Submitted on March 24, 2009
Revised on May 6, 2009
Accepted on May 20, 2009
Regulation of gap junctional charge selectivity in connexin 40 and connexin 43 co-expressing cells
Nathanael S Heyman1, David T Kurjiaka, Jose F Ek Vitorin1, and Janis M. Burt2*
1 University of Arizona
2 University of Arizona College of Medicine
* To whom correspondence should be addressed. E-mail: jburt{at}u.arizona.edu.
Expression of connexin 40 (Cx40) and Cx43 in cardiovascular tissues varies as a function of age, injury and development with unknown consequences on the selectivity of junctional communication and its acute regulation. We investigated the PKC-dependent regulation of charge selectivity in junctions composed of Cx43, Cx40, or both by simultaneous assessment of junctional permeance rate constants (Bdye) for dyes of similar size but opposite charge, NBD-M-TMA (+1) and Alexa 350 (-1). Cx40 junctions were cation selective (BNBD-M-TMA/BAlexa 350: 10.7±0.5) whereas Cx43 junctions were non-selective (1.22±0.14). In co-expressing cells, a broad range of junctional selectivities was observed with mean cation-selectivity increasing as the Cx40 to Cx43 expression ratio increased. PKC activation reduced or eliminated dye permeability of Cx43 junctions without altering their charge selectivity, had no effect on either permeability or charge selectivity of Cx40 junctions, and significantly increased the cation selectivity of junctions formed by co-expressing cells (approaching charge selectivity of Cx40 junctions). Junctions composed of Cx43 truncated at residue 257 (Cx43tr) were also not charge-selective, but when Cx43tr was co-expressed with Cx40, a broad range of junctional selectivities that was unaffected by PKC activation was observed. Thus, whereas the charge selectivities of homomeric/homotypic Cx43 and Cx40 junctions appear invariant, the selectivities of junctions formed by cells co-expressing Cx40 and Cx43 vary considerably, reflecting both their relative expression levels and phosphorylation-dependent regulation. Such regulation could represent a mechanism by which co-expressing cells such as vascular endothelium and atrial cells regulate acutely the selective intercellular communication mediated by their gap junctions.
