G-proteins coupled to phosphoinositide hydrolysis in the cochlear and vestibular sensory epithelia of the rat are insensitive to cholera and pertussis toxins

Kaoru Ogawa, Jochen Schacht

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)

Abstract

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 μM 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-γ-S) in saponin-permeabilized tissues. Furthermore, release of InsPs stimulated by both carbamylcholine (CCh) and adenosine 5'-O-[3-thiotriphosphate](ATP-γ-S) was significantly inhibited by 100 μM guanosine 5'-O-[2-thiodiphosphate](GDP-β-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 Gi-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.

Original languageEnglish
Pages (from-to)197-203
Number of pages7
JournalHearing Research
Volume74
Issue number1-2
DOIs
Publication statusPublished - 1994 Apr
Externally publishedYes

Keywords

  • ADP-ribosylation
  • Cholera toxin
  • Cochlea
  • G-protein
  • Inositol phosphate
  • Pertussis toxin
  • Rat
  • Vestibule

ASJC Scopus subject areas

  • Sensory Systems

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