. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. PRESSURE EFFECTS IN B THERMYDRON 213 S O M S V 28 Control 62 28 Recovery Pressure (MPa) Figure 3. Average standard deviation of the intervals between 10 successive contractions of the ventricle ofBythograea thermydron before, during, and after hyperbaric exposure at 5°, 10°. and 20°C. Interbeat variability increased markedly in crabs exposed to 62 MPa pressure at both 5° and 10°C (F = P < and F = P < , respectively): however, variability remained much higher after ret
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. PRESSURE EFFECTS IN B THERMYDRON 213 S O M S V 28 Control 62 28 Recovery Pressure (MPa) Figure 3. Average standard deviation of the intervals between 10 successive contractions of the ventricle ofBythograea thermydron before, during, and after hyperbaric exposure at 5°, 10°. and 20°C. Interbeat variability increased markedly in crabs exposed to 62 MPa pressure at both 5° and 10°C (F = P < and F = P < , respectively): however, variability remained much higher after return to normal pressure in crabs tested at the lower temperature. The interbeat interval also increased significantly in response to hyperbaric exposure at 20°C (F = , P< ). although the change was much less dramatic and recovery more complete than at 5° or 10°C. Error bars represent 1 SEM. were less pronounced at lower temperatures. The change in heart rate accompanying decompression was, in fact, negligible at 5°C (Mickel and Childress, 1982a; Fig. 1). In contrast, the present study clearly demonstrates that higher temperatures reduce the severity of bradycardia resulting from hyperbaric exposure as well as limit the associated disorganization of the contraction waveform. If the primary effects of pressure variation on cardiac function were enzymatically mediated, then one would expect that temperature changes would have comparable effects on cardiac function under both hypo- and hyper- baric conditions. Conversely, if the system affected by pressure challenge is lipid-based. then a decrease in pres- sure (which decreases the viscosity of phospholipid mem- branes) would be compensated by a temperature reduction (causing an increase in membrane viscosity), whereas in- creased pressure would be counteracted by a temperature increase. The latter type of pressure-temperature inter- action has now been shown to occur in response to both hypo- and hyperbaric expo
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