Modulation of [3H]dihydropyridine binding by activation of protein kinase C in vascular smooth muscle.
The influence of noradrenaline and protein kinase C modulators on (+)-[3H]isradipine binding to voltage-dependent calcium channels has been studied in membranes of equine portal vein smooth muscle and intact strips isolated from rat portal vein. Specific (+)-[3H]isradipine binding to intact strips was increased by noradrenaline, a combination of aluminium and fluoride, and phorbol esters. The increase in isradipine binding induced by noradrenaline was inhibited by 1 microM prazosin while that induced by phorbol esters was inhibited by H7 (a protein kinase C inhibitor). In strips pretreated 6 h with 10 micrograms.ml-1 pertussis toxin, the noradrenaline-induced increase in isradipine binding was unchanged. In contrast, isradipine binding to membranes was unaffected by noradrenaline or GTP-gamma-S. Only phorbol esters had a stimulatory effect on isradipine binding when membranes were incubated in a medium containing 10 microM ATP and 5 mM Mg2+. Scatchard plot analysis reveals that the stimulation of isradipine binding by both noradrenaline and phorbol esters appears to result from a decrease in KD rather than an effect on the maximal binding capacity. Contractions evoked by noradrenaline were concentration-dependently depressed by isradipine. About 30% of the response was resistant to inhibition, while KCl-induced contractions were completely blocked. However, noradrenaline-induced contractions were more sensitive to isradipine inhibition than were KCl-induced contractions. These results suggest that activation of protein kinase C modulates isradipine binding to voltage-dependent Ca2+ channels independently of a separate modulation by membrane depolarization.
Mironneau
C
C
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, Université de Bordeaux II, INSERM CJF 88-13, France.
Rakotoarisoa
L
L
Sayet
I
I
Mironneau
J
J
D000535:Aluminum / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D004095:Dihydropyridines / Q000378:metabolism*; D004789:Enzyme Activation; D005461:Fluorine / Q000494:pharmacology; D006736:Horses; D066298:In Vitro Techniques; D017275:Isradipine; D008564:Membrane Potentials / Q000187:drug effects; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000201:enzymology*; D009638:Norepinephrine / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D010766:Phosphorylation; D011169:Portal Vein / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism*; D014316:Tritium
D015220:Calcium Channels; D004095:Dihydropyridines; D010703:Phorbol Esters; D014316:Tritium; C053629:fluoroaluminum; D005461:Fluorine; D011189:Potassium Chloride; C038806:1,4-dihydropyridine; D000535:Aluminum; D011493:Protein Kinase C; D009638:Norepinephrine; D017275:Isradipine