Department Chair

I. Martha Skerrett, Ph.D.

Date of Award


Access Control

Open Access

Degree Name

Biology, M.A.


Biology Department


Derek Beahm, Ph.D

Department Home page

First Reader

Derek Beahm, Ph.D.

Second Reader

I. Martha Skerrett, Ph.D.

Third Reader

Gregory Wadsworth, Ph.D.


Gap junction channels formed by connexin proteins are critical for the health and function of the vertebrate lens. It is important to understand how these channels are affected by pH because a pH gradient exists in lens tissue. Intracellular pH (pHi) is a regulator of gap junction coupling, and different connexins show different sensitivities to pHi. A “Particle-Receptor” model for pH-dependent channel closure involves the intramolecular interaction between the cytoplasmic tail of the connexin and a region near the mouth of the channel dependent on a highly conserved histidine residue at position 95. While this model explains the pH sensitivity of some connexins, removal of H95 or truncation of the C-tail does not affect the lens connexin, Cx46. The goal of this thesis was to explore the roles of histidines residues located at and near position 95 for the other lens connexin, Cx50. Site-directed mutagenesis was used to replace single or combinations of histidine residues. Functional assays of Cx50 wildtype and mutant hemichannels were examined by electrophysiological techniques in the Xenopus laevis heterologous expression system. Preliminary findings suggest that H95 may not be necessary for pH-dependent channel closure. Attempts to determine if nearby histidine residues could act as redundant sensors were inconclusive due to poor expression levels. I show that removing all three histidine residues resulted in little to no channel activity despite the protein being trafficked to the plasma membrane. Ongoing experiments on these mutants will help identify the structural determinants of pH sensitivity in Cx50 channels.