Noncontact dipole effects on channel permeation. VI. 5F- and 6F-Trp gramicidin channel currents

Fluorination of peptide side chains has been shown to perturb gramicidin channel conductance without significantly changing the average side chain structure, which, it is hoped, will allow detailed analysis of electrostatic modulation of current flow. Here we report a 1312-point potassium current-voltage-concentration data set for homodimeric channels formed from gramicidin A (gA) or any of eight fluorinated Trp analogs in both lecithin and monoglyceride bilayers. We fit the data with a three-barrier, two-site, two-ion (3B2S) kinetic model. The fluorination-induced changes in the rate constants were constrained by the same factor in both lipids. The rate constant changes were converted to transition-state free-energy differences for comparison with previous electrostatic potential energy differences based on an ab initio force field. The model allowed a reasonably good fit (chi = 8.29 with 1271 degrees of freedom). The measured changes were subtle. Nevertheless, the fitted energy perturbations agree well with electrostatic predictions for five of the eight peptides. For the other three analogs, the fitted changes suggested a reduced translocation barrier rather than the reduced exit barrier as predicted by electrostatics.     

A squirrel monkey model of poststroke motor recovery

Nonhuman primate models of poststroke recovery have become increasingly rare primarily due to high purchase and maintenance costs and limited availability of nonhuman primate species. Despite this obstacle, nonhuman primate models may offer important advantages over rodent models for understanding many of the brain's mechanisms for self-repair due to greater similarity in cortical organization to humans. Since the mid-1990s, surgical, neurophysiological, and neuroanatomical methods have been developed to understand structural and functional remodeling of the cerebral cortex after an ischemic event, such as occurs in stroke. These methods require long surgical procedures and entail constant physiological monitoring. With careful attention to intraoperative and postsurgical monitoring, these procedures can be repeated multiple times in individual monkeys without untoward events. This model provides a statistically powerful approach for tracking brain plasticity in the ensuing weeks and months after a stroke-like injury, reducing the number of animals required for individual experiments. This methodology is described in detail, and many of the resulting findings that are relevant for understanding stroke recovery and the effects of rehabilitative and pharmacotherapeutic interventions are summarized.     

A cellular mechanism for prepulse inhibition

In prepulse inhibition (PPI), startle responses to sudden, unexpected stimuli are markedly attenuated if immediately preceded by a weak stimulus of almost any modality. This experimental paradigm exposes a potent inhibitory process, present in nervous systems from invertebrates to humans, that is widely considered to play an important role in reducing distraction during the processing of sensory input. The neural mechanisms mediating PPI are of considerable interest given evidence linking PPI deficits with some of the cognitive disorders of schizophrenia. Here, in the marine mollusk Tritonia diomedea, we describe a detailed cellular mechanism for PPI--a combination of presynaptic inhibition of startle afferent neurons together with distributed postsynaptic inhibition of several downstream interneuronal sites in the startle circuit.     

Growth hormone and osteoporosis: an overview of endocrinological and pharmacological insights from the Utah paradigm of skeletal physiology

Multidisciplinary advances in skeletal physiology offer a new paradigm for the effects of growth hormone (GH) and other agents on bone and osteoporosis. The still-evolving Utah paradigm of skeletal physiology supplements earlier ideas with later discovered roles of the skeleton's tissue-level 'nephron equivalents' and muscle strength in skeletal development, physiology and disorders. This article summarizes how these factors could influence the effects of GH on bone strength and bone 'mass', and the use of GH in the treatment of osteoporoses. Although the cellular and molecular biological mechanisms involved remain obscure, the associated cascades of cellular, genetic and biochemical processes and molecules should offer many opportunities to find or design agents that have medically useful effects on bone and muscle without giving rise to unwanted side-effects.     

Why the ISMNI and the Utah paradigm? Their role in skeletal and extraskeletal disorders

Besides bringing problems, aging can let the mind's eye see more clearly than before, and it can let us express ourselves better. As age, experience and common sense examine today's skeletal medicine and surgery two questions keep popping up: A) How did we fail?; B) How to make it better? The Utah paradigm of skeletal physiology and the seminal ISMNI offer some answers, but exploiting them faces problems. Problem #1: By 1960 all clinicians and physiologists 'knew' (as the ancients 'knew' this world is flat) that effector cells controlled solely by nonmechanical agents explain all skeletal physiology and disorders ('effector cells' include osteoblasts, osteoclasts, chondroblasts and fibro-blasts). Or, nonmechanical agents -->cell level -->organ and intact subject. Adding later-discovered information to that 1960 view led to the Utah paradigm, which reveals the formerly hidden tissue-level 'dimension' of skeletal physiology. It builds on this idea: (mechanical + nonmechanical agents) -->(tissue level + cell level) --> organ and intact subject. The paradigm assigns great influence of neuromuscular physiology and physical activities on skeletal architecture, strength and mechanical competence. It also exposes flaws in many older views so controversies arise. Problem #2: The Utah paradigm and Wegner's concept of plate tectonics in geology seem alike in that each is valid but came before its time, so others fought it. They differ in this: The fight about Wegner's idea is over, but for the Utah paradigm and the ISMNI it just began. Hence more controversies. Nevertheless: A growing minority realizes that paradigm provides a far better base to build on than its antecedents, and since it keeps evolving as more evidence comes in it could endure for some decades. Yet very few realize this: It and the ISMNI have important implications for fields besides biomechanics and orthopaedics. Examples include anatomy, cardiovascular disease, dentistry, endocrinology, family medicine, gastroenterology, general surgery, genetics, gerontology, gynecology, maxillofacial surgery, neurology, neurosurgery, nutrition, ophthalmology, pathology, pediatrics, physical medicine and rehabilitation, plastic surgery, radiology, rheumatology, space and sports medicine, and urology. Quite a list! For the italicized questions above this article offers answers, of which its conclusion distills an essence.     

Expression of beta-defensin-1 in chimpanzee (Pan troglodytes) airways

In human airways, beta-defensins function in the elimination of various pathogens. They have been identified in a wide range of species. Here we report the identification and expression of chimpanzee beta-defensin-1 (cBD1), which is a homolog of human beta-defensin-1, in chimpanzee airways and skin. The cBD1 cDNA sequence differs by only one synonymous nucleotide substitution compared to the human cDNA sequence. In situ hybridization revealed that in lung tissue beside alveolar macrophages also airway epithelial cells, endothelial cells and type II pneumocytes express cBD1 mRNA. In skin, cBD1 mRNA was expressed in keratinocytes and endothelial cells. Together, these results show similarity in structure and expression pattern and perhaps in function.     

Genetic Analysis of the Role of the Transfer Gene, traN, of the F and R100-1 Plasmids in Mating Pair Stabilization during Conjugation

Mating pair stabilization occurs during conjugative DNA transfer whereby the donor and recipient cells form a tight junction which requires pili as well as TraN and TraG in the donor cell. The role of the outer membrane protein, TraN, during conjugative transfer was examined by introduction of a chloramphenicol resistance cassette into the traN gene on an F plasmid derivative, pOX38, to produce pOX38N1::CAT. pOX38N1::CAT was greatly reduced in its ability to transfer DNA, indicating that TraN plays a greater role in conjugation than previously thought. F and R100-1 traN were capable of complementing pOX38N1::CAT transfer equally well when wild-type recipients were used. F traN, but not R100-1 traN, supported a much lower level of transfer when there was an ompA mutation or lipopolysaccharide (LPS) deficiency in the recipient cell, suggesting receptor specificity. The R100-1 traN gene was sequenced, and the gene product was found to exhibit 82.3% overall similarity with F TraN. The differences were mainly located within a central region of the proteins (amino acids 162 to 333 of F and 162 to 348 of R100-1). Deletion analysis of F traN suggested that this central portion might be responsible for the receptor specificity displayed by TraN. TraN was not responsible for TraT-dependent surface exclusion. Thus, TraN, and not the F pilus, appears to interact with OmpA and LPS moieties during conjugation, resulting in mating pair stabilization, the first step in efficient mobilization of DNA.     

On the 13C/12C isotopic signal of day and night respiration at the mesocosm level

While there is currently intense effort to examine the ¹³C signal of CO₂ evolved in the dark, less is known on the isotope composition of day‐respired CO₂. This lack of knowledge stems from technical difficulties to measure the pure respiratory isotopic signal: day respiration is mixed up with photorespiration, and there is no obvious way to separate photosynthetic fractionation (pure c_i/c_a effect) from respiratory effect (production of CO₂ with a different δ¹³C value from that of net‐fixed CO₂) at the ecosystem level. Here, we took advantage of new simple equations, and applied them to sunflower canopies grown under low and high [CO₂]. We show that whole mesocosm‐respired CO₂ is slightly ¹³C depleted in the light at the mesocosm level (by 0.2–0.8‰), while it is slightly ¹³C enriched in darkness (by 1.5–3.2‰). The turnover of the respiratory carbon pool after labelling appears similar in the light and in the dark, and accordingly, a hierarchical clustering analysis shows a close correlation between the ¹³C abundance in day‐ and night‐evolved CO₂. We conclude that the carbon source for respiration is similar in the dark and in the light, but the metabolic pathways associated with CO₂ production may change, thereby explaining the different ¹²C/¹³C respiratory fractionations in the light and in the dark.