The inhibitory neuromuscular junction of C. elegans is a relatively simple GABA synapse that is a useful model to study how GABA receptors are patterned in developing and adult animals. A single postsynaptic GABA receptor, UNC-49, functions at this synapse. UNC-49 exhibits homeostatic plasticity: when worms are exposed to the GABA agonist muscimol, UNC-49 levels are reduced up to 10-fold over the course of 10 hours. Worms exposed to muscimol initially display flaccid paralysis, possibly due to chronic muscle hyperpolarization caused by GABA receptor activation. To further explore the relationship between membrane hyperpolarization and GABA receptor downregulation, we measured GABA receptor levels in
twk-18(
cn110) mutants. TWK-18 is a twin-pore domain potassium channel expressed in body wall muscles that exhibits steep temperature dependence of activity.
cn110 is a dominant allele that shows abnormally large currents. At 20degC,
twk-18(
cn110) mutants behave normally, but at 30degC, they exhibit rapid-onset, reversible, flaccid paralysis due to muscle hyperpolarization, thus phenocopying the acute effects of muscimol exposure. Using quantitative immunofluorescence, we examined GABA receptor levels in wild-type and
twk-18(
cn110) adults that had been raised at 20degC, and shifted to 30degC for various times. UNC-49 levels were reduced three- to five-fold in
twk-18(
cn110) mutants compared to wild-type, but surprisingly, this reduction occurred in all of the mutants, including the controls that were maintained at 20degC. Patch-clamp recordings demonstrated similarly reduced GABA currents. Levamisole treatment, which chronically depolarizes muscles, did not reverse the effects of the
twk-18(
cn110) mutation. These results suggested that hyperpolarization can influence GABA receptor abundance, but that the effect may be developmental. We are now examining the developmental time-course of GABA receptor abundance at synapses. At 20degC wild-type and
twk-18(
cn110) synapses showed equivalent GABA receptor abundance through the early adult stage. Within the next 48 hours, wild-type synapses showed a 2-3 fold increase in GABA receptor levels while
twk-18(
cn110) synapses stayed the same. Interestingly, this induction of GABA receptor expression did not occur at 15degC in either wild-type or
twk-18(
cn110) mutants. Together, these results suggest that GABA receptor levels may be set in response to both membrane potential and temperature during a transient developmental window.