Gap Junctions Flashcards
2 Exceptions of “Gap Junctions b/w All Cells”
Free floating blood cells and adult skeletal muscle fibers
2 Important Gap Junctions b/w Different Cells
Oocyte-follicle cells and spermatogonia-sertoli cells
Pannexins
Share homology to invertebrate innexins, but not really gap junctions, instead on free membrane surface and serve as ATP release channels
Structure of Gap Junctions (3)
2 Hexameric connexons (six subs or connexins) docked to each other (thus a dodecamer)
Connexins have 4 TM segments and 2 EC loops
Homomeric vs. Heteromeric
Connexon formed by six identical or different connexin subs
Homotypic vs. Heterotypic
2 identical or different connexons dock
Connexin Compatibility Example
Cx37 from oocyte can dock with Cx43 on follicle cells, allowing nutrients to reach oocyte
Connexin Incompatibility Example
Cx32 on mammary epithelials that make milk can’t dock with surrounding myoepithelial Cx43 necessary to respond to oxytocin for contraction. Signal would get too diluted and wouldn’t reach threshold for myoepithelials
Formula to Calculate Junctional Conductance in Double Voltage Clamp/Current Circuit
g = i/V
Formula for Junctional Conductance
g = n x P(open) x single channel conductance
2 Gates of Connexin Channels
Docking gate and channel gates
3 Functions of Gating
Rectification in electrical synapses
Change of selectivity by Voltage gate
Uncoupling of dying cells (survive heart attacks) by pH, Ca2+
Cx43 Expression
Gene contains E and P response elements in promoter region, so these hormone fluctuations prior to labor (especially increased E) cause increased luciferase activity, increasing gap junctions in myometrium so they’ll contract during labor and not before
Charcot-Marie-Tooth Disease
Mut in Cx32 (most commonly) that is the gap junction between cytoplasmic folds of Schwann cells so you get neuropathy and wasting away of muscles mainly in limbs
Oculodentodigital Dysplasia
Muts of Cx43 w/ dysplasias of eyes, teeth, and digits
