Aging of cell communication: loss of receptor function.

Communication between cells is the most important evolutionarily conserved mechanism which enabled the bioconstruction of multicellular organisms. These mechanisms all comprise some general properties such as specific receptors recognized by agonists, molecules capable of activating them as well as the intracellular signalling pathways which activate the effector functions. A large number of such receptors and transmission pathways have been described, and both agonists and antagonists have been identified and are used in medicine. A more recent discovery was the demonstration that several receptor-mediated functions decline with age because either of the loss of receptors or their uncoupling from their specific signalling pathways. The mechanisms and biological as well as pathological consequences of this age-dependent receptor loss and signal transduction changes are described in this chapter.