DIFFERENTIAL REGULATION OF DISTINCT TYPES OF GAP JUNCTION CHANNELS BYSIMILAR PHOSPHORYLATING CONDITIONS

Studies on physiological modulation of intercellular communication med iated by protein kinases are often complicated by the fact that cells express multiple gap junction proteins (connexins; Cx). Changes in cel l coupling can be masked by simultaneous apposite regulation of the ga p junction channel types expressed. We have examined the effects of ac tivators and inhibitors of protein kinase A (PKA), PKC, and PKG on per meability and single channel conductance of gap junction channels comp osed of Cx45, Cx43, or Cx26 subunits. To allow direct comparison betwe en these Cx, SKHep1 cells, which endogenously express Cx45, were stabl y transfected with cDNAs coding for Cx43 or Cx26. Under control condit ions, the distinct types of gap junction channels could be distinguish ed on the basis of their permeability and single channel properties. U nder various phosphorylating conditions, these channels behaved differ ently. Whereas agonists/antagonist of PKA did not affect permeability and conductance of all gap junction channels, variable changes were ob served under PKC stimulation. Cx45 channels exhibited an additional co nductance state, the detection of the smaller conductance states of Cx 43 channels was favored, and Cx26 channels were less often observed. I n contrast to the other kinases, agonists/antagonist of PKG affected p ermeability and conductance of Cx43 gap junction channels only. Taken together, these results show that distinct types of gap junction chann els are differentially regulated by similar phosphorylating conditions . This differential regulation may be of physiological importance duri ng modulation of cell-to-cell communication of more complex cell syste ms.