Photolysis of caged inositol 1,4,5-trisphosphate induces action potentials in frog vomeronasal microvillar receptor neurones.
To study the effect of inositol 1,4,5-trisphosphate (IP(3)) in isolated frog vomeronasal microvillar receptor neurones, whole-cell recordings were performed with 0.5 microM caged IP(3) dissolved in the pipette solution. IP(3) was released by photolysis of caged IP(3) initiated by a 0.8-ms ultraviolet flash from a xenon flash lamp 70 s after the start of dialysis of caged IP(3) into the cell. Flash illuminating the whole receptor neurone with caged IP(3) triggered action potentials when the current was clamped at zero and a series of transient inward currents of 12-55 pA at a holding potential of -70 mV. The average number of spikes during the first 40 s after release of IP(3) was 7.2+/-2.5 (n=6, mean+/-S.E.M.). The average maximum current and the total inward transport of charge during the first 40 s after photolysis of caged IP(3) were -24+/-8.0 pA and -1.7+/-0.8 pC, respectively (n=5, mean+/-S.E.M.). Inward membrane currents of 12-55 pA after release of IP(3) were not observed with 50 microM La(3+) in the bath. Notably, flash focused on the terminal vesicle also triggered action potentials. No action potentials were observed following flash focused on the soma or outside the dendrite. The average number of spikes during the first 40 s after release of IP(3) initiated by flash spatially restricted to the terminal vesicle was 5.0+/-2.0 (n=4, mean+/-S.E.M.).The present study indicates that local release of IP(3) in the terminal vesicle of the vomeronasal neurones triggers transient depolarizations and induces action potentials. We suggest that IP(3) might be a second messenger in the vomeronasal microvillar receptor neurones.
Gjerstad
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National Institute of Occupational Health, Pb 8149 Dep, N-0033, Oslo, Norway. johannes.gjerstad@stami.no
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D000200:Action Potentials / Q000187:drug effects / Q000528:radiation effects; D000818:Animals; D002628:Chemoreceptor Cells / Q000502:physiology*; D003956:Dialysis; D004347:Drug Interactions; D004553:Electric Conductivity; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology*; D007811:Lanthanum / Q000494:pharmacology; D008871:Microvilli / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000528:radiation effects*; D018408:Patch-Clamp Techniques / Q000379:methods; D010782:Photolysis; D011896:Rana temporaria; D013997:Time Factors; D019147:Vomeronasal Organ / Q000166:cytology* / Q000187:drug effects / Q000528:radiation effects
C028521:lanthanum chloride; C061868:inositol 1,4,5-trisphosphate 1-(2-nitrophenyl)ethyl ester; D007811:Lanthanum; D015544:Inositol 1,4,5-Trisphosphate