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

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

^*Department of Physiology, Arizona Health Sciences Center, University of Arizona, Tucson, AZ, 85724; ^†Department of Biochemistry, University of Texas Health Science Center, San Antonio, TX, 78284; and ^‡Department of Microbiology and Immunology, State University of New York Health Science Center, Syracuse, NY 13210

Edited by Lily Yeh Jan, University of California, San Francisco, CA, and approved March 31, 1999 (received for review February 10, 1999)

Abstract

Connexin (Cx) 43 and Cx40 are coexpressed in several tissues, including cardiac atrial and ventricular myocytes and vascular smooth muscle. It has been shown that these Cxs form homomeric/homotypic channels with distinct permeability and gating properties but do not form functional homomeric/heterotypic channels. If these Cxs were to form heteromeric channels, they could display functional properties not well predicted by the homomeric forms. We assessed this possibility by using A7r5 cells, an embryonic rat aortic smooth muscle cell line that coexpresses Cxs 43 and 40. Connexons (hemichannels), which were isolated from these cells by density centrifugation and immunoprecipitated with antibody against Cx43, contained Cx40. Similarly, antibody against Cx40 coimmunoprecipitated Cx43 from the same connexon fraction but only Cx40 from Cx (monomer) fractions. These results indicate that heteromeric connexons are formed by these Cxs in the A7r5 cells. The gap junction channels formed in the A7r5 cells display many unitary conductances distinct from homomeric/homotypic Cx43 or Cx40 channels. Voltage-dependent gating 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 properties.

Footnotes

↵ § To whom reprint requests should be addressed at: Department of Physiology, Arizona Health Sciences Center, Room 4103, University of Arizona, 1501 North Campbell Avenue, Tucson, AZ 85724. e-mail: jburt{at}u.arizona.edu.
This paper was submitted directly (Track II) to the Proceedings Office.
ABBREVIATION:

Cx,

connexin