L-type calcium channels may fill directly the IP3-sensitive calcium store.
The relationship between inositol-1,4,5-trisphosphate-sensitive Ca2+ stores and Ca2+ entry through potential-dependent L-type Ca2+ channels was examined using whole-cell voltage-clamp technique in cells of longitudinal muscle layer of guinea-pig ileum. It was found that heparin (10(-10) mol/l) in the pipette rapidly inhibited the current through L-type Ca2+ channels. Neither an inhibitor of the sarcoplasmic reticulum Ca2+ pump (cyclopiazonic acid) nor blockers of Ca(2+)-induced Ca2+ release (ryanodine or ruthenium red) affected the Ca2+ current. The failure of heparin to affect Ca(2+)-currents through L-type Ca2+ channels in cells from circular muscle of the same organ suggested that heparin had no direct effect on L-type Ca2+ channels. Thus the inhibition of the latter in heparin-loaded cells from the longitudinal layer is supposed to be Ca(2+)-dependent due to the overfilling of the inositol-1,4,5-trisphosphate-sensitive Ca2+ store.
Gagov
H S
HS
Institute of Physiology, Bulgarian Academy of Sciences, Sofia.
Duridanova
D B
DB
Boev
K K
KK
Daniel
E E
EE
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000145:classification / Q000187:drug effects / Q000378:metabolism*; D006168:Guinea Pigs; D006493:Heparin / Q000378:metabolism / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007424:Intracellular Fluid / Q000378:metabolism; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012430:Ruthenium Red / Q000494:pharmacology
D015220:Calcium Channels; D012430:Ruthenium Red; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D009543:Nifedipine; D011188:Potassium; D002118:Calcium