A century of (epithelial) transport physiology: from vitalism to molecular cloning

Cellular sentience as the primary source of biological order and evolution

All life is cellular, starting some 4 billion years ago with the emergence of the first cells. In order to survive their early evolution in the face of an extremely challenging environment, the very first cells invented cellular sentience and cognition, allowing them to make relevant decisions to survive through creative adaptations in a continuously running evolutionary narrative. We propose that the success of cellular life has crucially depended on a biological version of Maxwell's demons which permits the extraction of relevant sensory information and energy from the cellular environment, allowing cells to sustain anti-entropic actions. These sensor-effector actions allowed for the creative construction of biological order in the form of diverse organic macromolecules, including crucial polymers such as DNA, RNA, and cytoskeleton. Ordered biopolymers store analogue (structures as templates) and digital (nucleotide sequences of DNA and RNA) information that functioned as a form memory to support the development of organisms and their evolution. Crucially, all cells are formed by the division of previous cells, and their plasma membranes are physically and informationally continuous across evolution since the beginning of cellular life. It is argued that life is supported through life-specific principles which support cellular sentience, distinguishing life from non-life. Biological order, together with cellular cognition and sentience, allow the creative evolution of all living organisms as the authentic authors of evolutionary novelty.

Differentially expressed genes in cotyledon of ewes fed mycotoxins

BACKGROUND

Ergot alkaloids (E+) are mycotoxins produced by the endophytic fungus, Epichloë coenophiala, in tall fescue that are associated with ergotism in animals. Exposure to ergot alkaloids during gestation reduces fetal weight and placental mass in sheep. These reductions are related to vasoconstrictive effects of ergot alkaloids and potential alterations in nutrient transport to the fetus. Cotyledon samples were obtained from eight ewes that were fed E+ (n = 4; E+/E+) or E- (endophyte-free without ergot alkaloids; n = 4; E-/E-) seed during both mid (d 35 to 85) and late (d 85-133) gestation to assess differentially expressed genes associated with ergot alkaloid induced reductions in placental mass and fetal weight, and discover potential adaptive mechanisms to alter nutrient supply to fetus.

RESULTS

Ewes fed E+/E+ fescue seed during both mid and late gestation had 20% reduction in fetal body weight and 33% reduction in cotyledon mass compared to controls (E-/E-). Over 13,000 genes were identified with 110 upregulated and 33 downregulated. Four genes had a |log2FC| > 5 for ewes consuming E+/E+ treatment compared to controls: LECT2, SLC22A9, APOC3, and MBL2. REViGO revealed clusters of upregulated genes associated glucose, carbohydrates, lipid, protein, macromolecular and cellular metabolism, regulation of wound healing and response to starvation. For downregulated genes, no clusters were present, but all enriched GO terms were associated with anion and monocarboxylic acid transport. The complement and coagulation cascade and the peroxisome proliferator-activated receptor signaling pathway were found to be enriched for ewes consuming E+/E+ treatment.

CONCLUSIONS

Consumption of ergot alkaloids during gestation altered the cotyledonary transcriptome specifically related to macronutrient metabolism, wound healing and starvation. These results show that ergot alkaloid exposure upregulates genes involved in nutrient metabolism to supply the fetus with additional substrates in attempts to rescue fetal growth.

Reproductive state and water deprivation increase plasma corticosterone in a capital breeder

Plasma corticosterone (CORT) concentrations fluctuate in response to homeostatic demands. CORT is widely recognized as an important hormone related to energy balance. However, far less attention has been given to the potential role of CORT in regulating salt and water balance or responding to osmotic imbalances. We examined the effects of reproductive and hydric states on CORT levels in breeding Children's pythons (Antaresia childreni), a species with substantial energetic and hydric costs associated with egg development. Using a 2 × 2 experimental design, we examined how reproduction and water deprivation, both separately and combined, impact CORT levels and how these changes correlate with hydration (plasma osmolality) and energy levels (blood glucose). We found that reproduction leads to increased CORT levels, as does dehydration induced by water deprivation. The combined impact of reproduction and water deprivation led to the largest increases in CORT levels. Additionally, we found significant positive relationships among CORT levels, plasma osmolality, and blood glucose. Our results provide evidence that both reproductive activity and increased plasma osmolality can lead to increased plasma CORT in an ectotherm, which could be explained by either CORT having a role as a mineralocorticoid or CORT being elevated as part of a stress response to resource imbalances.

Amino Acids in Reproductive Nutrition and Health

Amino acids are not only the building blocks of proteins, an indispensable component of cells, but also play versatile roles in regulating cell metabolism, proliferation, differentiation and growth by themselves or through their derivatives. At the whole body level, the bioavailability and metabolism of amino acids, interacting with other macronutrients, is critical for the physiological processes of reproduction including gametogenesis, fertilization, implantation, placentation, fetal growth and development. In fertilization and early pregnancy, histotroph in oviductal and uterine secretions provides nutrients and microenvironment for conceptus (embryo and extraembryonic membranes) development. These nutrients include select amino acids in histotroph (arginine, leucine and glutamine of particular interest) that stimulate conceptus growth and development, as well as interactions between maternal uterus and the conceptus, thus impacting maintenance of pregnancy, placental growth, development and functions, fetal growth and development, and consequential pregnancy outcomes. Gestational protein undernutrition causes fetal growth restriction and predisposes cardiovascular, metabolic diseases and others in offspring via multiple mechanisms, whereas the supplementation of glycine, leucine and taurine during pregnancy partially rescues growth restriction and beneficially modulates fetal programming. Thus, amino acids are essential for the fertility of humans and all animals.

The early modern kidney--nephrology in and about the nineteenth century (part 2)

Two basic science specialties that matured in the nineteenth century were instrumental in the transformation of medicine into a scientific discipline and in the process of establishing the evidentiary basis of the fundamental role of the kidney in maintaining homeostasis, whose continued exploration would lead to the emergence of nephrology in the following century. The first specialty was that of chemistry, which progressed from a descriptive to an analytical, organic, biological, and physical science that progressively eroded the animism of the "vital" forces of old and replaced it with the physicochemical forces and laws of chemical reactions that govern the "matters of life". The second specialty was that of cell biology, which established the cell as the structural and functional unit of living organisms, be they plant or animal. Refined microscopic technologies then helped to identify the structural components of the cell, amongst which the plasma membrane emerged as the most important in regulating the separation of the intracellular machinery from its external environment and thereby maintaining the internal milieu of cells. The interaction of these two specialties (chemistry, cell biology) clarified the functions of the cell in health and disease and extended it to the study of epithelial cell transport. This transforming turn of events established the role of the renal tubules in the vital function of the kidney of maintaining body homeostasis, a function well beyond that of the passive excretory filter of wastes and excess fluids it had been considered theretofore.

Biophysical model of ion transport across human respiratory epithelia allows quantification of ion permeabilities

Lung health and normal mucus clearance depend on adequate hydration of airway surfaces. Because transepithelial osmotic gradients drive water flows, sufficient hydration of the airway surface liquid depends on a balance between ion secretion and absorption by respiratory epithelia. In vitro experiments using cultures of primary human nasal epithelia and human bronchial epithelia have established many of the biophysical processes involved in airway surface liquid homeostasis. Most experimental studies, however, have focused on the apical membrane, despite the fact that ion transport across respiratory epithelia involves both cellular and paracellular pathways. In fact, the ion permeabilities of the basolateral membrane and paracellular pathway remain largely unknown. Here we use a biophysical model for water and ion transport to quantify ion permeabilities of all pathways (apical, basolateral, paracellular) in human nasal epithelia cultures using experimental (Ussing Chamber and microelectrode) data reported in the literature. We derive analytical formulas for the steady-state short-circuit current and membrane potential, which are for polarized epithelia the equivalent of the Goldman-Hodgkin-Katz equation for single isolated cells. These relations allow parameter estimation to be performed efficiently. By providing a method to quantify all the ion permeabilities of respiratory epithelia, the model may aid us in understanding the physiology that regulates normal airway surface hydration.

Reduced dynamic models in epithelial transport

Most models developed to represent transport across epithelia assume that the cell interior constitutes a homogeneous compartment, characterized by a single concentration value of the transported species. This conception differs significantly from the current view, in which the cellular compartment is regarded as a highly crowded media of marked structural heterogeneity. Can the finding of relatively simple dynamic properties of transport processes in epithelia be compatible with this complex structural conception of the cell interior? The purpose of this work is to contribute with one simple theoretical approach to answer this question. For this, the techniques of model reduction are utilized to obtain a two-state reduced model from more complex linear models of transcellular transport with a larger number of intermediate states. In these complex models, each state corresponds to the solute concentration in an intermediate intracellular compartment. In addition, the numerical studies reveal that it is possible to approximate a general two-state model under conditions where strict reduction of the complex models cannot be performed. These results contribute with arguments to reconcile the current conception of the cell interior as a highly complex medium with the finding of relatively simple dynamic properties of transport across epithelial cells.

The plasma membrane potential and the organization of the actin cytoskeleton of epithelial cells

The establishment and maintenance of the polarized epithelial phenotype require a characteristic organization of the cytoskeletal components. There are many cellular effectors involved in the regulation of the cytoskeleton of epithelial cells. Recently, modifications in the plasma membrane potential (PMP) have been suggested to participate in the modulation of the cytoskeletal organization of epithelia. Here, we review evidence showing that changes in the PMP of diverse epithelial cells promote characteristic modifications in the cytoskeletal organization, with a focus on the actin cytoskeleton. The molecular paths mediating these effects may include voltage-sensitive integral membrane proteins and/or peripheral proteins sensitive to surface potentials. The voltage dependence of the cytoskeletal organization seems to have implications in several physiological processes, including epithelial wound healing and apoptosis.

Cystic fibrosis transmembrane conductance regulator modulators for personalized drug treatment of cystic fibrosis: progress to date

This article considers the issue of personalized drug discovery for the orphan disease cystic fibrosis (CF) to deliver a candidate for therapeutic development. CF is a very complicated disease due to numerous anomalies of the gene leading to progressive severity and morbidity. Despite extensive research efforts, 20 years after the cloning of the CF gene, CF patients are still waiting for a curative treatment as prescribed medications still target the secondary manifestations of the disease rather than the gene or the CF transmembrane conductance regulator (CFTR) protein. New therapeutics aimed at improving mutant CFTR functions, also known as 'protein repair therapy' are nevertheless hoped and predicted to replace some of the currently used therapy, while improving the quality of life as well as life expectancy of CF patients. Although there is substantial variability in the cost of treating CF between countries, a protein repair therapy should also alleviate the financial burden of medical costs for CF patients and their families. Finding new drugs or rediscovering old ones for CF is critically dependent on the delivery of molecular and structural information on the CFTR protein, on its mutated version and on the network of CFTR-interacting proteins. The expertise needed to turn compounds into marketable drugs for CF will depend on our ability to provide biological information obtained from pertinent models of the disease and on our success in transferring safe molecules to clinical trials. Predicting a drug-induced response is also an attractive challenge that could be rapidly applied to patients.

HCO (3)(-) secretion and CaCO3 precipitation play major roles in intestinal water absorption in marine teleost fish in vivo

The intestine of marine teleosts must effectively absorb fluid from ingested seawater to avoid dehydration. This fluid transport has been almost exclusively characterized as driven by NaCl absorption. However, an additional feature of the osmoregulatory role of the intestine is substantial net HCO(3)(-) secretion. This is suggested to drive additional fluid absorption directly (via Cl(-)/HCO(3)(-) exchange) and indirectly by precipitating ingested Ca(2+) as CaCO(3), thus creating the osmotic gradient for additional fluid absorption. The present study tested this hypothesis by perfusing the intestine of the European flounder in vivo with varying [Ca(2+)]: 10 (control), 40, and 90 mM. Fractional fluid absorption increased from 47% (control) to 73% (90 mM Ca(2+)), where almost all secreted HCO(3)(-) was excreted as CaCO(3). This additional fluid absorption could not be explained by NaCl cotransport. Instead, a significant positive relationship between Na(+)-independent fluid absorption and total HCO(3)(-) secretion was consistent with the predicted roles for anion exchange and CaCO(3) precipitation. Further analysis suggested that Na(+)-independent fluid absorption could be accounted for by net Cl(-) and H(+) absorption (from Cl(-)/HCO(3)(-) exchange and CO(2) hydration, respectively). There was no evidence to suggest that CaCO(3) alone was responsible for driving fluid absorption. However, by preventing the accumulation of luminal Ca(2+) it played a vital role by dynamically maintaining a favorable osmotic gradient all along the intestine, which permits substantially higher rates of solute-linked fluid absorption. To overcome the resulting hyperosmotic and highly acidic absorbate, it is proposed that plasma HCO(3)(-) buffers the absorbed H(+) (from HCO(3)(-) production), and consequently reduces the osmolarity of the absorbed fluid entering the body.

The intestinal guanylin system and seawater adaptation in eels

Guanylin and uroguanylin are principal intestinal hormones secreted into the lumen to regulate ion and water absorption via a specific receptor, guanylyl cyclase-C (GC-C). As the intestine is an essential organ for seawater (SW) adaptation in teleost fishes, the intestinal guanylin system may play a critical role in SW adaptation. Molecular biological studies identified multiple guanylins (guanylin, uroguanylin and renoguanylin) and their receptors (GC-C1 and GC-C2) in eels. The relative potency of the three ligands on cGMP production in transiently expressed receptors was uroguanylin > guanylin >or= renoguanylin for CG-C1 and guanylin >or= renoguanylin > uroguanylin for GC-C2. Eel guanylin and GC-C genes are expressed exclusively in the intestine and kidney, and the level of expression is greater in SW eels than in freshwater (FW) eels except for renoguanylin. Physiological studies using Ussing chambers showed that the middle and posterior intestine are major sites of action of guanylins, where they act on the mucosal side to decrease short circuit current (I(sc)) in a dose-dependent manner. The ID(50) of guanylins for transport inhibition was 50-fold greater than that of atrial natriuretic peptide that acts from the serosal side as an endocrine hormone. However, only guanylins reversed I(sc) to levels below zero. Pharmacological analyses using various blockers showed that among transporters and channels localized on the intestinal cells of SW teleost fish, the cystic fibrosis transmembrane conductance regulator Cl(-) channel (CFTR) on the apical membrane is the major target of guanylins. Collectively, guanylins are synthesized locally in the intestine and secreted into the lumen to act on the GC-Cs in the apical membrane of eel intestinal cells. Then, intracellular cGMP production after ligand-receptor interaction activates CFTR and probably induces Cl(-) and/or HCO3- secretion into the lumen as suggested in mammals. The physiological significance of the anion secretion induced by the luminal guanylin/GC-C system on SW adaptation may rival or exceed that of the serosally derived natriuretic peptides in the euryhaline eel.

GSK3β inhibition and KATP channel opening mediate acute opioid-induced cardioprotection at reperfusion

Both glycogen synthase kinase 3beta (GSK3beta) and the ATP-dependant potassium channel (K(ATP)) mediate opioid-induced cardioprotection (OIC). However, whether direct K(ATP) channel openers induce cardioprotection prior to reperfusion and their signaling cascade position with respect to GSK3beta inhibition is unknown. Therefore, we investigated the role of K(ATP) channel opening at reperfusion in OIC, and the interaction between the GSK signaling axis and K(ATP) channels in cardioprotection.Male Sprague-Dawley rats underwent 30 minutes ischemia with 2 hours of reperfusion and infarct size was determined. Rats given the nonselective opioid agonist, morphine (0.3 mg/kg), or the selective delta opioid agonist, BW373U86 (1.0 mg/kg), 5 minutes prior to reperfusion reduced infarct size (40.3+/-1.6*, 39.7+/-1.9* versus 60.0+/-1.1%, respectively, * P<0.001%). This protection was abrogated with prior administration of the putative sarcolemmal K(ATP) antagonist, HMR-1098 (6 mg/kg), or the putative mitochondrial K(ATP) antagonist, 5-HD (10 mg/kg). The putative sK(ATP) channel opener, P-1075 (1microg/kg) or the putative mK(ATP) channel opener, BMS-191095 (1 mg/kg) given 5 minutes prior to reperfusion also reduced infarct size (41.8+/-2.4*, 43.4+/-1.4*) and protection was abrogated by prior administration of the PI3k inhibitor wortmannin (60.0+/-1.7, 64.0+/-2.6%, respectively, * P<0.001). Cardioprotection afforded by the GSK inhibitor SB216763 (0.6 mg/kg) given 5 minutes prior to reperfusion was also partially blocked by either HMR or 5-HD and completely blocked when HMR and 5-HD were given in combination (40.8+/-1.6*, 50.4+/-1.6;; 49.4+/-1.7;, 61.6+/-1.6%, respectively, * or ; P<0.001). These data indicate that both the sK(ATP) and mK(ATP) channel are involved in acute OIC and the GSK signaling axis regulates cardioprotection via K(ATP) channel opening.

Mechanism by which activation of delta-opioid receptor reduces the severity of postresuscitation myocardial dysfunction

OBJECTIVE

Postresuscitation myocardial dysfunction has been recognized as a leading cause of early death after initially successful cardiopulmonary resuscitation. We have previously demonstrated that opening adenosine triphosphate (ATP)-sensitive K (KATP) channels or activation of delta-opioid receptors minimized the severity of postresuscitation myocardial dysfunction and increased the duration of postresuscitation survival. In the present study, we investigated the potential mechanism of myocardial protection following delta-opioid receptor activation in a rat model of cardiac arrest and cardiopulmonary resuscitation.

DESIGN

Randomized prospective animal study.

SETTING

Animal research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Ventricular fibrillation was induced in 24 Sprague-Dawley rats. Mechanical ventilation and precordial compression were initiated after 8 mins of untreated ventricular fibrillation. Defibrillation was attempted after 6 mins of cardiopulmonary resuscitation. The animals were randomized to four groups: a) pentazocine (0.3 mg/kg), a delta-opioid receptor agonist; b) pentazocine pretreated with KATP channel blocker, glibenclamide (0.3 mg/kg), administered 45 mins before induction of ventricular fibrillation; c) glibenclamide pretreated alone 45 mins before induction of ventricular fibrillation; and d) placebo. Pentazocine or saline placebo was injected into the right atrium after 5 mins of untreated ventricular fibrillation.

MEASUREMENTS AND MAIN RESULTS

Postresuscitation myocardial function, as measured by the rate of left ventricular pressure increase at 40 mm Hg, left ventricular end-diastolic pressure, and cardiac index, was significantly improved in pentazocine-treated animals. This was associated with significantly prolonged duration of survival. Except for ease of defibrillation, the beneficial effects of pentazocine were abolished by pretreatment with the KATP channel blocker glibenclamide.

CONCLUSIONS

The postresuscitation myocardial protective effects provided by activation of delta-opioid receptor may be mediated via opening KATP channels.

Kidney function in mice lacking aldosterone

To explore the effects of decreased amounts or absence of aldosterone, we have disrupted the gene coding for aldosterone synthase (AS) in mice and investigated blood pressure and kidney function in AS+/+, AS+/-, and AS-/- mice. AS+/- mice have normal blood pressures and show no abnormalities in electrolytes or kidney gene expression, but they have significantly higher than normal urine volume and lower urine osmolality. In contrast, the AS-/- mice have low blood pressure, abnormal electrolyte homeostasis (increased plasma concentrations of K+, Ca2+, and Mg2+ and decreased concentrations of HCO3(-) and Cl- but no difference in the plasma Na+ level), and disturbances in water metabolism (higher urine output, decreased urine osmolality, and impaired urine concentrating and diluting ability). Absence of aldosterone in the AS-/- mice induced several compensatory changes: an increased food intake-to-body weight ratio, an elevated plasma concentration of glucocorticoids, and strong activation of the renin-angiotensin system. Parallel with the markedly increased synthesis and release of renin, the AS-/- mice showed increased expression of cyclooxygenase-2 (COX-2) in macula densa. On salt supplementation, plasma electrolyte concentrations and kidney renin and COX-2 levels became similar to those of wild-type mice, but the lower blood pressure of the AS-/- mice was not corrected. Thus absence of aldosterone in AS-/- mice results in impairment of Na+ reabsorption in the distal nephron, decreased blood pressure, and strong renin-angiotensin system activation. Our data show the substantial correction of these abnormalities, except the low blood pressure, by high dietary salt does not depend on aldosterone.

The effects of the delta-opioid agonist SNC80 on hind-limb motor function and neuronal injury after spinal cord ischemia in rats

Recent investigation suggested neuroprotective efficacy of a delta-opioid agonist in the brain. We investigated the effects of intrathecal treatment with a delta-opioid agonist (SNC80) on spinal cord ischemia (SCI) in rats. SCI was induced with an intraaortic balloon catheter. The animals were randomly allocated to one of the following five groups: 1) SNC80 before 9 min of SCI (SNC-9; n = 12), 2) vehicle before 9 min of SCI (V-9; n = 12), 3) SNC80 before 11 min of SCI (SNC-11; n = 10), 4) vehicle before 11 min of SCI (V-11; n = 12), or 5) sham (n = 12). SNC80 (400 nmol) or vehicle was administered 15 min before SCI. Forty-eight hours after reperfusion, hind-limb motor function was assessed by using the Basso, Beattie, Bresnahan (BBB) scale (0 = paraplegia; 21 = normal) and histological assessment of the L4 and L5 spinal segments was performed. BBB scores in the SNC-9 group were higher compared with those in the V-9 group (P < 0.05), whereas there were no differences in BBB scores between the SNC-11 and V-11 groups. There were significantly more normal neurons in the SNC-9 and SNC-11 groups than in the V-9 and V-11 groups (P < 0.05). The results indicate that intrathecal treatment with the delta-opioid agonist SNC80 can attenuate hind-limb motor dysfunction and neuronal injury after SCI in rats.

Effect of exogenous kappa-opioid receptor activation in rat model of myocardial infarction

The involvement of opioid receptor activation during ischemia-reperfusion is somewhat controversial. While it is generally accepted that activation of the delta-opioid receptor (DOR) is cardioprotective, and may indeed be an important mediator of ischemic preconditioning, the role of the kappa-opioid receptor (KOR) is less well understood. To this end, we examined three different KOR agonists and their effects upon infarct size and arrhythmia development. Male Sprague-Dawley rats were subjected to 30 minutes of occlusion followed by 90 minutes of reperfusion. Opioid receptor agonists were administered 10 minutes before the onset of ischemia, while the opioid antagonists were given 20 minutes before occlusion. Untreated rats exhibited an infarct size (IS/AAR%) of 52.4 +/- 2.7%. Pretreatment with the DOR agonist, BW373U86, limited infarct development to 37.2 +/- 1.8%, which was reversed by the selective DOR antagonist, BNTX. All three KOR agonists studied, U50,488, ICI 204,448, and BRL 52537 significantly reduced infarct size to levels comparable to that of BW373U86. The infarct-sparing effects of U50,488 and ICI 204,448 were abolished by the selective KOR antagonist, nor-BNI. Nor-BNI failed to inhibit the cardioprotective effects of BRL 52537. Furthermore, U50,488 and BRL 52537, but not ICI 204,448, significantly reduced the incidence of arrhythmias. These effects were not blocked by nor-BNI. These data demonstrate that KOR activation provides a similar degree of infarct size reduction as DOR activation. KOR agonists also reduced arrhythmogenesis; however, these responses appear to be independent of KOR activation.

Effect of a delta receptor agonist on duration of survival during hemorrhagic shock

OBJECTIVES

Selective delta receptor agonists have been shown to stabilize membrane physiologic processes, reduce metabolic rates, and provide protection against ischemic insults through K(ATP) channel opening in a variety of organ beds. However, their potential for affecting outcomes in states of generalized ischemia has not been explored. The authors examined the effect of the nonselective delta receptor agonist, DADLE (D-Ala2-Leu5-enkephalin), on hemodynamic stability and duration of survival in an animal model of severe hemorrhagic shock.

METHODS

Conscious Sprague Dawley rats with indwelling catheters were hemorrhaged at a rate of 3.25 mL/100 grams over 20 minutes after half of the group received 1% DADLE (1 mg/kg IV). Following the hemorrhage, all rats were continuously monitored for heart rate (HR), mean arterial pressure (MAP), and life signs for up to three hours (death defined as apnea, systolic blood pressure < 30 mm Hg without pulsations, and electroencephalographic silence). Survival rates and hemodynamic trends were compared between the control and DADLE-treated groups.

RESULTS

In the 14 rats studied (8 DADLE; 6 controls), initial hemorrhage resulted in similar hemodynamic shock (average MAP fall: 118 to 59 vs 119 to 55 mm Hg). Analysis of survival at 3.5 hours revealed statistically significant differences between the control and DADLE groups. While 50% of the DADLE group survived past the three hours, no control animals were still alive at the end of the experimental period. The MAP trended downward and the HR increased for the control group, but all hemodynamic parameters stabilized in the rats treated with DADLE.

CONCLUSIONS

Most current strategies for treating shock focus on the supply side of resuscitation. The coordinated various actions of DADLE have the potential to work in concert in the intact organism to improve overall survival during severe hemorrhagic shock. In an animal model of severe hemorrhagic shock, there was improvement in hemodynamic stability and a prolonged survival with DADLE treatment. Physiologic manipulation with DADLE appears to be a way to improve survival during shock with possible clinical implications.

SNC-80-induced preconditioning: selective activation of the mitochondrial adenosine triphosphate-gated potassium channel

Pharmacologic preconditioning by delta-opioid agonists occurs via activation of an adenosine triphosphate (ATP)-gated potassium channel (I(KATP)). Opening of mitochondrial I(KATP) confers pharmacologic preconditioning whereas opening the sarcolemmal I(KATP) shortens action potential duration and is proarrhythmic. This study investigated whether SNC-80, a selective delta-opioid agonist, is associated with development of ventricular arrhythmia due to activation of I(KATP). Rabbit isolated hearts were subjected to 12 min of hypoxia and 40 min of reoxygenation after pretreatment with SNC-80 (1 microM, n = 6), pinacidil (1.25 microM, n = 12), or BMS-191095 (6.0 microM, n = 4). Nine additional hearts served as controls. The cytoprotective effects of SNC-80 at a concentration of 1 microM were confirmed using 30 min of regional ischemia followed by 120 min of reperfusion. Ventricular fibrillation (VF) developed in 11 of 12 pinacidil-treated hearts whereas none of the SNC-80-treated (zero of six) hearts developed VF (P < 0.001 compared with pinacidil pretreatment) and zero of four BMS-191095-pretreated hearts developed VF. Similarly, zero of nine control hearts developed VF. SNC-80 reduced infarct size expressed as a percentage of the area at risk from 33 +/- 4% to 14 +/- 3% (P = 0.004) compared with control. SNC-80, which selectively activates the delta-opioid receptor, provided cytoprotection but did not induce VF after hypoxia reoxygenation. The results indicate that pinacidil-induced nonselective activation of I(KATP) results in proarrhythmia that is dependent on activation of the sarcolemmal I(KATP). Selectivity for the mitochondrial I(KATP) is necessary to prevent induction of a proarrhythmic state.

General models for water transport across leaky epithelia

The group of leaky epithelia, such as proximal tubule and small intestine, have several common properties in regard to salt and water transport. The fluid transport is isotonic, the transport rate increases in dilute solutions, and water can be transported uphill. Yet, it is difficult to find common features that could form the basis for a general transport model. The direction of transepithelial water transport does not correlate with the direction of the primary active Na+ transport, or with the ultrastucture as defined by the location of apical and basolateral membranes, of the junctional complex and the lateral intercellular spaces. The presence of specific water channels, aquaporins, increases the water permeability of the epithelial cell membranes, i.e., the kidney proximal tubule. Yet other leaky epithelia, for example, the retinal pigment epithelium, have no known aquaporins. There is, however, a general correlation between the direction of transepithelial transport and the direction of transport via cotransporters of the symport type. A simple epithelial model based on water permeabilities, a hyperosmolar compartment and restricted salt diffusion, is unable to explain epithelial transport phenomena, in particular the ability for uphill water transport. The inclusion of cotransporters as molecular water pumps in these models alleviates this problem.

The blockade of mineralocorticoid hormone signaling provokes dramatic teratogenesis in cultured rat embryos

Although the administration of adrenocortical hormones to pregnant rats provokes only limited effect on the growth and development of the fetus, the direct influence of these steroids on cultured embryos has never been studied. The disruption of cell signaling by ZK 91587, which specifically occupies the mineralocorticoid receptor, resulted within 2 days in significant and pronounced adverse effects on the total length, the somite number, the embryo curvature, the communication between vitelline and umbilical blood vessels in the allantoid, and the vascularization of the vitelline sac, in 244-hour Wistar rat embryos in culture. The average score of 16 organs declined in a dose-dependent manner, following exposure to ZK 91587, and this was totally reversed by 10 microM aldosterone which, by itself, did not at all influence the embryonic development. The organogenesis was inhibited in the order: hind limb > fore limb > optic stalk > brain > olfactory pit > otic vesicle. ZK 91587 was completely ineffective in embryos that had attained the age of 260 hours. Similar, but less dramatic, results were obtained with the mineralocorticoid antagonist RU 26752, and with the antiglucocorticoid RU 38486. Sprague-Dawley rat embryos responded in a manner similar to the Wistar conceptuses. Thus, steroid receptor-mediated cell signaling is of critical importance to the growth and development of cultured rat embryos, which form a new model system to unravel adrenocortical hormone action.

Cardioprotection: emerging pharmacotherapy

By the year 2020, it is predicted that acute coronary occlusion will be the major cause of death in the world. Recent advances in reperfusion therapy have substantially improved survival of patients with acute coronary syndromes. While early reperfusion reduces mortality, a time limitation exists with regard to myocardial salvage. In fact, the major limiting factor in further improving survival of patients with myocardial ischaemia is the susceptibility of the cardiomyocyte to ischaemic insult and lethal cell injury. Over the last decade substantial progress has been made in our understanding of the fundamental mechanisms of ischaemia/reperfusion injury. From this work novel means which limit or delay myocyte death have emerged and are currently under development as therapeutic candidates for the management of acute coronary syndromes. This report examines cardioprotective mechanisms and reviews clinical evidence for myocardial protective therapies.

Mineralocorticoid receptor-mediated signaling regulates the ion gated sodium channel in vascular endothelial cells and requires an intact cytoskeleton

The PCR analysis followed by sequence alignment showed that both the mineralocorticoid receptor (MCR) and the epithelial sodium channel (ENaC) genes were expressed in the human vascular endothelial cell line (ECV). The growth and multiplication of the ECV in culture were influenced by both aldosterone and the MCR-specific antagonist ZK 91587. Following double labelled immunofluorescence recorded by confocal microscopy, both the MCR and the ENaC were found to colocalize with the tubulin filaments in ECV cells in situ; no association was observed with cellular actin. ZK 91587 not only eliminated the basal expression, but it also impaired the transactivation of the ENaC gene by aldosterone. The disruption of actin and tubulin by cytochalasin D and colchicine, respectively, resulted in the total elimination of ENaC induction by aldosterone. These studies suggest that (i) the transcriptional regulation of the ENaC gene by the MCR-mediated signalling is not restricted to epithelial cells and requires cytoskeleton integrity in ECV cells in situ, (ii) tubulin may form a new and novel mediator in cell regulation, and (iii) the vascular tone may actually be regulated via transactivation of the ion gated sodium channel in the endothelial cell of the blood vessels under direct, receptor-mediated action of aldosterone.

Epithelial sodium channel and the mineralocorticoid receptor in cultured rat Müller glial cells

Müller glial cells are the major non-neuronal cells of the retina. They are involved in retinal function and exert a profound influence on the function of retinal neurons. We present an in vitro study of the localization of the mineralocorticoid receptor (MCR) and of the epithelial sodium channel (ENaC) in rat Müller glial cells isolated from rat retina, using respectively, a polyclonal antiserum raised against the rat purified MCR, and a rabbit polyclonal antibody against the 14-amino acid (aa) peptide QGLGKGDKREEQGL, which corresponds to the N-terminal region (44-58aa) of the alpha-subunit of the ENaC. In an immunocytochemical study using anti-MCR and anti-ENaC antibodies, the MCR was detected as a protein present in the cytoplasm and in the nucleus, whereas ENaC was detected as a membrane-bound protein. Reverse transcription-polymerase chain reaction (RT-PCR) analysis using specific primers, 5'-CTGCCTTTATGGATGATGGT-3' (sense), 5'-GTTCAGCTCGAAGAAGA-3' (antisense) for ENaC and 5'-AGGCTACCACAGTCTCCCTG-3' (sense) and 5'-GCAGTGTAAAATCTCCAGTC-3' (antisense) for MCR, showed expression of the ENaC and MCR genes in Müller cells. The presence of ENaC and MCR was detected as the predicted bands of 520 bp and 843 bp, respectively. In both cases, 100% identity was observed between the sequences of rat Müller cell (RMC) PCR products and rat kidney. Interestingly, the basal levels of ENaC were increased in vitro by the MCR-specific hormone, aldosterone. Thus, our results strongly suggest that the Müller glial cells may play a role in the regulation of extracellular Na+ concentration, which could be regulated by steroid-mediated sodium uptake.

Cardiac opioids

Opioid peptides have long been considered as neuropeptides or neurotransmitters. The more recent discovery of these same peptides in non-neuronal tissue suggests that the peptides may have autocrine, paracrine, or endocrine functions as well. The opioid peptides, enkephalins, dynorphins, and endorphins, have been found in isolated cardiac myocytes and heart tissue. This review will cover the recent literature on opioid peptides in respect to cardiac distribution, biochemistry, and function.

Paradoxical effects of mineralocorticoids on the ion gated sodium channel in embryologically diverse cells

PCR analysis and Western blotting revealed the expression of the mineralocorticoid receptor (MCR) and the epithelial sodium channel (ENaC) genes at the level of RNA, DNA, and protein in several leukemic cell lines, fibroblasts from human cornea, and epithelial cells from ocular tissues. Following immunofluorescence, the MCR appeared to be primarily nuclear whereas the ENaC was almost exclusively membrane-bound. Paradoxically, the MCR-specific antagonist ZK 91587 actually stimulated the multiplication of human erythroblastic leukemia cells, contrary to the inhibitory effect of the antagonist RU 26752 on the multiplication of corneal fibroblasts; both effects were opposed by aldosterone. In quantitative PCR, both basal and aldosterone-induced levels of ENaC were diminished by ZK 91587 in the corneal fibroblast, in contrast to the stimulation observed in the retinal pigmentary epithelium. Thus, contrary to the existing notions, (a) antimineralocorticoids can act both as agonists and antagonists, and (b) the receptor-mediated action of mineralocorticoids on the sodium channel is not restricted to the epithelial cell.

General overview of mineralocorticoid hormone action

The adrenal cortex elaborates two major groups of steroids that have been arbitrarily classified as glucocorticoids and mineralocorticoids, despite the fact that carbohydrate metabolism is intimately linked to mineral balance in mammals. In fact, glucocorticoids assured both of these functions in all living cells, animal and photosynthetic, prior to the appearance of aldosterone in teleosts at the dawn of terrestrial colonization. The evolutionary drive for a hormone specifically designed for hydromineral regulation led to zonation for the conversion of 18-hydroxycorticosterone into aldosterone through the catalytic action of a synthase in the secluded compartment of the adrenal zona glomerulosa. Corticoid hormones exert their physiological action by binding to receptors that belong to a transcription factor superfamily, which also includes some of the proteins regulating steroid synthesis. Steroids stimulate sodium absorption by the activation and/or de novo synthesis of the ion-gated, amiloride-sensitive sodium channel in the apical membrane and that of the Na+/K+-ATPase in the basolateral membrane. Receptors, channels, and pumps apparently are linked to the cytoskeleton and are further regulated variously by methylation, phosphorylation, ubiquination, and glycosylation, suggesting a complex system of control at multiple checkpoints. Mutations in genes for many of these different proteins have been described and are known to cause clinical disease.

Epithelial Fluid Transport--A Century of Investigation

Our current understanding of the mechanism of fluid transport by epithelia relies upon mathematical models developed 30 years ago to explain the mechanism of solute-solvent coupling and the pathways taken by water across an epithelium. The validity of these models is reconsidered in light of recent findings, and it is concluded that a simple three-compartment model system is adequate to explain fluid absorption and secretion by epithelia.