A map of the heart: gap junctions, connexin diversity and retroviral studies of conduction myocyte lineage.

1. The heartbeat is co-ordinated by organized propagation of electrical excitation through cardiac muscle. Intercellular conduction and propagation of the cardiac action potential is dependent on electrical connections between myocytes, termed gap junctions. 2. In the last few years, our conception of the structure and function of cardiac gap junctions has been revised substantially. It seems that these structures show unexpected levels of specialization within the myocardium and they can no longer be viewed simply as passive conduits for the regulated movement of electrical current between heart muscle cells. 3. In this article, some of the contributions to this field by the author and his collaborators are summarized. Studies using confocal microscopy and digital imaging techniques to characterize the three-dimensional organization of electrical contacts between myocytes in the mature and developing heart are described, data on the unique expression and spatial distribution patterns of gap-junctional subunit proteins (connexins) are given, and finally the author's current work on the differentiation of cardiac conduction tissues, and how this work arose from studies of gap junctions in the heart, is introduced.