Closing the gap in understanding the regulation of intercellular communication
Authors: J Saffitz
Journal: Cardiovascular Research (2000)

See article by Van Rijen et al. [2] ( pages 941 -951) inregarded in the context of the larger picture of gap junction this issue.channel diversity.At least 13 members of the connexin family of gap junction channel proteins have been cloned Of the various ways that cells 'talk' to one another, and sequenced [1].As a general rule, each connexin is intercellular communication via gap junctions is certainly expressed in multiple tissues, and individual cells express the most direct.Composed of arrays of densely packed more than one connexin.At least three connexins are channels that link the cytoplasmic compartments of neigh-expressed in the mammalian heart -connexin43 (Cx43), boring cells, gap junctions provide a direct route by which connexin45 (Cx45) and connexin40 (Cx40) -but in cells can exchange ions and small molecules (up to |1 kDa different amounts and combinations in different regions of in mass) [1].Different patterns and distributions of gap the heart.Cx43 is expressed in many tissues and is present junctions between like and disparate cell types may create throughout the heart including atrial and ventricular musboth preferential communication pathways and communi-cle, and most if not all components of the conduction cation boundaries within a tissue or organ.In the heart, gap system.In contrast, expression of Cx40 in the adult junctions are responsible for intercellular transfer of cur-mammalian heart is restricted to atrial muscle and the rent and, thus, control the precise spatiotemporal pattern of cardiac conduction system.Cx40 is also expressed in the electrical activation to coordinate the contractile activities lung and in vascular smooth muscle cells and endothelium. of individual cells and ensure effective pump function.The expression of multiple connexins by individual cells in Gap junctional coupling has traditionally been regarded a given tissue raises the distinct possibility that single as a 'passive' electrophysiological property of heart muscle channels may be composed of more than one connexin.which, like cell size and shape, functions as an importantBecause each cell's contribution to a complete channel determinant of impulse propagation but one not subject to consists of a hemi-channel (referred to as a connexon) active regulation, at least not in the way that ion channels containing six connexin subunits, the potential number of responsible for depolarization and repolarization undergo unique 'hybrid' connexons and channels is truly vast [1].rapid transitions in functional state during the cardiac Little is known about the natural occurrence or biological cycle.We now know that this outmoded view of gap significance of hybrid channels in vivo, but a great deal of junction channels is inaccurate.Rather than being fixed work involving in vitro expression systems has clearly passive conduits, gap junction channels are, in fact, demonstrated that single channels composed of more than regulated by complex mechanisms that are only now being one connexin subunit type can form and may exhibit identified.A paper in the current issue of Cardiovascular distinct biophysical properties. Research by van Rijen et al. [2] adds new information toThe potential diversity of gap junction channel types the increasingly complex picture of regulation of inter-raises major questions about the biological purposes cellular communication at gap junctions.subserved by expression of multiple connexins in the heart.The contribution by van Rijen et al.[2] must be Insights have been gained recently through studies of mice in which the expression of one or more connexins has been manipulated genetically.Modest slowing of ventricular