No retinal phenotypes are seen in pumbem mutant flies.
In pumbem aCC/RP2 neurons, the magnitude of the persistent component of voltage-gated Na+ current is significantly increased relative to controls, while the transient component is significantly different. Endogenous membrane excitability in pumbem aCC/RP2 neurons, determined by injection of constant current, is increased relative to controls.
pumbem/pum7 and pumbem/pum9 transheterozygotes exhibit a significantly faster long term facilitation (LTF) at the neuromuscular junction than seen in wild-type. Larvae also respond to nerve stimuli with excitatory junctional potentials (ejp's) about 95% of time (as compared to about 80% in controls) in low Ca2+ (0.15mM) conditions. At 0.10mM Ca2+ an ejp response is seen about 85% of the time (as compared to about 35% in controls).
Flies exhibit greatly reduced coordination, flight ability and fertility. Mutation affects synaptic transmission at the larval neuromuscular junction via an affect on excitability in the motor neuron: the mutation acts presynaptically to cause increased transmitter release. Larvae exhibit a more rapid onset of augmentation than pum+ larvae.