EASTERN Oyster Crassostrea virginica heart rates associated with differing oxygen concentrations as measured by minimally invasive electrocardiography.

Eastern oysters (Crassostrea virginica) are well known for their ability to tolerate low oxygen tensions. However, the physiological and biochemical mechanisms responsible for this tolerance are poorly understood. Many studies have focused on the biochemical changes that occur with anoxia, including the accumulation of succinate and alanine as shifts occur in glycolysis and the Krebs cycle to maximize ATP production and minimize the production of potentially toxic end products such as lactate. While alternate ATP production pathways may be partially understood, aerobic metabolism is also reduced. The mechanisms by which tissues maintain the cellular integrity (eg osmotic balance) are unknown. Most previous studies on bivalve hearts have been conducted using tissue-damaging half shell preparations wherein one valve is carefully removed and the heart attached physically to a force transducer to measure contraction strength and frequency. We have developed a minimally invasive preparation in which three small holes are drilled at specific points through one valve.  Electrocardiograph leads are then inserted into the hole and sealed with silicone wax. The resulting prep allows the measurement of heart rate in an intact bivalve allowing us to measure heart rate as a function of environmental conditions over a much longer period of time and observe recovery from experimental manipulations. Our initial studies have shown that the heart rate declined with oxygen tensions, was greatly reduced by anoxia, and typically recovered when normoxic conditions return. This preparation may allow the study of a variety of environmental conditions on oyster physiology.