Phosphorylation in the C-terminus of the rat connexin46 (rCx46) and regulation of the conducting activity of the formed connexons

To analyse the role of PKC-dependent phosphorylation in the C-terminus of rCx46 in regulation of rCx46 connexons, truncated mutants rCx46(45.3) and rCx46(44.2) which end before and after PKC-dependent phosphorylation sites respectively were generated. Both rCx46(45.3) and rCx46(44.2) formed connexons in Xenopus oocytes similar to Cx46(wt)-connexons. They were activated by depolarisation above -40 mV and at voltages above 50 mV, inactivation was spontaneously observed or induced by PKC activator TPA, suggesting that inactivation does not require PKC-dependent phosphorylation in the C-terminus. Three casein-kinase-II-(CKII)-dependent phosphorylation sites were also identified. rCx46(37.7) and rCx46(28.2) respectively without two or all of these sites were generated. rCx46(37.7)-connexons were similar to rCx46(wt)-connexons. rCx46(28.2)-connexons comparable to rCx46(wt)-connexons were observed after injection of 50 times more rCx46(28.2)-mRNA (25 ng per oocyte). CKII-blocker inhibited depolarisation-evoked currents in oocytes injected with 0.5 ng per oocyte rCx46(37.7)-mRNA or rCx46(wt)-mRNA. Injection of 25 ng per oocyte rCx46(37.7)-mRNA or rCx46(wt)-mRNA overcame the effect of CKII-inhibitor. We propose that CKII-dependent phosphorylation in the C-terminus accelerates formation of rCx46-connexons.