Comparative Biochemistry and Physiology Part A: Physiology最新文献

The structural and functional organization of digestive-transport surfaces in some lower cestodes and their fish hosts was studied. It has been shown that the ultrastructure of cestode microtriches and fish enterocyte microvilli being the basis of membrane-linked digestion is quite similar. These organelles increase the digestive-transport surfaces both in helminths and fishes. However, the hydrolytic enzyme activity in helminths is usually 2–4 times lower than that of the fishes. Desorption (adsorption) characteristics of various hydrolases in helminths and fishes are also different. In helminths the easily desorbed fraction of each enzyme is always more abundant than in fishes. In contrast, the intensity of transport processes in helminths is higher when compared with fishes. The adaptation of digestive-transport surfaces and enzyme systems to feeding conditions is discussed.

The uptake of choline by the tegument of Hymenolepis diminuta was investigated. The Q₁₀ at pH 7.0 was 1.7, with an Ea of 90 kJ·mol⁻¹. Choline transport was pH sensitive: At pH 5.0, a Na⁺-independent mechanism predominated, which was inhibited by 100 nM benzamil, 130 mM Na⁺, and 300 μM verapamil. At pH 7.0, the Na⁺-independent mechanism was inhibited by 130 mM Na⁺, amiloride, and EIPA with IC₅₀'s of 130 μM and 30 μM, respectively, and by benzamil with IC₅₀'s of 100 pM (high-potency Benzamil Sensitive Component; HBSC) and 70 μM (low-potency Benzamil Sensitive Component; LBSC). Calcium-free saline enhanced choline uptake non-specifically. Lanthanum³⁺, Gd³⁺, gramicidin, nigericin, and high-K⁺ did not affect choline uptake at pH 5.0 or pH 7.0, and 10 μM verapamil was without effect at pH 5.0, suggesting no significant role for the electrical potential difference across the brush-border membrane, a $\text{Na}{}^{\mathrm{+}}\text{H}{}^{\mathrm{+}}$ antiporter, a $\text{Na}{}^{\mathrm{+}}\text{Ca}{}^{\mathrm{2+}}$ antiporter, or Ca²⁺ channels in choline uptake. Under physiological conditions, the HBSC accounts for ∼25% of the total choline taken up at pH 5.0, while the LBSC accounts for ∼55% of the choline taken up at pH 7.0. The data suggest novel choline transporting mechanisms; an HBSC which displays properties in common with apical Na⁺ channels, and a unique LBSC of choline transport.

The forest shrew (Myosorex varius) is grouped with the subfamily Crocidurinae, but recent allozyme evidence suggests that it is intermediate between the Crocidurinae and the Soricinae. It also exhibits some atypical morphological features. Because the two subfamilies have different habits and levels of metabolism, we measured activity patterns, metabolism and thermoregulation of M. varius to assess whether its physiology was consistent with that of the other crocidurines. Metabolic rate within the thermal neutral zone (29–35°C) averaged 38.9 J g⁻¹hr⁻¹, close to expected levels for a mammal of equivalent size. Body temperatures were quite variable, ranging from 33.2–38.3°C and were defended at temperatures as low as 6°C by increased beat production. These data suggest that M. varius is a typical crocidurine. In contrast to other crocidurines, however, M. varius did not enter torpor. They also exhibit differences in their winter activity patterns and may be territorial, suggesting that at least in some respects M. varius does differ from other crocidurines.

Facultative metabolic rate depression is the common adaptive strategy underlying various animal mechanisms for surviving harsh environmental conditions. This strategy is common among molluscs, enabling animals to survive over days or even months in the absence of oxygen or undr extremely dry conditions. The large reductions in metabolic rate during estivation and anoxia can translate into considerable energy savings when dormant animals are compared to active animals. A complex metabolic coordination is required during the transition into the dormant state to maintain cellular homeostasis and involves both energy-consuming and energy-producing pathways. With regard to energy-producing pathways, several different mechanisms have been identified that participate in controlling flux. One such mechanism, enzyme phosphorylation, can have a wide-ranging effect. For example, phosphorylated enzymes exhibit altered substrate, activator, and inhibitor affinities. This effect may be magnified by changes in the concentrations of allosteric effectors, such as fructose 2,6-bisphosphate, that occur during hypometabolic states. Changes in fructose 2,6-bisphosphate are related to changes in enzyme phosphorylation through changes in the relative activity of phosphofructokinase-2. Alterations in glycolytic enzyme binding can also be brought about through changes in enzyme phosphorylation. The present review focuses on identifying hypometabolism-related changes in enzyme phosphorylation as well as characterizing the mechanisms involved in mediating these phosphorylation events.

Survival, oxygen consumption, locomotory activity and ventilatory activity were recorded during a 180-day starvation period and a subsequent 15-day feeding phase in 3 hypogean crustaceans, Niphargus rhenorhodanensis, Niphargus virei, and Stenasellus virei. For comparison, these parameters were also recorded during a 28-day starvation period and a subsequent 7-day feeding phase in two morphologically close epigean crustaceans, Gammarus fossarum and Asellus aquaticus.

Hypogean crustaceans were better adapted to lack of food than epigean ones and all crustaceans previously studied, with survival times largely longer than 200 days. During long-term starvation, the locomotory, ventilatory, and respiratory rates were drastically lowered in subterranean species, whereas surface species showed lower decreases in these rates and responded by a marked and transitory hyperactivity. The higher reduction in metabolic rate by hypogean species would ensure their survival during prolonged periods of food deprivation.

We propose an energy strategy for food-limited hypogean crustaceans involving the ability 1) to withstand long-term starvation, and 2) to use the consumed food very efficiently. Resistance to starvation would probably involve a state of temporary torpor during which the subterranean crustaceans subsist on a high energy reserve, such as lipid stores.

The slow, spontaneous release of hemin from earthworm, Lumbricus terrestris, hemoglobin has been studied under mild conditions in the presence of excess apomyoglobin. This important protein is surprisingly unstable. The reaction is best described as hemin released from the globin into water, followed by quick engulfment by apomyoglobin. The energetics of this reaction are compared with those of other types of hemoglobins. Anomalously low activation energy and enthalpy are counterbalanced by a negative entropy. These values reflect significant low frequency protein motion and dynamics of earthworm hemoglobin and may also indicate an open structure distal to the heme. This is also supported by the infrared spectrum of the carbonyl hemoprotein, which indicates several types of distal interactions with the bound CO. The reported low heme to polypeptide ratio for this protein may be due to facile heme and hemin release by the circulating protein.

Feral and domestic honey bees were compared to determine relative levels of adaptation to the Arizona desert. Feral honey bees were more tolerant to high temperatures than domestic honey bees. Monthly critical thermal maxima (CTMs) of feral bees were significantly different from those of domestic bees (P < 0.001). The highest mean CTM for feral bees was 50.7 ± 1.0°C, and for domestic honey bees was 42.8 ± 2.8°C; both were recorded in June 1991. There was also a significant effect of sampling date on CTMs (P < 0.0001). Water loss increased with increasing temperature and with decreasing humidity for both feral and domestic honey bees. The rates of water loss for both types of bees were highest in dry air (0% relative humility) at 35°C, with the average value of 6.82 ± 0.33 mg/g/hr for domestic bees. At 35°C, the rate of water loss of feral bees was more than twice that at 25°C (5.94 compared with 2.37 mg/g/hr). Water losses for feral and domestic honey bees were not significantly different; therefore, rates of water loss do not explain the higher temperature tolerance of feral honey bees.