Journal of Comparative Physiology B最新文献

Abstract

The European corn borer (Ostrinia nubilalis, Hbn.), enters diapause, a strategy characterized by arrest of development and reproduction, reduction of metabolic rate and the emergence of increased resistance to challenging seasonal conditions as low sub-zero winter temperatures. The aim of this study was to investigate the potential role of inorganic elements in the ecophysiology of O. nubilalis, analysing their content in the whole body, hemolymph and fat body, both metabolically active, non-diapausing and overwintering diapausing larvae by ICP-OES spectrometer following the US EPA method 200.7:2001. O nubilalis as many phytophagous lepidopteran species maintain a very low extracellular sodium concentration and has potassium as dominant cation in hemolymph of their larvae. Changes in hemolymph and the whole body sodium content occur already at the onset of diapause (when the mean environmental temperatures are still high above 0 ºC) and remain stable during the time course of diapause when larvae of this species cope with sub-zero temperatures, it seems that sodium content regulation is rather a part of diapausing program than the direct effect of exposure to low temperatures. Compared to non-diapausing O. nubilalis larvae, potassium levels are much higher in the whole body and fat body of diapausing larvae and substantially increase approaching the end of diapause. The concentration of Ca, Mg, P and S differed in the whole body, hemolymph and fat body between non-diapausing and diapausing larvae without a unique trend during diapause, except an increase in their contents at the end of diapause.

Hibernation is a widespread metabolic strategy among mammals for surviving periods of food scarcity. During hibernation, animals naturally alternate between metabolically depressed torpor bouts and energetically expensive arousals without ill effects. As a result, hibernators are promising models for investigating mechanisms that buffer against cellular stress, including telomere protection and restoration. In non-hibernators, telomeres, the protective structural ends of chromosomes, shorten with age and metabolic stress. In temperate hibernators, however, telomere shortening and elongation can occur in response to changing environmental conditions and associated metabolic state. We investigate telomere dynamics in a tropical hibernating primate, the fat-tailed dwarf lemur (Cheirogaleus medius). In captivity, these lemurs can hibernate when maintained under cold temperatures (11–15 °C) with limited food provisioning. We study telomere dynamics in eight fat-tailed dwarf lemurs at the Duke Lemur Center, USA, from samples collected before, during, and after the hibernation season and assayed via qPCR. Contrary to our predictions, we found that telomeres were maintained or even lengthened during hibernation, but shortened immediately thereafter. During hibernation, telomere lengthening was negatively correlated with time in euthermia. Although preliminary in scope, our findings suggest that there may be a preemptive, compensatory mechanism to maintain telomere integrity in dwarf lemurs during hibernation. Nevertheless, telomere shortening immediately afterward may broadly result in similar outcomes across seasons. Future studies could profitably investigate the mechanisms that offset telomere shortening within and outside of the hibernation season and whether those mechanisms are modulated by energy surplus or crises.

Abstract

In salivary acinar cells, cholinergic stimulation induces elevations of cytosolic [Ca²⁺]_i to activate the apical exit of Cl⁻ through TMEM16A Cl⁻ channels, which acts as a driving force for fluid secretion. To sustain the Cl⁻ secretion, [Cl⁻]_i must be maintained to levels that are greater than the electrochemical equilibrium mainly by Na⁺-K⁺-2Cl⁻ cotransporter-mediated Cl⁻ entry in basolateral membrane. Glucose transporters carry glucose into the cytoplasm, enabling the cells to produce ATP to maintain Cl⁻ and fluid secretion. Sodium–glucose cotransporter-1 is a glucose transporter highly expressed in acinar cells. The salivary flow is suppressed by the sodium–glucose cotransporter-1 inhibitor phlorizin. However, it remains elusive how sodium–glucose cotransporter-1 contributes to maintaining salivary fluid secretion. To examine if sodium–glucose cotransporter-1 activity is required for sustaining Cl⁻ secretion to drive fluid secretion, we analyzed the Cl⁻ currents activated by the cholinergic agonist, carbachol, in submandibular acinar cells while comparing the effect of phlorizin on the currents between the whole-cell patch and the gramicidin-perforated patch configurations. Phlorizin suppressed carbachol-induced oscillatory Cl⁻ currents by reducing the Cl⁻ efflux dependent on the Na⁺-K⁺-2Cl⁻ cotransporter-mediated Cl⁻ entry in addition to affecting TMEM16A activity. Our results suggest that the sodium–glucose cotransporter-1 activity is necessary for maintaining the oscillatory Cl⁻ secretion supported by the Na⁺-K⁺-2Cl⁻ cotransporter activity in real time to drive fluid secretion. The concerted effort of sodium–glucose cotransporter-1, Na⁺-K⁺-2Cl⁻ cotransporter, and apically located Cl⁻ channels might underlie the efficient driving of Cl⁻ secretion in different secretory epithelia from a variety of animal species.