Electrophysiologic changes associated with potassium depletion of frog skin

Summary Skins from the frogRana pipiens pipiens were studied under short-circuited conditions during the course of removing and replacing potassium in the inner bathing media in 14 experiments. The intracellular potential (V _SC), fractional resistance (FR), short-circuit current (I _SC) and total tissue conductance (g _T) were constantly monitored during impalements of the epithelial cells. The mean value (±se) forV _SC was –79 (±3) mV under baseline conditions. Removal of potassium from the inner bathing solution transiently stimulated the short-circuit current and hyperpolarized the basolateral membrane; with sufficiently long incubations, the basolateral membrane was eventually depolarized. Restoration of potassium to the inner solution within 43 min after initiating the perfusion with K⁺-free solution depolarized the basolateral membrane. However, restoration of potassium after at least 11/2 hr of incubation hyperpolarized the membrane. Ouabain consistently depolarized the basolateral membrane, even after extended periods of potassium depletion as long as 320 min. In the presence of ouabain, restoration of potassium depolarized the basolateral membrane. The data provide further evidence for the concept that the Na–K exchange pump of frog skin is rheogenic. Furthermore, the results suggest that the pump continues to be active even during prolonged periods of potassium depletion, reaccumulating potassium which has leaked out of the epithelial cells.     

The interaction of n-alkanols with lipid bilayer membranes: a 2H-NMR study

The interaction of eight n-alkanols with bilayers of dimyristoylphosphatidylcholine (DMPC) has been studied by deuterium nuclear magnetic resonance (2H-NMR). At comparable temperatures and concentrations of solute in the bilayer, order parameters measured at the 1-methylene segment of the n-alkanols show a maximum for n-dodecanol. For both n-dodecanol and n-tetradecanol, orientational ordering shows a maximum at the C-4 to C-7 methylene segments, with labels at both ends of the n-alkanol exhibiting reduced order. These observations are consistent with earlier findings for n-octanol and n-decanol. Unlike the longer chain n-alkanols, ordering in n-butanol decreases from the hydroxyl group end to the methyl group end of the molecule. Orientational ordering at nine inequivalent sites in DMPC, has also been measured as a function of temperature, for bilayers containing n-butanol, n-octanol, n-dodecanol and n-tetradecanol. At the 3R,S sites on the glycerol backbone, for comparable temperatures and solute concentrations, n-butanol produces a larger disordering than the other n-alkanols. This result probably reflects the greater fraction of time spent by the hydroxyl group of n-butanol in the vicinity of the lipid polar head group compared with the hydroxyl group in longer chain n-alkanols. It was found that n-octanol orders the acyl chains of DMPC, unlike n-butanol which disorders them, and the longer chain n-alkanols which have little effect. Within experimental error, the effect of n-dodecanol on order at all sites in DMPC is the same as n-tetradecanol. The influence of n-alkanols on DMPC ordering at twelve sites has been compared with that of cholesterol which is shown to interact with DMPC bilayers in a distinctly different manner from the n-alkanols.     

A temporally stratified extension of space-for-time Cormack–Jolly–Seber for migratory animals

Understanding drivers of temporal variation in demographic parameters is a central goal of mark-recapture analysis. To estimate the survival of migrating animal populations in migration corridors, space-for-time mark–recapture models employ discrete sampling locations in space to monitor marked populations as they move past monitoring sites, rather than the standard practice of using fixed sampling points in time. Because these models focus on estimating survival over discrete spatial segments, model parameters are implicitly integrated over the temporal dimension. Furthermore, modeling the effect of time-varying covariates on model parameters is complicated by unknown passage times for individuals that are not detected at monitoring sites. To overcome these limitations, we extended the Cormack–Jolly–Seber (CJS) framework to estimate temporally stratified survival and capture probabilities by including a discretized arrival time process in a Bayesian framework. We allow for flexibility in the model form by including temporally stratified covariates and hierarchical structures. In addition, we provide tools for assessing model fit and comparing among alternative structural models for the parameters. We demonstrate our framework by fitting three competing models to estimate daily survival, capture, and arrival probabilities at four hydroelectric dams for over 200 000 individually tagged migratory juvenile salmon released into the Snake River, USA.     

Gene therapy by electroporation for the treatment of chronic renal failure in companion animals

Background  

Growth hormone-releasing hormone (GHRH) plasmid-based therapy for the treatment of chronic renal failure and its complications was examined. Companion dogs (13.1 ± 0.8 years, 29.4 ± 5.01 kg) and cats (13.2 ± 0.9 years, 8.5 ± 0.37 kg) received a single 0.4 mg or 0.1 mg species-specific plasmid injection, respectively, intramuscularly followed by electroporation, and analyzed up to 75 days post-treatment; controls underwent electroporation without plasmid administration.