Comparative aspects of cellular-volume regulation in cardiomyocytes

All cells possess mechanisms that are responsible for the maintenance of cellular volume under isosmotic conditions. In addition, many cells are able to adjust cellular volume when incubated in hypo- or hyperosmotic media. Much of the work on cellular-volume regulation has been done on epithelial cells, blood cells, or lines of cultured cells; cardiac muscle has received comparatively little attention. It seems probable that some aspects of cellular-volume regulation in cardiomyocytes vary from those present in other cell types because of the mechanisms associated with the excitability and contractility of cardiac muscle. For example, in myogenic hearts, the role of membrane ion channels in pacemaker potentials complicates models that implicate ion channels as mechanisms for volume regulation. Similarly, models for the initiation and control of volume regulation that rely on changes in cytosolic Ca2+ levels may not be applicable to cardiac muscle, where each action potential and contraction involves the release of Ca2+ from internal stores and a significant influx of Ca2+ across the plasma membrane. A review of the available data on volume regulation in cardiac muscle from a variety of invertebrate and vertebrate species suggests that many features of the current models proposed for the initiation and control of cellular-volume regulation are not compatible with the physiology of cardiac muscle. There are large gaps in our knowledge about volume regulation in cardiac muscle, and further investigation is clearly necessary to enhance our understanding of this aspect of cardiomyocyte physiology.