oxidative stress and cell damage under physiological conditions, but when salines are used that mimic pathological conditions, HBO induces oxidative stress with more ROS formation and cell damage. However, this occurs without clear changes in nitric oxide and vascular endothelial growth factor production. The effects of HBO on Ca 2+ spikes and DNA damage (comet assay) in endothelial cells are also discussed. doi:10.1016/j.cbpa.2008.04.297 A7.12 Age-dependent remodelling of the sinoatrial node J. Yanni, J. Tellez, H. Dobrzynski, M. Boyett (University of Manchester) Ageing is associated with a decline in the function of the sinoatrial node (SAN; e.g. there is decrease in intrinsic heart rate). We investigated the effect of ageing on ion channels in the SAN using young and old (3 and 25 months of age) WistarHanover rats. Extracellular potentials recorded from isolated SAN/atrial preparations showed that, in the older rats, the spontaneous cycle length (CL) was greater (24%). HCN4 and Na v 1.5 mRNA and protein were measured using quantitative PCR and immunohisto- chemistry. Block of HCN4 by 2 mM Cs + caused a significantly greater increase in CL in old rats (22% in young and 45% in old). HCN4 (mRNA and protein) was expressed in the SAN (but not in atrium). There was no age- dependent change in its density. Block of Na v 1.5 by 2 μM TTX caused a significantly greater increase in CL in old rats (11% in young and 37% in old). Na v 1.5 (protein) was expressed in the atrium, but not in the SAN. Furthermore, the volume of HCN4 positive/Na v 1.5-negative SAN tissue increased significantly (by 97%) from young to old. There was no age- dependent change in the Tbx3 mRNA. In the SAN there was also a significant age-dependent decrease in collagen types I and III mRNA and a significant increase of transforming growth factor b1 in the SAN and a significant increase in tumour necrosis factor a in the atrium. We conclude that age-dependent change in ion channels and extracellular matrix in the SAN may be involved in the age-dependent decline in its function. doi:10.1016/j.cbpa.2008.04.298 A7.13 Oxygenation-dependency of nitrite transport and nitric oxide formation in carp and rabbit erythrocytes S. Rohde, F. Jensen (University of Southern Denmark) Nitrite has been suggested to participate in blood flow regulation by reacting with deoxygenated hemoglobin (Hb) to form nitric oxide (NO). We have investigated the transport of nitrite and its reaction with Hb at different oxygen saturations (So 2 ) in intact erythrocytes from carp and rabbit. Erythrocyte suspensions were equilibrated to different Po 2 values at physiological Pco 2 , and nitrite was added to high (3 mM) or low (0.1 mM) extracellular concentrations to initiate its influx into the erythrocytes. Reaction products were evaluated by spectral deconvolu- tion. In carp, nitrite selectively entered erythrocytes with low and intermediate So 2 values, whereas it hardly entered oxygenated erythro- cytes. In deoxygenated cells, nitrite initially reacted with deoxyHb to produce NO (detected as nitrosylhemoglobin, HbNO) and methemoglo- bin in a 1:1 relationship. Later, metHb was lowered by metHb reductase activity, whereas HbNO continued to rise. HbNO formation was significant at intermediate So 2 , but lower than in fully deoxygenated cells. In rabbit, nitrite influx was the same in oxygenated and deoxygenated erythrocytes at low [NO 2 - ], whereas an intermediate So 2 increased influx. At high [NO 2 - ], nitrite entered oxygenated erythrocytes much faster than deoxygenated erythrocytes, because the nitrite reaction with oxyHb quickly entered the autocatalytic phase, which removed intracellular nitrite (promoting its further entry) and raised metHb to high levels. The formation of NO and HbNO at low So 2 was slower and lower in rabbit than in carp erythrocytes. It is concluded that nitrite transport and NO formation depends on multiple factors, including species-specific differences in membrane permeability, reaction rates and [NO 2 - ]. doi:10.1016/j.cbpa.2008.04.299 A7.14 NO increases myocardial efficiency in the hypoxic tolerant turtle Trachemys scripta M. Misfeldt, A. Fago, H. Gesser (Department of Biological Sciences, University of Aarhus) In the heart, nitric oxide (NO) may influence mechanical perfor- mance relative to oxygen consumption (i.e. efficiency) by competing with oxygen at the level of cytochrome c oxidase and by affecting the amount of Ca 2+ in the excitation–contraction coupling. Such effects of NO are of particular importance when oxygen availability is limited, a condition that is experienced by the highly hypoxic tolerant turtle, Trachemys scripta. We have studied the effects of endogenous NO on the myocardial efficiency of this species. In the presence of L-Arg, the substrate for nitric oxide synthase, the myocardial efficiency of heart ring preparations increased by about 15% during full oxygenation and by about 60% during hypoxia, an effect that was primarily due to a decrease in oxygen consumption. This drop in oxygen consumption was not compensated by an increase in anaerobic glycolysis, as lactate produc- tion during hypoxia did not differ between preparations treated with either L-Arg or ADMA, an inhibitor of nitric oxide synthase. The addition of ADMA did not reverse the effects of L-Arg in these experiments, but pretreatment with ADMA abolished the effect of L-Arg. Histochemical studies using DAF-2DA showed that NO was produced only in the presence of L-Arg. In conclusion, NO may downregulate oxygen consumption without significantly affecting either lactate production or developed force, thereby increasing the efficiency in the turtle myocardium, an effect that is more evident during hypoxia. doi:10.1016/j.cbpa.2008.04.300 A7.15 cGMP-independent nitric oxide modulation of the Frank–Starling response in the eel Anguilla anguilla S. Imbrogno, C. Adamo, F. Garofalo, M.C. Cerra, B. Tota (University of Calabria) The Frank–Starling response is a fundamental property of the vertebrate hearts, which allows the ventricle to respond to increased venous return (preload) with a more vigorous contraction of the lengthened myocardial fibres, hence performing more work and increasing stroke volume. In mammals, myocardial stretch increases cardiac nitric oxide (NO) release from both vascular endothelium and S127 Abstracts / Comparative Biochemistry and Physiology, Part A 150 (2008) S124–S129