Participation of calcium, released from the IP3-sensitive Ca-store in activation of Ca-dependent potassium conductance of ileal smooth muscle cells.
The apamin-, charybdotoxin- (CTX) and glibenclamide- (GLB) sensitive components, which form the active part of the net potassium outward current (IK) in single smooth muscle cells from the longitudinal layer of guinea-pig ileum (LC), were investigated for their sensitivity to calcium. The experiments were carried out by the whole-cell voltage-clamp method. A successful block of all Ca-sources (with heparin and nifedipine; heparin and cyclopiazonic acid while the intracellular Ca-concentration--[Ca2+]i--was kept at 3 x 10(-8) mol/l by 11 mmol/l EGTA into the pipette solution) led to the complete inhibition of IK. The deeply located Ca-sensitive Ca-pool was effectively isolated by the high concentration of the chelator, which was proved by the fact that ruthenium red and ryanodine failed to affect IK. The GLB-sensitive component of IK demonstrated Ca-gated properties, while both the other components were activated most probably by calcium, released form the IP3-sensitive Ca-pool. It was concluded that the IP3-induced Ca-release mechanism plays an important role in the regulation of K(+)-conductivity in LC.
Gagov
H S
HS
Institute of Physiology, Bulgarian Academy of Sciences, Sofia.
Duridanova
D B
DB
Boev
K K
KK
D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D018999:Charybdotoxin; D004533:Egtazic Acid / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D006168:Guinea Pigs; D006493:Heparin / Q000494:pharmacology; D007082:Ileum / Q000502:physiology*; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D012430:Ruthenium Red / Q000494:pharmacology; D012604:Scorpion Venoms / Q000494:pharmacology
D007211:Indoles; D015221:Potassium Channels; D012604:Scorpion Venoms; D012430:Ruthenium Red; D018999:Charybdotoxin; D001030:Apamin; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D009543:Nifedipine; D005905:Glyburide; D002118:Calcium; C000543:cyclopiazonic acid