10. ELECTRIC ORGANS
355
hummers from the sound one perceives when the electric pulses are fed
into a loudspeaker system. Variable frequency species include the mormyrids and many gymnotids. Constant frequency species include the
remainder of the gymnotids and Gymnurchus. Gymnarchus, mormyrids,
and several gymnotids are able to cease discharging for brief periods.
This response appears to represent hiding by keeping quiet electrically
and may also function in communication. Discharge patterns of weakly
electric organs in marine fish are intermittent, but are poorly known
under natural conditions.
11. ELECTRIC ORGANS AND ELECTROCYTES
A. Methods
An introduction to methods of establishing the properties of electrocytes may be helpful at this point. Microelectrodes are placed intracellularly and at various sites externally. Potentials at the tips can then
be recorded by suitable amplifiers and associated equipment. A recording
is termed monopolar if it represents the potential difference between the
electrode tip and a distant grounded electrode in the vessel containing
the preparation. The distant electrode is often called the indifferent
electrode because it is sufficiently far from the active cell that moving it
around does not detectably affect the recorded potential. One may use
a differential amplifier to subtract the potential recorded through one
microelectrode from that recorded through another; the result is differential recording. Monopolar recordings can also be subtracted after the
experiment to obtain the same result.
In discussing properties of single electrocytes it is useful to have an
equivalent circuit. As a first approximation one can consider an electrocyte to be a flattened cell with uniform potentials across each face that
differ from each other during activity. Because of the uniformity of
potential, each face can be given a simple equivalent circuit like those
used for other membranes. (Of course a “naked” cell could not have a
discontinuous change in potential at the edge of the cell for this would
require an infinite current density. However, an electrocyte is often situated in an insulating connective tissue sheath that adheres closely to its
edges, and the potentials over the faces are indeed quite uniform. In any
case the nonuniformities are not important for most considerations of
membrane properties.) Separate branches of the equivalent circuits for
each membrane can be assigned to different ion species, each branch
with a particular internal (equilibrium or Nernst) potential and a con-
355
hummers from the sound one perceives when the electric pulses are fed
into a loudspeaker system. Variable frequency species include the mormyrids and many gymnotids. Constant frequency species include the
remainder of the gymnotids and Gymnurchus. Gymnarchus, mormyrids,
and several gymnotids are able to cease discharging for brief periods.
This response appears to represent hiding by keeping quiet electrically
and may also function in communication. Discharge patterns of weakly
electric organs in marine fish are intermittent, but are poorly known
under natural conditions.
11. ELECTRIC ORGANS AND ELECTROCYTES
A. Methods
An introduction to methods of establishing the properties of electrocytes may be helpful at this point. Microelectrodes are placed intracellularly and at various sites externally. Potentials at the tips can then
be recorded by suitable amplifiers and associated equipment. A recording
is termed monopolar if it represents the potential difference between the
electrode tip and a distant grounded electrode in the vessel containing
the preparation. The distant electrode is often called the indifferent
electrode because it is sufficiently far from the active cell that moving it
around does not detectably affect the recorded potential. One may use
a differential amplifier to subtract the potential recorded through one
microelectrode from that recorded through another; the result is differential recording. Monopolar recordings can also be subtracted after the
experiment to obtain the same result.
In discussing properties of single electrocytes it is useful to have an
equivalent circuit. As a first approximation one can consider an electrocyte to be a flattened cell with uniform potentials across each face that
differ from each other during activity. Because of the uniformity of
potential, each face can be given a simple equivalent circuit like those
used for other membranes. (Of course a “naked” cell could not have a
discontinuous change in potential at the edge of the cell for this would
require an infinite current density. However, an electrocyte is often situated in an insulating connective tissue sheath that adheres closely to its
edges, and the potentials over the faces are indeed quite uniform. In any
case the nonuniformities are not important for most considerations of
membrane properties.) Separate branches of the equivalent circuits for
each membrane can be assigned to different ion species, each branch
with a particular internal (equilibrium or Nernst) potential and a con-