Activity-dependent intracellular Ca2+ transients in unmyelinated nerve fibres of the isolated adult rat vagus nerve |
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Authors: | J Wächtler C Mayer Peter Grafe |
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Institution: | Physiologisches Institut, Ludwig-Maximilians-Universit?t München, Pettenkoferstrasse 12, D-80336 Munich, Germany, DE
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Abstract: | Confocal laser scanning microscopy was used to follow changes in the free intracellular calcium concentration (Ca2+]i) in nerve fibres and adjacent Schwann cells in isolated rat vagus nerves. Ca2+]i was monitored by the Ca2+-sensitive fluorescent dyes Calcium Green-1 and Fura Red. Intracellular Ca2+ transients were observed during repetitive (1–50 Hz) supramaximal electrical stimulation or by bath application of ATP. Trains
of action potentials were more effective at elongated, fibre-like structures of the vagus nerves, whereas ATP-induced Ca2+ transients were found predominantly in regions of Schwann cell bodies. Activity-induced Ca2+ signals were unaffected by pharmacological manipulation of intracellular Ca2+ stores, during long-lasting application of purinergic receptor agonists, or by substitution of extracellular Na+ with Li+. However, they were abolished in the presence of Ca2+-free bathing solution or after the blocking of Ca2+ channels with Cd2+. Ca2+ transients were also observed during Ca2+ action potentials. Such ”Ca2+ spikes” were elicited by electrical stimulation in the presence of a combination of tetrodotoxin and K+ channel blockers. These data suggest that voltage-dependent Ca2+ channels, activated during short trains of Na+ action potentials, produce an increase in intra-axonal Ca2+] of rat vagus nerves. We did not find evidence for activity-dependent Ca2+ transients in the Schwann cells surrounding the unmyelinated axons.
Received: 16 September 1997 / Received after revision: 25 November 1997 / Accepted: 27 November 1997 |
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Keywords: | C fibre Fluorescence Confocal microscopy Fura Red Calcium Green Capsaicin ATP Schwann cell |
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