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Oxygen limitation of thermal tolerance - a unifying principle?
Abstracts / Comparative Biochemistry and Physiology, Part B 126 (2000) S1-S108 OXYGEN LIMITATION OF THERMAL TOLERANCE - A UNIFYING PRINCIPLE?
H.O. P6rtner Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, F.R.G. Evidence will be reviewed which indicates that low and high limits of thermal tolerance are set by oxygen limitations in various marine ectotherms of different phyla. At temperatures above or below ambient aerobic scope starts to be reduced. At low temperatures this is indicated by falling oxygen levels in the body fluids in relation to insufficient performance of circulatory or ventilatory mechanisms. At high temperatures falling oxygen levels in the body fluids are linked to rising oxygen demand and, again, insufficient capacities of ventilation and circulation. In accordance with the law of tolerance the onset of a drop in aerobic scope characterizes low and high pejus thresholds. Beyond pejus levels temperature finally reaches a low or a high critical threshold (Tc) where aerobic scope is nil and further cooling or warming causes a transition to an anaerobic mode of mitochondrial metabolism. It will be investigated to what extent these conclusions can be extrapolated to air breathing animals. A goneral view is developed linking the processes and limits of thermal adaptation and thermal tolerance with the adjustment of mitochondriat densities and, thus, aerobic capacity as a crucial event in the thermal adaptation of water breathers. Critical and pejus temperatures shift unidirectionally within, and differ between, pbpulations depending on seasonal temperature acclimatlsation and latitude. An increase of aerobic capacity during cold adaptation and, conversely, a decrease during warm adaptaticmwill, therefore, lead to a concomitant shift of both pejus and both critical temperatures. In addition, the Tc's and the widlh of the tolerance window are likely to be set by the adjustment of kinetic properties of mitochondria, e.g. maximum respiratory as well as lxoton leakage rates and their te~nperature dependence. Adaptation to the permanent cold of polar areas may lead to an increased temperature dependence of mitochondrial oxygen demand, especially proton leakage, and of flux limiting enzymes in metabolism. Considering that aerobic capacity and energy expenditure are minimized according to environmental and lifestyle requirements the hypothesis is developed that costs of maintenance are higher in cold adapted eurytherms than in cold stenothetmal animals. Frederich, M., H.O. P6rtner (2000) Am. J. Physiol. In press ; Sommer, A., H.O. POrtner (1999) Mar. Ecol. Progr. Set. 181,215-226 ; P0rtner, I-LO.et al. (2000) In: Antarctic Ecosystems: models for wider ecological understanding, eds W. Davison, C. Howard Williams; Caxton Press, Christchurch New Zealand, in press.
SURFACE ACTIVITY IN VITRO: ROLE OF SURFACTANT PROTEINS Fred Possmay~P, Kaushik Nag', Karina Rodriguez', Riad Qanbata, and Sam Schfirch3 'Depts. of Ob/Gyn & Biochemistry, University of Western Ontario, London, Canada; 2Universit6 de Montr6al, Montreal, Canada; 3RespiratoryResearch Group, University of Calgary, Calgary, Canada Pattie, who provided the initial direct experimental evidence for pulmonary surfactant, was the first to refer to it as a lipoprotein. The functions of the surfactant proteins (SP-) SP-A, SP-B, and SP-C were investigated using a captive bubble surfactometer. The major lipid systems employed were dipalmitoylphosphatidylcholine(DPPC) and l-palmitoyl,2-oleoyl-phosphatidylcholine(PC) or 1-palmitoyl,2-oleoyl-phosphatidylglycerol(PG). SP-B and SP-C accelerated film formation with both lipid mixtures. In other studies, the surface area reductions required to lower surface tension (y) from 20 mN/m near equilibrium to near 0 mN/m during the fwst quasistatic compression were determined. Surface activities (i.e., abifity to reduce surface tension) in rank order were SP-A+SP-B s SP-B << SP-C << phospholipid alone. Interestingly, with SP-A + SP-B and SP-B, the surface area reductions required to achieve 7 near 0 mN/m with PG.-containing films were less than that predicted for a squeezeout mechanism, whereby fluid lipids are preferentially excluded from the surface area during lateral compression. This indicates SP-B facilitates the selective insertion of DPPC over PG during surfactant adsorption. Surface activity improved during additional quasistatic cycles, indicating SP-B also promotes squeezcout of PG. With PC-containing samples, preferential squeezeout was more limited. Studies using dynamic (continuous) cycles at 25 cycles/minute further demonstrated the superiority of SP-B over SP-C. Dynamic cycling also showed addition of S P A limited the increase in y during film expansion, resulting in superior overall surface activity. The size of the surface-associated surfactant reservoir was determined by subphase washout experiments. This measurement assesses the amount of DPPC-euriched material which can be incorporated into the surface monolayer during surface area expansion. SP-C was superior to SP-B in generating this reservoir. In addition, SP-C was more effective in promoting the reinsertion of lipid into the surface monolayer after overcompression of surface films (i.e., continued surface area reduction once low y was attained). The palmitates associated with the N-terminus of SP-C were critical for reinsertion. These results indicate the surfactant apoproteins possess distinct overlapping functions. SP-B is effective in selective DPPC insertion during monolayer formation and in PG squeezeout during monolayer compression. SP-A can promote adsorption during film formation, particularly in the presence ofSP-B. SP-C appears to have a superior role to SP-B in formation of the surfactant reservoir and in reinsertion of collapse phase lipids.
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H.O. P6rtner Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, F.R.G. Evidence will be reviewed which indicates that low and high limits of thermal tolerance are set by oxygen limitations in various marine ectotherms of different phyla. At temperatures above or below ambient aerobic scope starts to be reduced. At low temperatures this is indicated by falling oxygen levels in the body fluids in relation to insufficient performance of circulatory or ventilatory mechanisms. At high temperatures falling oxygen levels in the body fluids are linked to rising oxygen demand and, again, insufficient capacities of ventilation and circulation. In accordance with the law of tolerance the onset of a drop in aerobic scope characterizes low and high pejus thresholds. Beyond pejus levels temperature finally reaches a low or a high critical threshold (Tc) where aerobic scope is nil and further cooling or warming causes a transition to an anaerobic mode of mitochondrial metabolism. It will be investigated to what extent these conclusions can be extrapolated to air breathing animals. A goneral view is developed linking the processes and limits of thermal adaptation and thermal tolerance with the adjustment of mitochondriat densities and, thus, aerobic capacity as a crucial event in the thermal adaptation of water breathers. Critical and pejus temperatures shift unidirectionally within, and differ between, pbpulations depending on seasonal temperature acclimatlsation and latitude. An increase of aerobic capacity during cold adaptation and, conversely, a decrease during warm adaptaticmwill, therefore, lead to a concomitant shift of both pejus and both critical temperatures. In addition, the Tc's and the widlh of the tolerance window are likely to be set by the adjustment of kinetic properties of mitochondria, e.g. maximum respiratory as well as lxoton leakage rates and their te~nperature dependence. Adaptation to the permanent cold of polar areas may lead to an increased temperature dependence of mitochondrial oxygen demand, especially proton leakage, and of flux limiting enzymes in metabolism. Considering that aerobic capacity and energy expenditure are minimized according to environmental and lifestyle requirements the hypothesis is developed that costs of maintenance are higher in cold adapted eurytherms than in cold stenothetmal animals. Frederich, M., H.O. P6rtner (2000) Am. J. Physiol. In press ; Sommer, A., H.O. POrtner (1999) Mar. Ecol. Progr. Set. 181,215-226 ; P0rtner, I-LO.et al. (2000) In: Antarctic Ecosystems: models for wider ecological understanding, eds W. Davison, C. Howard Williams; Caxton Press, Christchurch New Zealand, in press.
SURFACE ACTIVITY IN VITRO: ROLE OF SURFACTANT PROTEINS Fred Possmay~P, Kaushik Nag', Karina Rodriguez', Riad Qanbata, and Sam Schfirch3 'Depts. of Ob/Gyn & Biochemistry, University of Western Ontario, London, Canada; 2Universit6 de Montr6al, Montreal, Canada; 3RespiratoryResearch Group, University of Calgary, Calgary, Canada Pattie, who provided the initial direct experimental evidence for pulmonary surfactant, was the first to refer to it as a lipoprotein. The functions of the surfactant proteins (SP-) SP-A, SP-B, and SP-C were investigated using a captive bubble surfactometer. The major lipid systems employed were dipalmitoylphosphatidylcholine(DPPC) and l-palmitoyl,2-oleoyl-phosphatidylcholine(PC) or 1-palmitoyl,2-oleoyl-phosphatidylglycerol(PG). SP-B and SP-C accelerated film formation with both lipid mixtures. In other studies, the surface area reductions required to lower surface tension (y) from 20 mN/m near equilibrium to near 0 mN/m during the fwst quasistatic compression were determined. Surface activities (i.e., abifity to reduce surface tension) in rank order were SP-A+SP-B s SP-B << SP-C << phospholipid alone. Interestingly, with SP-A + SP-B and SP-B, the surface area reductions required to achieve 7 near 0 mN/m with PG.-containing films were less than that predicted for a squeezeout mechanism, whereby fluid lipids are preferentially excluded from the surface area during lateral compression. This indicates SP-B facilitates the selective insertion of DPPC over PG during surfactant adsorption. Surface activity improved during additional quasistatic cycles, indicating SP-B also promotes squeezcout of PG. With PC-containing samples, preferential squeezeout was more limited. Studies using dynamic (continuous) cycles at 25 cycles/minute further demonstrated the superiority of SP-B over SP-C. Dynamic cycling also showed addition of S P A limited the increase in y during film expansion, resulting in superior overall surface activity. The size of the surface-associated surfactant reservoir was determined by subphase washout experiments. This measurement assesses the amount of DPPC-euriched material which can be incorporated into the surface monolayer during surface area expansion. SP-C was superior to SP-B in generating this reservoir. In addition, SP-C was more effective in promoting the reinsertion of lipid into the surface monolayer after overcompression of surface films (i.e., continued surface area reduction once low y was attained). The palmitates associated with the N-terminus of SP-C were critical for reinsertion. These results indicate the surfactant apoproteins possess distinct overlapping functions. SP-B is effective in selective DPPC insertion during monolayer formation and in PG squeezeout during monolayer compression. SP-A can promote adsorption during film formation, particularly in the presence ofSP-B. SP-C appears to have a superior role to SP-B in formation of the surfactant reservoir and in reinsertion of collapse phase lipids.
$79