Distribution of muscarinic acetylcholine receptors in amphibian cardiac muscle

ABSTRACT THE skeletal muscle-nerve junction and many interneuronal synapses are highly specialised and morphologically characterised by a direct apposition of pre- and postsynaptic elements

separated by a cleft of no more than 50 nm, localised thickenings of the apposed membranes and an aggregation of small vesicles in the presynaptic process. At several such ‘focal’ synapses,

neurotransmitter receptor molecules are restricted to patches of postsynaptic membrane corresponding to synaptic sites1–3. For example, at the motor endplate of skeletal muscle,

acetylcholine receptor packing density in the subsynaptic membrane is about 103 times higher than in the extrasynaptic membrane several μm away4–6. Many neuroeffector junctions such as those

in autonomically innervated tissues, however, are much less specialised and lack synaptic membrane apposition and thickenings7,8. In the heart for example, the terminal postganglionic

autonomie axons consist of long chains of vesicle-packed varicosities and form a widely ramifying plexus over the muscle9. The varicosities sometimes lie in close apposition to the muscle

but may often be several μm away from the nearest target. Even when pre- and postsynaptic membranes are closely apposed, morphological specialisation of the membranes is not normally

seen7,10–12. I was interested to determine whether receptor molecules for acetylcholine (ACh) in heart muscle are localised to the relatively infrequent sites of close apposition between

nerve and muscle or are more generally distributed. This report demonstrates that muscarinic ACh receptors are uniformly distributed in cardiac muscle fibres in amphibian heart. Access

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Medicine, Atlanta, Georgia, 30322 H. CRISS HARTZELL Authors * H. CRISS HARTZELL View author publications You can also search for this author inPubMed Google Scholar RIGHTS AND PERMISSIONS

Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE HARTZELL, H. Distribution of muscarinic acetylcholine receptors in amphibian cardiac muscle. _Nature_ 278, 569–571 (1979).

https://doi.org/10.1038/278569a0 Download citation * Received: 14 December 1978 * Accepted: 15 February 1979 * Published: 01 April 1979 * Issue Date: 05 April 1979 * DOI:

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