Involvement of a GTP-binding protein in stimulating action of angiotensin II on calcium channels in vascular smooth muscle cells.
The possible involvement of a GTP-binding protein in the regulation of Ca2+ channels by angiotensin II (Ang II) in vascular muscle cells was investigated by the whole-cell voltage-clamp method. Single cells were freshly isolated from guinea pig portal vein. The pipette solution contained high Cs+ to inhibit K+ currents and thereby isolate the Ca2+ channel current. Ba2+ (2 mM) was in the bath solution as a charge carrier for the Ca2+ channel. Application of Ang II (0.1-100 nM) produced an increase in peak amplitude of the Ba2+ current, with a shift of the current-voltage curve in the negative direction. These effects were inhibited by pretreatment with an antagonist of the Ang II receptor, [Sar1,Ile8]-Ang II. Presence of 0.1 mM GTP in the pipette solution stabilized the Ang II action, but 0.3-1.0 mM GDP-beta-S and 1.0 mM GTP-gamma-S inhibited it. GTP-gamma-S alone produced a slowly progressing increase in the basal (unstimulated) current amplitude. Preincubation of muscle tissues with pertussis toxin (1 micrograms/ml, for up to 6 hours at 36 degrees C) or intracellular application of preactivated pertussis toxin (1 micrograms/ml) plus NAD (1 mM) did not inhibit the Ang II action. Cholera toxin (10 micrograms/ml) also had no effect on the Ang II action. These results suggest that the Ang II stimulation of Ca2+ channels in smooth muscle of guinea pig portal vein may be mediated by a G protein that is insensitive to both pertussis toxin and cholera toxin.
Ohya
Y
Y
Department of Physiology and Biophysics, University of Cincinnati, Ohio 45267-0576.
Sperelakis
N
N
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001464:Barium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D002772:Cholera Toxin / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000031:analogs & derivatives / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D037342:Pertussis Toxin; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015220:Calcium Channels; D010566:Virulence Factors, Bordetella; C034883:guanosine 5'-O-(2-thiotriphosphate); D000804:Angiotensin II; D001464:Barium; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins