GTP-binding proteins mediate noradrenaline effects on calcium and chloride currents in rat portal vein myocytes.
1. Membrane currents were recorded by a patch-clamp pipette technique in cultured cells from rat portal vein using the whole-cell mode. 2. Noradrenaline (NA, 10(-5) M) and phorbol-12,13-dibutyrate (PDBu, 10(-7) M) produced an increase in voltage-dependent inward current carried by barium (5 mM), but their effects were not additive. Calcium-activated chloride current was evoked by NA but not by PDBu. 3. The NA-induced increase in peak voltage-dependent inward current was inhibited by intracellular application of GDP-beta-S (10(-3) M) while the effect of PDBu was unchanged. GDP-beta-S blocked the NA-induced chloride current but had no effect on the caffeine-induced chloride current. 4. Inclusion of GTP-gamma-S (10(-5)-10(-4) M) in the pipette solution increased the voltage-dependent inward current and inhibited the NA- or PDBu-induced increase in peak current. GTP-gamma-S potentiated the effect of NA on calcium-activated chloride current. At higher concentrations (10(-3) M), GTP-gamma-S activated the chloride current and prevented the effects of NA or caffeine on this current. 5. The combination of 10(-5) M-aluminium chloride and 10(-2) M-sodium fluoride had an effect similar to that of high concentrations of GTP-gamma-S on both inward current and calcium-activated chloride current. In contrast, arachidonic acid (10(-3) M) had no effect on calcium and chloride conductances activated by NA. 6. Cells responded normally to NA after pre-treatment for 4-30 h with 10 micrograms ml-1 pertussis toxin (PTx). 7. It is concluded that the stimulation of calcium and chloride conductances by NA is mediated through activation of a PTx-insensitive GTP-binding protein. This effect may involve activation of phospholipase C enzyme and production of both D-myo-inositol 1,4,5-trisphosphate which depletes calcium stores and diacylglycerol which activates protein kinase C.
Loirand
G
G
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, INSERM JF, Bordeaux, France.
Pacaud
P
P
Mironneau
C
C
Mironneau
J
J
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D002478:Cells, Cultured; D018118:Chloride Channels; D004553:Electric Conductivity / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects; D008565:Membrane Proteins / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology*; D011169:Portal Vein / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains
D015220:Calcium Channels; D018118:Chloride Channels; D007473:Ion Channels; D008565:Membrane Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins; D009638:Norepinephrine