ISSN:
1432-1351
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary 1. The activation of cardiac muscle fibres by the motor axons from the cardiac ganglion of the crab,Portunus sanguinolentus, is described here (Fig. 1). 2. Each cardiac muscle fibre receives polyneuronal innervation, and the synaptic potentials recorded in the fibres of spontaneously active hearts are in part compound excitatory junctional potentials (EJP's) resulting from simultaneous synaptic input from several axons terminating close to one another on the muscle fibre (Fig. 2). 3. In situ recording from spontaneously beating whole hearts shows that the compound EJP's normally summate to form an irregular, depolarised plateau potential (Fig. 3). 4. Portunus cardiac muscle fibres show a regenerative response to synaptic excitation in addition to the summated, compound EJP's. In freshly exposed, whole hearts, this response takes the form of an overshooting action potential much shorter in duration than an EJP. More than one action potential can occur in response to a single burst of input from the spontaneously active cardiac ganglion (Fig. 3). 5. These observations suggest that the normal electrical activity in the cardiac muscle fibres of the living animal consists of an overshooting action potential rising from resting potential and followed by a slowly declining, irregular plateau of summated, compound EJP's (Fig. 3). 6. Bath- and iontophoretically-applied glutamate (10−4 M) transiently depolarises the cardiac muscle fibres and abolishes their response to synaptic input (Fig. 4). 7. In response to intracellular current injection via a microelectrode, the fibre membrane I-V relation is linear in the depolarising direction at least as far as 18mV(Fig. 5). 8. Replacement of the Ca2+ ions in the bathing medium with Sr2+ ions results in spontaneous, rhythmic, long-duration action potentials in the muscle fibres of deganglionated hearts (Fig. 6).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00611172
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