American Zoologist 1966 6(2):107-122; doi:10.1093/icb/6.2.107
© 1966 by The Society for Integrative and Comparative Biology
The Sites of Action of Pericardial Organ Extract and 5-Hydroxytryptamine in the Decapod Crustacean Heart
Responses of isolated, perfused hearts of
Homarm americanus to brief, internal application of extracts of pericardial organs
(PO's) of
Cancer borealis, or 5-hydroxytryptamine (5HT) are very
similar over a thousand-told range of concentration: an increase
in rate and amplitude of beating. These reach their maxima after
washing out has begun, and recover within ten minutes. External
application is ineffective and the substances do not interact
with effects of stretch stimulation. Intracellular recording
from heart muscle fibers reveals facilitation of depolarization
to bursts at heart beat frequencies. There may be some effect
of 5HT directly on neuromuscular facilitation. Responses recorded
from isolated cardiac ganglia show increased burst rate, burst
duration, or both. Thresholds and the range of concentrations
for which coordinated responses are recorded correspond to those
for perfused hearts. It is concluded that the major sites of
action of PO extract and 5HT are in the cardiac ganglion. 5HT
tachyphlaxis and LSD block effects of 5HT, but not of PO extract
or accelerator nerve stimulation. Intracellular recordings from
the large ganglion cells show no effects on resting, synaptic,
or spike potentials. Changes in membrane potential to current
pulses revealed no changes in membrane resistance or in the
resistance of the electrotonic pathway between cells. Results
of selective application to large or small cells suggested that
PO extract may contain a rate-increasing substance and one prolonging
the duration of bursts. The former, and 5HT, may influence pacemaker
potentials; the latter may increase the number of spikes a unit
can produce before becoming refractory.
CiteULike 
Connotea 
Del.icio.us What's this?
