Noradrenaline-activated heparin-sensitive Ca2+ entry after depletion of intracellular Ca2+ store in portal vein smooth muscle cells.
Single portal vein smooth muscle cells were voltage-clamped using the whole cell patch-clamp technique. Intracellular free Ca2+ concentration ([Ca2+]i) was simultaneously monitored using the fluorescence from the dye indo-1. Noradrenaline (NA, 10 microM) evoked a transient increase in [Ca2+]i, due to inositol 1,4,5-trisphosphate (InP3)-induced Ca2+ release, followed by a sustained increase in [Ca2+]i, caused by extracellular Ca2+ entry. This phase was maintained as long as NA was present and was never observed when the agonist was only briefly applied (3 s). Neither ryanodine, nor caffeine produced the Ca2+ influx whereas the complete depletion of intracellular Ca2+ pool in the absence of external Ca2+ allowed, when Ca2+ was readmitted, the activation of the Ca2+ entry which was used to replenish Ca2+ store. During NA stimulation, the Ca2+ entry was activated even if the Ca2+ pool had not been totally emptied. The Ca2+ entry pathway involved was blocked by Ni2+ and Mn2+, was not permeable to these ions, and was more sensitive to heparin than the InsP3-induced Ca2+ release. Thus, the complete depletion of Ca2+ store activates a Ca2+ influx which is modulated by NA such as in its presence, a partial depletion is enough to induce Ca2+ entry.
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, URA Centre National de la Recherche Scientifique 1489, Université de Bordeaux II, France.
P
P
Pacaud
G
G
Loirand
G
G
Grégoire
C
C
Mironneau
J
J
Mironneau
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology*; D066298:In Vitro Techniques; D008345:Manganese / Q000494:pharmacology; D008564:Membrane Potentials; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009532:Nickel / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D011169:Portal Vein; D051381:Rats; D017208:Rats, Wistar; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology
D011942:Receptors, Adrenergic, alpha; D012433:Ryanodine; D002110:Caffeine; D008345:Manganese; D009532:Nickel; D006493:Heparin; D000109:Acetylcholine; D002118:Calcium; D009638:Norepinephrine