Elsevier

Neuroscience Letters

Volume 561, 21 February 2014, Pages 171-175
Neuroscience Letters

The interaction between tropomyosin-related kinase B receptors and serine kinases modulates acetylcholine release in adult neuromuscular junctions

https://doi.org/10.1016/j.neulet.2013.12.073Get rights and content

Highlights

  • Serine kinases and trkB receptor cooperate in neurotransmitter release.

  • PKC can potentiate ACh release without the involvement of the trkB.

  • trkB needs an operative PKC pathway if it is to potentiate ACh release.

  • To actively stimulate PKA the operativity of trkB is a necessary condition.

  • A consequence of trkB activity can be PKA stimulation.

Abstract

We conducted an electrophysiological study of the functional link between the tropomyosin-related kinase B (trkB) receptor signaling mechanism and serine-threonine kinases, both protein kinase C (PKC) and protein kinase A (PKA). We describe their coordinated role in transmitter release at the neuromuscular junction (NMJ) of the Levator auris longus muscle of the adult mouse. The trkB receptor normally seems to be coupled to stimulate ACh release because inhibiting the trkB receptor with K-252a results in a significant reduction in the size of EPPs. We found that the intracellular PKC pathway can operate as in basal conditions (to potentiate ACh release) without the involvement of the trkB receptor function, although the trkB pathway needs an operative PKC pathway if it is to couple to the release mechanism and potentiate it. To actively stimulate PKA (which also results in ACh release potentiation), the operativity of trkB is a necessary condition, and one effect of trkB may be PKA stimulation.

Introduction

Several signaling mediators and their receptors transmit information between the cells that make up the synapses (pre- and postsynaptic cells and glia). In the neuromuscular synapses on the skeletal muscles, several subtypes of presynaptic muscarinic acetylcholine autoreceptors (mAChRs) [4], [16], [24], [25], adenosine receptors [26] and neurotrophin receptors [2], [17], [18], among others, cooperate to control the functional conditions of transmitter release in response to variable activity demands. These metabotropic receptors are coupled to a limited repertoire of presynaptic effector kinases which finally phosphorylate proteins and regulate neurotransmitter release.

In previous studies, we found that the muscarinic mechanism strongly influences serine-threonine kinase activity, both protein kinase C (PKC) and protein kinase A (PKA) [20], [23]. M1 and M2 subtypes of muscarinic receptors were involved in enhancing and inhibiting ACh release, respectively. Also, PKA (but not PKC) plays a constitutive role in promoting a component of normal release. The selective block of M1 or M2 inverts this kinase function: PKC can then stimulate transmitter release, whereas PKA is uncoupled [21]. Here, we use electrophysiological techniques to investigate the functional interactions between the neurotrophin receptor tropomyosin-related kinase B (trkB) receptor, which binds the target-derived brain-derived neurotrophic factor (BDNF) and neurotrophin-4 (NT-4) [8], and the serine-threonine kinases PKC and PKA and to demonstrate their coordinated role in transmitter release.

It is generally believed that neurotrophin receptors promote local acute effects in nerve endings, and retrograde long-term effects in distant neuronal cell bodies [6], [7], [9], [11], [13], [14]. Here we analyzed the acute effect on transmitter release resulting from changes in trkB and serine kinases.

Section snippets

Animals

Experiments were performed on the Levator auris longus (LAL) muscle of adult male Swiss mice (30–40 days postnatal; Criffa, Barcelona, Spain). The animals were anesthetized with 2% tribromoethanol (0.15 ml/10 g body weight, I.P.) and killed by exanguination while deeply anesthetized. The total number of mice studied was 95. The animals were cared for in accordance with the guidelines of the European Community's Council Directive of 24 November 1986 (86/609/EEC) for the humane treatment of

Results and discussion

In a previous study [8], we found that exogenously added BDNF (10 nM) potentiates evoked ACh release in a trkB and p75NTR receptor dependent manner because potentiation is prevented by the pharmacological block of trkB (K-252a, 200 nM, 1 h) or p75NTR (Pep5, 1 μM, 1 h). The inhibition of the trkB receptor with K-252a does not merely prevent the effect of exogenous BDNF, but also gives rise by itself to a significant reduction in the size of EPPs (∼50%) after one hour of incubation (Fig. 1, Fig. 2,

Acknowledgements

This work was supported by a grant from MEC (SAF2011-23711) and a grant from the Catalan Government (Generalitat) (2009SGR01248).

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    These authors contributed equally to this work.

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