Evidence against a role for a pertussis toxin-sensitive G protein in Ca2+ mobilization in rat parotid acinar cells.
Hormone-induced Ca2+ mobilization in rat parotid acinar cells is reportedly mediated via an as yet uncharacterized G protein. We have studied the sensitivity to pertussis toxin (PTx) of this signal transduction mechanism. When rats were treated with Ptx (1.3-1.5 micrograms per animal) for 72 h, a 41 kDa membrane protein was ADP-ribosylated. This PTx treatment regimen, also, resulted in a more than 80% block of the ability of the muscarinic agonist carbachol to inhibit beta-adrenergic receptor-stimulated parotid adenylyl cyclase activity. However, cytosolic Ca2+ levels, in response to either carbachol or AIF-4, were comparable in cells prepared from both untreated or PTx-treated rats, when incubated either in the absence or presence of extracellular Ca2+. Further, both the sensitivity of the Ca2+ response to carbachol and the ability of the agonist-sensitive intracellular Ca2+ stores to be refilled by extracellular Ca2+ were unaffected by PTx treatment. Parotid membranes also contained three low-molecular-weight GTP-binding proteins (25, 22 and 18 kDa) which were unaffected by PTx. These results show that there is only one detectable substrate in parotid membranes for a PTx-catalyzed ADP-ribosylation and that hormone-induced Ca2+ mobilization events in parotid acinar cells are not mediated via PTx-sensitive components.
Ambudkar
I S
IS
Clinical Investigations and Patient Care Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, MD 20892.
Horn
V J
VJ
Dai
Y S
YS
Baum
B J
BJ
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000187:drug effects; D000535:Aluminum / Q000494:pharmacology; D017607:Aluminum Compounds; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D010306:Parotid Gland / Q000378:metabolism*; D037342:Pertussis Toxin; D051381:Rats; D011919:Rats, Inbred Strains; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D017607:Aluminum Compounds; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D002217:Carbachol; D000535:Aluminum; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D005459:Fluorides; D002118:Calcium; C032311:aluminum fluoride