Cell-to-Cell Communication

Abstract

In formulating cell theory, Mathias Schleiden⁽¹⁾ wrote in 1838: “Every higher organism is an aggregate of fully circumscribed and self-contained unit beings, the cells.” This has been one of the most fruitful tenets in biology which—the theory of evolution and the central dogma of molecular biology aside—has had no equal in influencing biological work and thought. The hypothesis held sway for more than a century. But 20 years ago it underwent a basic change when it was found that the cellular circumscription was commonly not complete; many cells turned out to be interconnected at their junctions.^(2,3) The elements in this connection are specialized membrane channels built into the junctional membrane complex, through which a range of mole¬cules can flow from one cell interior to another⁽⁴⁾ (Fig. 1). These cell-to-cell channels provide a degree of continuity between cells, without loss of external circumscription. Commonly, a given cell in a tissue is thus coupled to several neighbors, and so whole organs or large organ parts are continuous from within. It is then the connected cell ensemble, not the single cell, that is the functional compartmental unit in respect to the channel-permeant molecules. The cell is the unit only in regard to the macromolecules that are too large for the channels.