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Received August 8, 2001
Accepted after revision January 29, 2002
1 The Neuroscience Program, University of Maryland, School of Medicine, 655 W. Baltimore Street, Baltimore, MD 21201-1559, USA
2 Department of Pharmacology and Experimental Therapeutics, University of Maryland, School of Medicine, 655 W. Baltimore Street, Baltimore, MD 21201-1559, USA
3 Department of Pharmacology and Experimental Therapeutics, University of Maryland, School of Medicine, Bressler Research Building, Room 4-002, 655 West Baltimore Street, Baltimore, MD 21201-1559, USA
* To whom correspondence should be addressed. E-mail: dweinrei{at}umaryland.edu.
Adult inferior vagal ganglion neurons (nodose ganglion neurons, NGNs) were acutely isolated 4-6 days after section of their peripheral axons (vagotomy) and examined with the whole-cell patch-clamp technique. A subset (~25 %) of vagotomized NGNs displayed depolarizing after-potentials (DAPs), not present in control NGNs. DAPs were inhibited by niflumic acid (125 µm) or cadmium (100 µm), and had a reversal potential near ECl, indicating that they were due to Ca2+-activated chloride current (ICl(Ca)). N-type, L-type, T-/R- and other types of voltage-dependent Ca2+ channels provided about 43, 2, 16 and 40 % of the trigger Ca2+ for DAP generation, respectively. Intracellular Ca2+ concentration ([Ca2+]i) was estimated using fura-2 fluorescence. Resting [Ca2+]i and peak [Ca2+]i elevation induced by activating Ca2+-induced Ca2+ release (CICR) stores with 10 mm caffeine were not significantly different among control NGNs, vagotomized NGNs with DAPs and vagotomized NGNs without DAPs, averaging 54 ± 7.9 (n = 19; P = 0.49) and 2022 ± 1059 nm (n = 19; P = 0.44), respectively. Blocking CICR with 10 µm ryanodine reduced DAP amplitude by ~37 %. Ca2+ influx induced by action potential waveforms was increased by over 250 % in vagotomized NGNs with DAPs (19.0 ± 2.1 pC) compared to control NGNs (5.0 ± 0.8 pC) or vagotomized NGNs without DAPs (7.0 ± 0.8 pC). L-type, N-type, T-/R-type and other types of Ca2+ influx were increased proportionately in vagotomized NGNs with DAPs. In conclusion, a subset of vagotomized NGNs have increased Ca2+ currents and express ICl(Ca). These NGNs respond electrically to increases in [Ca2+]i during regeneration.
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