We suggest that (-)-Ckm may hyperpolarize and relax smooth muscle cells by opening KNDP, a class of small conductance K channels that are related to the ATP-sensitive K channels seen in other tissues.
Beech
D J
DJ
Department of Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School, London.
Zhang
H
H
Nakao
K
K
Bolton
T B
TB
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001578:Benzopyrans / Q000494:pharmacology*; D019806:Cromakalim; D005905:Glyburide / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011169:Portal Vein / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects*; D011758:Pyrroles / Q000494:pharmacology*; D011817:Rabbits; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology*
D001578:Benzopyrans; D015221:Potassium Channels; D011758:Pyrroles; D013757:Tetraethylammonium Compounds; D014665:Vasodilator Agents; D019806:Cromakalim; D006153:Guanosine Diphosphate; D000255:Adenosine Triphosphate; D008274:Magnesium; D005905:Glyburide