G-proteins coupled to phosphoinositide hydrolysis in the cochlear and vestibular sensory epithelia of the rat are insensitive to cholera and pertussis toxins.
In the cochlear (CSE) and vestibular sensory epithelia (VSE), phosphoinositides are hydrolyzed in response to stimulation of phospholipase C (PLC) by cholinergic muscarinic and purinergic P2y agonists. Such receptor-mediated activation of PLC is expected to be coupled through guanine nucleotide-binding proteins (G-proteins). Although several classes of G-proteins have been identified in the inner ear, nothing is known about the type of G-proteins associated with the phosphoinositide second messenger system in CSE and VSE. Phosphoinositide hydrolysis was determined by the release of radiolabeled inositol phosphates (InsPs). Ten mM NaF plus 10 microM AlCl3 increased basal InsPs accumulation 2-fold in both CSE and VSE of the rat. Release of InsPs was also enhanced by guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S) in saponin-permeabilized tissues. Furthermore, release of InsPs stimulated by both carbamylcholine (CCh) and adenosine 5'-O-[3-thiotriphosphate] (ATP-gamma-S) was significantly inhibited by 100 microM guanosine 5'-O-[2-thiodiphosphate] (GDP-beta-S). These results strongly suggest the involvement of G-proteins in the receptor-PLC coupling in CSE and VSE. ADP-ribosylation in membrane fractions of CSE and VSE in the presence of cholera toxin (CTX) or pertussis toxin (PTX) indicated the existence of Gs- and G(i)-type G-proteins. However, neither CTX nor PTX affected basal or agonist-stimulated release of InsPs. These observations suggest that muscarinic and P2y purinergic receptors are coupled to PLC via CTX- and PTX-insensitive G-proteins in CSE and VSE.
Kresge Hearing Research Institute, University of Michigan, Ann Arbor 48109-0506.
K
K
Ogawa
J
J
Schacht
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000077410:Aluminum Chloride; D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D002712:Chlorides / Q000494:pharmacology; D002772:Cholera Toxin / Q000633:toxicity; D003051:Cochlea / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D004351:Drug Resistance; D004848:Epithelium / Q000187:drug effects / Q000294:innervation / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006868:Hydrolysis; D008297:Male; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D012969:Sodium Fluoride / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D014722:Vestibule, Labyrinth / Q000187:drug effects / Q000294:innervation / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000633:toxicity
D017607:Aluminum Compounds; D002712:Chlorides; D010716:Phosphatidylinositols; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; D000246:Adenosine Diphosphate Ribose; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000077410:Aluminum Chloride; C023427:guanosine 5'-O-(2-thiodiphosphate); D012969:Sodium Fluoride; D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins