Connexin expression systems: to what extent do they reflect the situation in the animal?

Intercellular communication is mediated by specialized cell-cell contact areas known as gap junctions. Connexins are the constitutive proteins of gap junction intercellular channels. Various cell expression systems are used to express connexins and, in turn, these expression systems can then be tested for their ability to form functional cell-cell channels. In this review, expression of murine endogenous connexins in primary cells and established cell lines is compared with results obtained by expression of exogenous connexins in Xenopus oocytes and cultured mammalian cells. In addition, first reports on characterization of connexin-deficient mice are discussed.