10. ELECTRIC ORGANS
449
are generally much larger than those of ordinary nerve and muscle cells.
The values of membrane resistance in electrocytes are far below
the values for muscle [about 3000 fi cm2 for frog twitch muscle (Eisenberg and Gage, 1969)l. Correspondingly, the current outputs are much
greater. In eel electrocytes the resting resistance of the innervated face
is about 25 0 cm2 according to Nakamura et al. (1965); a value of
19 fi cm2 is reported by Cohen et al. (1969) using a different and
perhaps more accurate technique. The resistance of the uninnervated
face is about 0.2 fi cm2 (Keynes and Martins-Ferreira, 1953). During
activity the resistance of the innervated face decreases to about 1 0 cm2
(calculated from Nakamura et al., 1965), and the peak inward current
is about 60 mA/cm2. These values approach the resistance of the extracellular fluid and cytoplasm in series with the innervated face. Because
of leakage and eddy currents, decrease of the membrane resistances
to much below the series resistance would make the cells less efficient.
In Torpedo the resting resistance across an entire cell is 5-30 fi cm2
( Albe-Fessard, 1950b; Bennett et al., 1961). The peak current during
activity is about 75 mA/cm2 and if the driving force for each cell is
about 90 mV, the series resistance during activity is about 1.2 fi cm2
per cell.
Although the resting and active resistances of the electrocytes are
far below those of muscle membranes, the values are comparable to
those of the node of Ranvier [resting resistance, 30 0 cm2; active
resistance, 2 0 cm2; peak inward current 10 mA/cm2 (Dodge and
Frankenhaeuser, 1959; Frankenhaeuser and Huxley, 1964) 1. Furthermore, the figures for electrocytes are calculated from macroscopic areas
disregarding the considerable surface convolutions, and a more realistic
comparison would be referred to actual areas of plasma membrane. On
the reasonable assumption that the plasma membranes of the electrocytes have a capacity of 1 pF/cm2, one may estimate the true membrane
area from the capacities measured per macroscopic area, which in the
eel is about 15 pF/cm2 (Cohen et al., 1969) and in Torpedo is about
5 pF/cm2 ( Albe-Fessard, 1950b). Thus, the actual membrane parameters probably differ by factors of 5-15 from the reported ones (factors
which appear consistent with the increase in surface seen morphologically, references below), Weakly electric organs tend to have somewhat higher membrane resistances, several tens to several hundred Q
cm2 referred to macroscopic surface. Insufficient data are available for
an accurate comparison among weakly electric organs in terms of area
of plasma membrane, but the membranes-with the exception of membranes acting as a series capacity-all have a shorter time constant than
muscle and presumably are of lower resistivity.
The response characteristic in which electrocytes are most out-
449
are generally much larger than those of ordinary nerve and muscle cells.
The values of membrane resistance in electrocytes are far below
the values for muscle [about 3000 fi cm2 for frog twitch muscle (Eisenberg and Gage, 1969)l. Correspondingly, the current outputs are much
greater. In eel electrocytes the resting resistance of the innervated face
is about 25 0 cm2 according to Nakamura et al. (1965); a value of
19 fi cm2 is reported by Cohen et al. (1969) using a different and
perhaps more accurate technique. The resistance of the uninnervated
face is about 0.2 fi cm2 (Keynes and Martins-Ferreira, 1953). During
activity the resistance of the innervated face decreases to about 1 0 cm2
(calculated from Nakamura et al., 1965), and the peak inward current
is about 60 mA/cm2. These values approach the resistance of the extracellular fluid and cytoplasm in series with the innervated face. Because
of leakage and eddy currents, decrease of the membrane resistances
to much below the series resistance would make the cells less efficient.
In Torpedo the resting resistance across an entire cell is 5-30 fi cm2
( Albe-Fessard, 1950b; Bennett et al., 1961). The peak current during
activity is about 75 mA/cm2 and if the driving force for each cell is
about 90 mV, the series resistance during activity is about 1.2 fi cm2
per cell.
Although the resting and active resistances of the electrocytes are
far below those of muscle membranes, the values are comparable to
those of the node of Ranvier [resting resistance, 30 0 cm2; active
resistance, 2 0 cm2; peak inward current 10 mA/cm2 (Dodge and
Frankenhaeuser, 1959; Frankenhaeuser and Huxley, 1964) 1. Furthermore, the figures for electrocytes are calculated from macroscopic areas
disregarding the considerable surface convolutions, and a more realistic
comparison would be referred to actual areas of plasma membrane. On
the reasonable assumption that the plasma membranes of the electrocytes have a capacity of 1 pF/cm2, one may estimate the true membrane
area from the capacities measured per macroscopic area, which in the
eel is about 15 pF/cm2 (Cohen et al., 1969) and in Torpedo is about
5 pF/cm2 ( Albe-Fessard, 1950b). Thus, the actual membrane parameters probably differ by factors of 5-15 from the reported ones (factors
which appear consistent with the increase in surface seen morphologically, references below), Weakly electric organs tend to have somewhat higher membrane resistances, several tens to several hundred Q
cm2 referred to macroscopic surface. Insufficient data are available for
an accurate comparison among weakly electric organs in terms of area
of plasma membrane, but the membranes-with the exception of membranes acting as a series capacity-all have a shorter time constant than
muscle and presumably are of lower resistivity.
The response characteristic in which electrocytes are most out-