RESEARCH

pH Dependence of Neural Function

As biochemical processes are pH-sensitive, the nervous system has evolved to either ameliorate or accommodate pH changes generated by its own activity.  The mechanisms that do this are rarely examined as pH changes occurring in an experimental context are routinely suppressed using high concentrations of zwitterionic pH buffers, hampering efforts to elucidate mechanisms underpinning neurological symptoms accompanying acid/base disorders. Our efforts to elucidate pH-sensitive elements of a gain mechanism sustaining glutamatergic neurotransmission provide a pH-centric perspective on short-term synaptic plasticity and potentially critical insight into certain neurological conditions.

We are pursuing the following projects, and welcome the participation of graduate students:

Uncovering a Synaptic Gain Mechanism.

We have uncovered a gain mechanism at the Drosophila neuromuscular junction (NMJ) that relies on activity-dependent alkalinization in the synaptic cleft. We hypothesize that the “gain” is dependent on alkalization at the extracellular face of either Acid Sensing Ion Channels (ASICs) or Voltage-Gated Ca²+ Channels (VGCCs).  To further elucidate this gain mechanism, we have designed highly specific membrane-tethered inhibitors to block ASICs, VGCCs and various ion-transporters. The same inhibitors will allow for testing of the gain mechanism’s involvement in learning and memory, and NMJ function.

pH Sensitivity of ASIC and VGCC Splice Isoforms.

The magnitude of the gain mechanism’s effect is different between terminals of different motor neurons, raising the question of whether different ASIC and VGCC splice isoforms manifest different degrees of pH sensitivity. To test for an association of specific isoforms with different degrees of pH sensitivity, we designed novel bichromatic “exon reporters”.  These reporters allow us to detect differences in exon usage in individual neurons in vivo, allowing us to identify those ASICs and VGCCs motifs that confer pH sensitivity.

A Screen for Genes Essential for Neural Acid/Base Homeostasis.

Even mild systemic acid/base imbalance is accompanied by a suite of neurological symptoms ranging from headache and lethargy (acidosis) to confusion and dizziness (alkalosis). Using pH sensors developed in our laboratory, we are screening for the genes most critical for maintaining acid/base homeostasis in the central nervous system in the face of challenges to acid/base balance.

Molecular Evolution of pH Sensors.

The pH-sensitive GFP variants identified by Gero Meisenbock in 1998 still have the greatest dynamic range of any genetically-encoded pH sensor. We are seeking collaboration with a microbiologist to evolve new fluorescent protein variants with pH-sensitive characteristics superior to super-ecliptic pHluorin and to test their utility in neurons, glia and the interstitium of the nervous system.