ion homeostasis Dotaz Zobrazit nápovědu
Alfred Benzon Symposium III
479 s. : il.,tab.
- MeSH
- amiodaron aplikace a dávkování farmakokinetika terapeutické užití MeSH
- antiarytmika MeSH
- blokátory kalciových kanálů MeSH
- blokátory sodíkových kanálů MeSH
- homeostáza MeSH
- hormony štítné žlázy MeSH
- sodíkové kanály MeSH
- subcelulární frakce účinky léků MeSH
- thyreostatika MeSH
- Publikační typ
- přehledy MeSH
Adults of warm- and cold-acclimated tropical cockroaches, Nauphoeta cinerea were exposed to low temperatures of 0 or 5 degrees C for various time intervals (hours to days). Development of chilling-injury (defects in crawling and uncoordinated movements) and mortality during the exposure were assessed and correlated with the changes in concentrations of metal ions (Na(+), K(+) and Mg(2+)) in the haemolymph and coxal muscle tissue. Warm-acclimated insects entered chill-coma at both low temperatures. In their haemolymph, the [Na(+)] and [Mg(2+)] linearly decreased and [K(+)] increased with the increasing time of exposure. The rate of concentration changes was higher at 0 than at 5 degrees C. The concentration changes resulted in gradually dissipating equilibrium potentials across the muscle cell membranes. For instance, E(K) decreased from -49.8 to -20.7 mV during 7 days at 5 degrees C. Such a disturbance of ion homeostasis was paralleled by the gradual development of chilling-injury and mortality. Most of the cockroaches showed chilling-injury when the molar ratio of [Na(+)]/[K(+)] in their haemolymph decreased from an initial of 4.4 to 2.1-2.5. In contrast, the cold-acclimated cockroaches did not enter chill-coma. They maintained constant concentrations of ions in their haemolymph, constant equilibrium potentials across muscle cell membranes and the development of chilling-injury was significantly suppressed at 5 degrees C for 7 days.
Adults of the bug Pyrrhocoris apterus and the beetle Alphitobius diaperinus developed chill-injury slower and survived longer when they were exposed to fluctuating thermal regimes (FTRs, where periods of low temperature were alternated with periods of higher temperature on a daily basis) rather than to constant low temperatures. The extracellular (haemolymph) concentrations of potassium ions increased with significantly higher rates in the insects exposed to constant low temperatures than in those exposed to FTRs. The concentrations of magnesium and sodium ions were maintained relatively constant or decreased slightly in both thermal regimes. The loss of body water and the increase of haemolymph osmolality contributed to, but could not fully explain, the ion concentration changes, which probably resulted also from impairing the function of an active metabolic component (ion pump) at low temperatures. This explanation was supported by observing (in P. apterus) the return toward normal [K+] during the warm "recovery" period of the FTR. Collectively, the paper stresses the importance of considering the temperature fluctuations in the experimental studies on insect cold tolerance and suggests that the positive effect of the FTR on cold tolerance may consist, at least partially, in allowing the primary ion pumping systems to re-establish the ion gradients across cell membranes and epithelia during the recovery periods at a higher temperature.
- MeSH
- draslík metabolismus MeSH
- financování organizované MeSH
- fyziologická adaptace MeSH
- hemolymfa metabolismus MeSH
- hmyz fyziologie MeSH
- hojení ran fyziologie MeSH
- homeostáza fyziologie MeSH
- nízká teplota MeSH
- osmolární koncentrace MeSH
- tělesná hmotnost MeSH
- termoregulace fyziologie MeSH
- voda metabolismus MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- MeSH
- bipolární porucha farmakoterapie patofyziologie MeSH
- blokátory kalciových kanálů farmakologie terapeutické užití MeSH
- epilepsie farmakoterapie patofyziologie MeSH
- ischemie mozku farmakoterapie patofyziologie MeSH
- lidé MeSH
- nemoci centrálního nervového systému farmakoterapie patofyziologie MeSH
- signální transdukce MeSH
- vápník fyziologie MeSH
- Check Tag
- lidé MeSH
We have developed a computer model of human cardiac ventricular myocyte (CVM), including t-tubular and cleft spaces with the aim of evaluating the impact of accumulation-depletion of ions in restricted extracellular spaces on transmembrane ion transport and ionic homeostasis in human CVM. The model was based on available data from human CVMs. Under steady state, the effect of ion concentration changes in extracellular spaces on [Ca2+]i-transient was explored as a function of critical fractions of ion transporters in t-tubular membrane (not documented for human CVM). Depletion of Ca2+ and accumulation of K+ occurring in extracellular spaces slightly affected the transmembrane Ca2+ flux, but not the action potential duration (APD90). The [Ca2+]i-transient was reduced (by 2%-9%), depending on the stimulation frequency, the rate of ion exchange between t-tubules and clefts and fractions of ion-transfer proteins in the t-tubular membrane. Under non-steady state, the responses of the model to changes of stimulation frequency were analyzed. A sudden increase of frequency (1-2.5 Hz) caused a temporal decrease of [Ca2+] in both extracellular spaces, a reduction of [Ca2+]i-transient (by 15%) and APD90 (by 13 ms). The results reveal different effects of activity-related ion concentration changes in human cardiac t-tubules (steady-state effects) and intercellular clefts (transient effects) in the modulation of membrane ion transport and Ca2+ turnover.
- MeSH
- akční potenciály MeSH
- biologické modely * MeSH
- extracelulární prostor metabolismus MeSH
- iontový transport MeSH
- ionty chemie metabolismus MeSH
- kardiomyocyty cytologie metabolismus MeSH
- lidé MeSH
- sarkolema metabolismus MeSH
- vápník metabolismus MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
