Journal - Journal of experimental marine biology and ecology

Abstract :

The content of betaine and alanine in gills of the ribbed mussel Geukensia demissa increases rapidly following transfer of the tissues from 250 to 1000 mOsm seawater (SW). Increases in alanine, proline and glycine account for most of the increase in the amino acid pool. The betaine content increases from 45 to 150 &mgr;mol/g dry weight within 12 h. Transfer of isolated gills from 250 to 1000 mOsm SW results in a temporary cessation of all ciliary activity. Within 20-40 min following transfer, ciliary activity has recovered. Recovery of ciliary activity precedes recovery of tissue hydration. The uric acid content of gills is unchanged by exposure to hyperosmotic media, suggesting that uric acid is not a store of nitrogen for alanine synthesis from pyruvate. In other organisms, the accumulation of betaine in response to hyperosmotic stress is a slow (days to weeks) process that probably involves changes in gene expression. The rapid, large increases in betaine reported here suggest that gene expression is not a factor in volume recovery by euryhaline bivalve tissues exposed to acute hyperosmotic stress.

Journal - Journal of morphology (United States )

Abstract :

We examined the morphology and pharmacology of the bulbus arteriosus of the marine bivalve mollusc Mercenaria mercenaria. The bulbus arteriosus is an organ of unknown function associated with the posterior aorta and the ventricle. It is composed of connective tissue interspersed with muscle bundles. In contrast to the lumen of the ventricle, which has an extensive trabecular network, the lumen of the bulbus arteriosus has no trabeculae. No valve is present in the posterior aorta connecting the lumina of the ventricle and the bulbus arteriosus. Scattered neuronal profiles are present in the wall and the axonal processes contain vesicles that may contain neurosecretory products. We did not, however, find synapses or evidence of vesicular release into the lumen of the bulbus arteriosus. The bulbus arteriosus contains acetylcholine, 5-hydroxytryptamine (5HT), and the molluscan neuropeptides FMRFamide (phenyl-alanyl-methionyl-arginyl-phenylalaninylamide) and FLRFamide (phenylalanyl-leucinyl-arginyl-phenylalanylamide). The isolated bulbus arteriosus contracts tonically in response to mechanical stress and exposure to 5HT or FMRFamide, while acetylcholine relaxes it. We surmise that the bulbus arteriosus probably functions as a mechanism for regulating the relative amounts of hemolymph pumped into the anterior and posterior aortae by the ventricle and that the bulbus arteriosus may be a neurohemal site.Copyright 2001 Wiley-Liss, Inc.

Journal - Physiological zoology (UNITED STATES )

Abstract :

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.

Journal - The Journal of experimental zoology (UNITED STATES )