The pore of connexin hemichannels
Date of Award
Doctor of Philosophy (Ph.D.)
Physiology and Biophysics
First Committee Member
Gerhard Dahl - Committee Chair
Gap junction channels are intercellular channels that mediate the gated transfer of molecules between adjacent cells. To identify the domain(s) that determine the permeability of the connexin hemichannel, a domain exchange approach was used. Two connexins, cx46 and cx32E143, that were known to differ in channel conductance by a factor of five were chosen. We found that they also differ in permeability for test molecules, various sized sugars. The first transmembrane segment (M1) was exchanged between these connexins and the resulting chimeras were tested for their permeability properties.The permeability of the connexin channels was tested using sugar molecules, including sorbitol (5.8 A), sucrose (8.9 A) and stachyose (12 A). Sugars were applied to single connexin hemichannel contained in an excised membrane patch to test for accessibility. The transfer rates of sugar molecules through the connexin channel were determined by measuring the uptake of sugar isotopes by oocytes injected with the respective connexin mRNA.The data showed that the permeability of the connexin channel could be transferred between connexins by exchange of the M1. The exchange in either direction, from cx46 to cx32 or from cx32 to cx46, yielded consistent results. Extension of this approach with cx37 as M1 donor increased the conductance and permeability of the M1 recipient, cx46, significantly. Similarly, a point mutation of the critical leucine in position 35 of cx46 to glycine yielded a channel with increased permeability.These data demonstrated the M1 contained determinants of permeability of the connexin channel. A good correlation between conductance and permeability was observed in connexins tested in the present study.
Biology, Animal Physiology
Ma, Meiyun, "The pore of connexin hemichannels" (2005). Dissertations from ProQuest. 2274.