A CHIMERIC CONNEXIN FORMING GAP JUNCTION HEMICHANNELS

Connexins are the subunits of gap junction channels which connect neig hboring cells. With the exception of lens connexins, they usually do n ot form open hemichannels in the cell membrane of single cells. Here w e describe a chimeric connexin consisting of cx32 where the first extr acellular loop sequence is replaced by the corresponding cx43 sequence . This chimera, cx32E(1)43, forms conventional gap junction channels i n the paired oocyte assay. In addition cx32E(1)43 induces a membrane c onductance in single oocytes. This membrane conductance is voltage dep endent and is similarly sensitive to CO2 as are gap junction channels formed by the chimera or by wild-type cx32. These data suggest that cx 32E(1)43 forms patent hemichannels in the plasma membrane of single oo cytes. This conclusion is further supported by the observation that oo cytes expressing cx32E(1)43 take up from the bath medium tracer molecu les known to pass through gap junction channels.