Aims: 

In the tissues of the cardiovascular system, adjacent cells are functionally coupled by means of gap junction channels (GJC), predominantly made of the connexins C×37, C×40, C×43 and C×45. Diffusional coupling (signalling molecules, metabolites) and electrical coupling (ions) via GJCs are essential for the tissue homeostasis and the impulse propagation. The purpose of this presentation is to elaborate on the biophysical properties of these channels. Methods: Gap junctions (GJ) can be studied in terms of electrical (conductance) or diffusional properties (permeability). Hence, a voltage-clamp technique or a fluorescence detection method, respectively, has been used to perform experiments on cell-pair preparations. Results: Co-expression of more than one type of connexin renders it possible to form different classes of channels (homomeric-homotypic, homomeric-heterotypic, heteromeric-homotypic, heteromeric-heterotypic). The electrical properties of different types of channels will be described at the multichannel and single-channel level. The data gathered led to a generalized electrical model for GJs and GJCs. The diffusional properties of GJCs are less well studied. While earlier investigations focused on all-or-nothing responses, more recent studies have been aimed at quantitative properties. Currently, data are available for homotypic channels only. Conclusion: Up-to-date methods enable accurate determinations of the biophysical properties of GJs and GJCs. It turns out that structurally different GJCs exhibit functionally different properties. Conceivably, GJCs possess diverse molecular mechanisms designed to adjust the cell-to-cell transfer properties to the actual biological requirements.

Supported by the SNSF (grant 3100A0-108175)