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Fig. 6. Intracellular recordings from subumbrellar muscle cells approximately
2–2.5 mm from the nerve ring. (A) A double recording from a radial
muscle cell (top trace) and a circular muscle cell (bottom trace). An initial
spontaneous swim produced a full action potential (with initial junctional
potential) in the circular muscle cell, but only a `field effect' in the
radial cell. When electrical stimuli were delivered to the segment with a
suction electrode, both a junctional potential (circular muscle cell) and an
action potential (radial muscle cell) were triggered. The small `blip' before
each event is the stimulus artifact. (B) Variability in the shape and
amplitude of circular muscle action potentials. Each event is initiated by a
single junctional potential. All were spontaneously generated in a reduced
preparation that showed varying contractions. This recording was from a small
medusa, 3 cm bell diameter, so the action potentials are of a shorter
duration. (C) Complex electrical event from a circular muscle cell in a
segment in which a radial response was triggered by a mechanical stimulus
(light touch with a glass micropipette electrode) delivered to the velum in
the region of that segment. The contraction in that segment was weaker than in
the adjacent segments on each side.
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