Fig. 4. Intracellular recordings reveal altered depolarization in action potentials
from cca-1 mutant pharynxes. (A) Sample intracellular voltage
recordings from wild-type and cca-1(ad1650) mutant worms. While the
depolarization phase of the wild-type action potential usually rises steeply
and steadily from resting potential to a peak, action potentials from
cca-1 mutant worms often display a notch or flattened area early in
depolarization. (B) Average maximal rising phase slopes for the wild-type,
cca-1, eat-2 and eat-2; cca-1. 50-100
differentiated and aligned action potentials were averaged for each individual
pharynx. A peak slope for each individual pharynx was obtained from the
averaged trace. This calculation was performed for 19 wild-type animals, 16
cca-1 mutant animals, 14 eat-2 mutant animals and 11
eat-2; cca-1 double mutant animals. From the peak slopes for each
individual, an average peak slope was calculated for each genotype, expressed
as mean ± S.E.M.
*Significantly different from the wild type;
significantly different from all other strains
(P<0.005 for all comparisons, t-test). (C) (Top)
Superimposed action potentials (with rising phases aligned) from two
representative wild-type pharynxes. (Bottom) Time derivatives of the action
potentials above. N=63 and 66 for left and right traces,
respectively. (D) Same as in C for two representative cca-1(ad1650)
worms; N=51 and 74 for left and right panels, respectively. While
wild-type action potentials generally display a smooth steep rising phase, the
majority of action potentials from cca-1 mutant worms contain an
initial depolarization, followed by a flattened area or notch. Plotting the
time derivative of each action potential trace reproduces the EPG phenotypes
of wild-type and cca-1 mutant worms (compare with
Fig. 3) with a small, delayed
depolarization spike following each initial rise in membrane potential. (E)
Action potentials from two representative eat-2(ad465); cca-1(ad1650)
double mutants, labeled as in C and D. These action potentials lack the
initial depolarization and plateau seen in cca-1 single mutants,
suggesting that early depolarization in a wild-type pharynx or cca-1
mutant pharynx is mediated by the EAT-2-containing nicotinic receptor.