title: Localized IP3-evoked Ca2+ release activates a K+ current in primary vagal sensory neurons.
abstract: Electrophysiological and microfluorimetric techniques were used to determine whether intracellular photorelease of caged IP(3), and the consequent release of Ca(2+), could trigger a Ca(2+)-activated K(+) current (I(IP3)). Photorelease of caged IP(3) evoked an I(IP3) that averaged 2.36 +/- 0.35 (SE) pA/pF in 24 of 28 rabbit primary vagal sensory neurons (nodose ganglion neurons, NGNs) voltage-clamped at -50 mV. I(IP3) was abolished by intracellular BAPTA (2 mM), a Ca(2+) chelator. Changing the K(+) equilibrium potential by increasing extracellular K(+) ion concentration caused a predicted Nernstian shift in the reversal potential of I(IP3). These results indicated that I(IP3) was a Ca(2+)-dependent K(+) current. I(IP3) was unaffected by three common antagonists of Ca(2+)-activated K(+) currents: bath-applied iberiotoxin (50 nM) or apamin (100 nM), and intracellular 8-Br-cAMP (100 microM) included in the patch pipette. We have previously demonstrated that both IP(3)-evoked Ca(2+) release and Ca(2+)-induced Ca(2+) release (CICR) are co-expressed in NGNs and that CICR can trigger a Ca(2+)-activated K(+) current. In the present study, using caffeine, a CICR agonist, to selectively attenuate intracellular Ca(2+) stores, we showed that IP(3)-evoked Ca(2+) release occurs independently of CICR, but interestingly, that a component of I(IP3) requires CICR. These data suggest that IP(3)-evoked Ca(2+) release activates a K(+) current that is pharmacologically distinct from other Ca(2+)-activated K(+) currents in NGNs. We describe several models that explain our results based on Ca(2+) signaling microdomains in NGNs.
authors.affiliation: Medical Biotechnology Center, Biotechnology Institute and Department of Physiology and Pharmacology, School of Medicine, University of Maryland, Baltimore, Maryland 21201, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Hoesch
authors.forename: Daniel
authors.initials: D
authors.lastname: Weinreich
authors.forename: Joseph P Y
authors.initials: JP
authors.lastname: Kao
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002138:Calibration; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004594:Electrophysiology; D005110:Extracellular Space / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010782:Photolysis; D024681:Potassium Channels, Calcium-Activated / Q000819:agonists*; D011817:Rabbits; D014630:Vagus Nerve / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
chemical_list: D002614:Chelating Agents; D007202:Indicators and Reagents; D024681:Potassium Channels, Calcium-Activated; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium