Membrane-delimited G protein-mediated coupling between V1a vasopressin receptor and dihydropyridine binding sites in rat glomerulosa cells.
In rat glomerulosa cells, vasopressin stimulates intracellular calcium mobilization via at least two distinct mechanisms: the release of calcium from inositol-1,4,5-P3-sensitive stores and the activation of transmembrane calcium influx. In this study, we focused on the second mechanism through three experimental approaches. By videomicroscopically examining Fura-2-loaded cells, we demonstrate that vasopressin induces a dose-dependent and receptor-mediated calcium influx fully inhibited by either 1 microM nifedipine or a pertussis toxin pretreatment and potentiated by 1 microM BAY K 8644. Patch-clamp experiments also indicate that vasopressin stimulates L-type calcium current by 87% and only weakly inhibits T-type calcium current. To further characterize the coupling between the vasopressin receptor and the dihydropyridine calcium channel, we performed binding studies using tritiated nitrendipine. With this technique, we showed that on intact cells, vasopressin is able to increase the specific binding of tritiated nitrendipine in a dose-dependent manner (Kact = 2 nM). Pharmacological studies using a series of vasopressin analogs revealed that this effect is mediated via a V1a vasopressin receptor subtype. Furthermore, the vasopressin-stimulated nitrendipine binding was sensitive to pertussis toxin pretreatment, which affected only the maximum binding capacity of nitrendipine-binding sites. More interestingly, we demonstrate that vasopressin still increases nitrendipine binding to plasma membrane preparation and that GTP is absolutely necessary for such a hormonal effect. Altogether, these data confirm the existence of a tight and direct coupling between the V1a vasopressin receptor and a dihydropyridine calcium channel via a pertussis toxin-sensitive G protein.
Centre National de la Recherche Scientifique, Institute National de la Santé et de la Recherche Médicale de Pharmacologie/Endocrinologie U 401, Montpellier, France.
E
E
Grazzini
T
T
Durroux
M D
MD
Payet
L
L
Bilodeau
N
N
Gallo-Payet
G
G
Guillon
D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism / Q000494:pharmacology; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D002121:Calcium Channel Blockers / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D020746:Calcium Channels, L-Type; D002478:Cells, Cultured; D005260:Female; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000494:pharmacology; D008566:Membranes / Q000378:metabolism; D009568:Nitrendipine / Q000378:metabolism; D037342:Pertussis Toxin; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017483:Receptors, Vasopressin / Q000187:drug effects / Q000378:metabolism*; D012680:Sensitivity and Specificity; D014316:Tritium; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D015384:Zona Glomerulosa / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D006150:Guanine Nucleotides; D017483:Receptors, Vasopressin; D010566:Virulence Factors, Bordetella; D014316:Tritium; D001127:Arginine Vasopressin; D009568:Nitrendipine; D037342:Pertussis Toxin; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D011188:Potassium; D002118:Calcium