Formation of heteromeric gap junction channels by connexins 40 and 43 in vascular smooth muscle cells

Connexin (Cx) 43 and Cx40 are coexpressed in several tissues, including car diac atrial and ventricular myocytes and vascular smooth muscle. It has bee n shown that these Cxs form homomeric/homotypic channels with distinct perm eability and gating properties but do not form functional homomeric/heterot ypic channels. If these Cxs were to form heteromeric channels, they could d isplay functional properties not well predicted by the homomeric forms. We assessed this possibility by using A7r5 cells, an embryonic rat aortic smoo th muscle cell line that coexpresses Cxs 43 and 40. Connexons (hemichannels ), which were isolated from these cells by density centrifugation and immun oprecipitated with antibody against Cx43, contained Cx40. Similarly, antibo dy against Cx40 coimmunoprecipitated Cx43 from the same connexon fraction b ut only Cx40 from Cx (monomer) fractions. These results indicate that heter omeric connexons are formed by these Cxs in the A7r5 cells. The gap junctio n channels formed in the A7r5 cells display many unitary conductances disti nct from homomeric/homotypic Cx43 or Cx40 channels. Voltage-dependent gatin g parameters in the A7r5 cells are also quite variable compared with cells that express only Cx40 or Cx43. These data indicate that Cxs 43 and 40 form functional heteromeric channels with unique gating and conductance propert ies.