Risultati finali
Gap junction channels maintain cell-cell communication and thus are essential for the functional co-ordination of tissues and organs. These channels are composed of connexins, a membrane protein family with more than a dozen members. Properties of gap junction channels are best studied with connexin deficient cells which are transfected with a selected connexin gene. We investigated connexin transfected HeLa cells with electrophysiological techniques. When Cx26- and Cx32-HeLa transfectants grew as monolayers Lucifer yellow transfer is reduced with increasing cell density and decreasing pH of the medium. The pH sensitivity of Cx43 is influenced by the position rather than by the total number of histidine residues in its cytoplasmic loop. Two uncoupling mechanisms might have been involved: 1. A long lasting downregulation caused by a degradation of gap junction channels in "exhausted" medium. 2. A fast and reversible blockage of junctional conductance caused by shifts in pHi. The fast pHi induced blockage of junctional conductance is independent of [H2CO3] but may be caused by protonation of histidine residues in the cytoplasmic loop. Cx26 transfectants have only one histidine in this domain and uncouple at pHi 7.0, whereas Cx32 transfectants have six histamines and remain coupled till pHi 6.5.
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