Angiotensin II negatively modulates L-type calcium channels through a pertussis toxin-sensitive G protein in adrenal glomerulosa cells.
In bovine adrenal glomerulosa cells, angiotensin II and extracellular K+ stimulate aldosterone secretion in a calcium-dependent manner. In these cells, physiological concentrations of extracellular potassium activate both T-type (low threshold) and L-type (high threshold) voltage-operated calcium channels. Paradoxically, the cytosolic calcium response to 9 mM K+ is inhibited by angiotensin II. Because K+-induced calcium changes observed in the cytosol are almost exclusively due to L-type channel activity, we therefore studied the mechanisms of L-type channel regulation by angiotensin II. Using the patch-clamp method in its perforated patch configuration, we observed a marked inhibition (by 63%) of L-type barium currents in response to angiotensin II. This effect of the hormone was completely prevented by losartan, a specific antagonist of the AT1 receptor subtype. Moreover, this inhibition was strongly reduced when the cells were previously treated for 1 night with pertussis toxin. An effect of pertussis toxin was also observed on the modulation by angiotensin II of the K+ (9 mM)-induced cytosolic calcium response in fura-2-loaded cells, as well as on the angiotensin II-induced aldosterone secretion, at both low (3 mM) and high (9 mM) K+ concentrations. Finally, the expression of both Go and Gi proteins in bovine glomerulosa cells was detected by immunoblotting. Altogether, these results strongly suggest that in bovine glomerulosa cells, a pertussis toxin-sensitive G protein is involved in the inhibition of L-type channel activity induced by angiotensin II.
Maturana
A D
AD
Division of Endocrinology and Diabetology, Department of Internal Medicine, University Hospital, 24 rue Micheli-du-Crest,CH-1211 Geneva 14, Switzerland.
Casal
A J
AJ
Demaurex
N
N
Vallotton
M B
MB
Capponi
A M
AM
Rossier
M F
MF
D000450:Aldosterone / Q000378:metabolism; D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D002417:Cattle; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000378:metabolism*; D019808:Losartan / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D011188:Potassium / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*; D015384:Zona Glomerulosa
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D010566:Virulence Factors, Bordetella; D000804:Angiotensin II; D000450:Aldosterone; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D019808:Losartan; D011188:Potassium; D002118:Calcium