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Calcium and calcium-activated currents in vagotomized rat primary vagal afferent neurons

Eric Lancaster *, Eun Joo Oh †, Tony Gover * and Daniel Weinreich *†

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 E_Cl, indicating that they were due to Ca²⁺-activated chloride current (I_Cl(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 I_Cl(Ca). These NGNs respond electrically to increases in [Ca²⁺]_i during regeneration.

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