Synaptic transmission in rat cardiac neurones.
Intracellular recordings of spontaneous synaptic activity and synaptic responses to fibre tract stimulation were taken from neurones of ganglia isolated from the left atrium and interatrial septum of the rat. In six out of 57 neurones studied, spontaneous fast excitatory postsynaptic potentials (EPSPs) were recorded. Single stimulation of fibre tracts approaching the ganglion resulted in an all-or-none response consisting of an EPSP, from which an action potential abruptly appeared. This response disappeared in Ca(2+)-free/high-Mg2+ solution, indicating that it was orthodromic in origin. EPSPs were markedly exaggerated and prolonged by neostigmine (1-5 microM). EPSPs produced by high-frequency (0.1-20 Hz) fibre tract stimulation were markedly attenuated when compared with responses to single fibre tract stimulation, although they usually remained suprathreshold for spike initiation. High concentrations of hexamethonium (1 mM) and d-tubocurarine (300 microM) failed to inhibit responses to single fibre tract stimulation, although they completely abolished responses to high-frequency stimulation. Responses to single fibre tract stimulation were abolished by trimetaphan (greater than or equal to 100 microM). No slow synaptic responses were detected during single or high-frequency fibre tract stimulation. All cardiac neurones that responded orthodromically were highly excitable: they had a short post-spike after-hyperpolarization (AHP) and responded with multiple firing to prolonged membrane depolarization. It is concluded that cardiac neurones, in the region of the heart studied here, receive single 'strong' cholinergic inputs from some fibre tracts approaching the ganglion that elicit EPSPs accompanied by spikes. EPSPs are rather resistant to ganglion-blocking agents and subject to frequency modulation.
Selyanko
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Department of Autonomic Nervous System Physiology, A.A. Bogomoletz Institute of Physiology, Kiev, Ukraine.
Skok
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D000200:Action Potentials; D000818:Animals; D002118:Calcium; D005260:Female; D005724:Ganglia / Q000502:physiology; D006325:Heart Atria / Q000294:innervation*; D006346:Heart Septum / Q000294:innervation*; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D008274:Magnesium; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013569:Synapses / Q000502:physiology*; D014294:Trimethaphan / Q000494:pharmacology; D014403:Tubocurarine / Q000494:pharmacology
D006584:Hexamethonium Compounds; D018738:Hexamethonium; D014294:Trimethaphan; D008274:Magnesium; D002118:Calcium; D014403:Tubocurarine