Derek Beahm's Lab Page

I'm currently working on gap junctions. Here is a copy of an abstract I'm doing this summer at a gap junction meeting.

We used the paired Xenopus oocyte expression system to examine the relationship between the number and nature of gap junction precursors and the rate of gap junction formation. We determined the size of the gap junction precursor pool by measuring the number of cx46 hemichannels. The activity (that is the number of open cx46 hemichannels) can be controlled by voltage or calcium concentration. We have found that activation of cx46 hemichannels by depolarization or lowered extracellular calcium concentration dramatically increases the rate of gap junction formation through an unknown mechanism. The increase in gap junctional conductance is associated with a decrease in the number of hemichannels, suggesting that activated hemichannels are recruited to form functional connexons. The time course of the depolarization-stimulated junctional conductance increase is well fit by a single exponential growth curve of the form G(t) = Gmax (1 - exp(-k t)). Gmax is proportional to the number of hemichannels present before activation. Two possible mechanisms could explain the observed phenomenon. First; the activation of cx46 hemichannels could indirectly increase the proximity of the opposing plasma membranes thereby facilitating junctional formation. Second, activation of cx46 hemichannels could convert hemichannels to a precursor state which readily forms gap junctions. To distinguish between these possibilities, we are now investigating the relationship between the number of hemichannels activated during transient activation and the initial rate of increase. We are grateful for the support of NIH grant EY-05661 to JEH