Taurine and zoo felids: considerations of dietary and biological tissue concentrations

Taurine (TAU) is an essential amino acid required in the diets of Felidae at concentrations ranging between 0.04 and 0.2% on a dry matter (DM) basis (in purified, highly digestible diets, and canned diets, respectively). Although the domestic cat seems to be an appropriate physiologic model for zoo felids, it is sometimes difficult to assess TAU status in zoo feeding programs owing to scattered information on feed ingredient TAU content as well as a lack of normal ranges for assessment of TAU in biological tissues. Knowing that TAU is required in the formulation of hand‐rearing diets for exotic felids, the TAU content of 38 ingredients or products used in zoo carnivore feeding or hand‐rearing programs was summarized, including 21 new feedstuffs for which TAU data were previously lacking. The kitten milk replacer contained a lower than expected value for TAU. Commercially prepared frozen or canned meat products, seafood products, whole rodent prey, and most strained meat jarred baby foods contained adequate TAU; chunk meats, and some specific types of jarred baby food meats were considerably lower in TAU content (≤0.10% DM) than other foodstuffs. TAU concentrations in plasma and whole blood of eight spp. of zoo felids sampled opportunistically fell within reference ranges for domestic cats (80–120 and 300–600 nmol/ml in plasma and whole blood, respectively). Plasma concentrations are a useful measure of dietary impact, whereas whole blood concentrations seem to reflect tissue storage of this nutrient. Zoo Biol 26:517–531, 2007. © 2007 Wiley‐Liss, Inc.     

Effects of media buffer systems on growth and electrophysiologic characteristics of cultured sweat duct cells

Summary Primary cultures of human reabsorptive sweat duct cells were grown in MCDB 170 medium buffered with either HEPES, bicarbonate, or a mixture of HEPES and bicarbonate buffers. Cultures grown in MCDB media containing bicarbonate seemed to differentiate into a multilayered, keratinized epithelium and began senescing after 1 wk in culture. In contrast, cultures grown in media containing HEPES as the only buffer seemed to undergo a selection process, resulting in the outgrowth of cells that did not multilayer or keratinize extensively for up to 3 or 4 wk in culture. Despite marked differences in growth, cells grown in both bicarbonate and HEPES-buffered media retained electrophysiologic characteristics appropriate to the progenitor. Mean resting potentials were −21.8±0.8 mV (n=82), −23.3±1.3 mV (n=70) and −18.2±0.8 mV (n=82) for duct cells grown in HEPES, bicarbonate, and HEPES-bicarbonate media, respectively. Substitution of Cl⁻ with the impermeant anion gluconate in the bathing medium caused membrane potential depolarization in all media, revealing the presence of a Cl⁻ conductance. Administration of the Na⁺ conductance inhibitor amiloride hyperpolarized the mean resting potential of cells grown in HEPES medium (−6.8±0.6 mV,n=68), bicarbonate medium (−6.9±0.5 mV,n=60), and HEPES-bicarbonate medium (−5.9±0.6 mV,n=69), demonstrating expression of a Na⁺ conductance. We observed some but minimal variation with age in any of these conditions. This work was supported by grant DK41329-02 from the National Institute of Health, Bethesda, MD, and a Postdoctoral Fellowship to Dr. Bell from the National Cystic Fibrosis Foundation.     

ENaC Activity Requires CFTR Channel Function Independently of Phosphorylation in Sweat Duct

We previously showed that activation of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) Cl⁻ conductance (gCFTR) supports parallel activation of amiloride-sensitive epithelial Na⁺ channel (ENaC) in the native human sweat duct. However, it is not clear whether phosphorylated CFTR, phosphorylated ENaC, or only Cl⁻ -channel function is required for activation. We used basilaterally α-toxin-permeabilized human sweat ducts to test the hypothesis that ENaC activation depends only on Cl⁻ -channel function and not on phosphorylation of either CFTR or ENaC. CFTR is classically activated by PKA plus millimolar ATP, but cytosolic glutamate activation of gCFTR is independent of ATP and phosphorylation. We show here that both phosphorylation-dependent (PKA) and phosphorylation-independent (glutamate) activation of CFTR Cl⁻ channel function support gENaC activation. We tested whether cytosolic application of 5 mM ATP alone, phosphorylation by cAMP, cGMP, G-protein dependent kinases (all in the presence of 100 μM ATP), or glutamate could support ENaC activation in the absence of gCFTR. We found that none of these agonists activated gENaC by themselves when Cl⁻ current ( ) through CFTR was blocked by: 1) Cl⁻ removal, 2) DIDS inhibition, 3) lowering the ATP concentration to 100 μM (instead of 5 mM required to support CFTR channel function), or 4) mutant CFTR (homozygous ΔF508 CF ducts). However, Cl⁻ gradients in the direction of absorption supported, while Cl⁻ gradients in the direction of secretion prevented ENaC activation. We conclude that the interaction between CFTR and ENaC is dependent on activated through CFTR in the direction of absorption (Cl⁻ gradient from lumen to cell). But such activation of ENaC is independent of phosphorylation and ATP. However, reversing through CFTR in the direction of secretion (Cl⁻ gradient from cell to lumen) prevents ENaC activation even in the presence of through CFTR. An erratum to this article is available at .     

Androgen and estrogen receptors in placental physiology and dysfunction

Background

The placenta is recognized as an endocrine organ, largely due to its secretions of steroid hormones, including progesterone, androgens, and estrogens. Steroid hormones play an essential role in the progression of pregnancy, fetal development, and growth. Furthermore, steroids are necessary for establishment and maintenance of a normal pregnancy, preparing the endometrium for implantation, stimulating endometrial secretions, and regulating uterine blood flow, however the exact mechanism of sex steroid signaling through their receptors in placental function is unknown.

Objective

In this review, we will provide an overview of the current knowledge on sex steroid receptors in normal placental development, as well as evidence of abnormal signaling associated with placental dysfunction.

Methods

A systematic literature search was performed using the NCBI PubMed search engine, including the following key works: estrogen receptor, androgen receptor, placenta, placental development, cytotrophoblast, and differentiation.

Results

Of the over 700 articles that were returned, 125 studies focused on estrogen and androgen receptors in human placenta development and function during normal and abnormal pregnancy, as well as in rodents and ruminants placentae.

Conclusion

Receptors for both estrogens and androgens have been localized within the mammalian placenta, but surprisingly little is known about their signaling in trophoblast cell differentiation and function. An emerging picture is developing in which estrogen receptors possibly play role in cytotrophoblast proliferation and extravillous trophoblast invasion, whereas androgen receptors are involved in syncytiotrophoblast differentiation and function.

     

Molecular phylogeny of the springhare, Pedetes capensis, based on mitochondrial DNA sequences

The phylogenetic position of the Pedetidae, represented by a single species Pedetes capensis, is controversial, reflecting in part the retention of both Hystricomorphous and Sciurognathous characteristics in this rodent. In an attempt to clarify the species evolutionary relationships, mtDNA gene sequences from 10 rodent species (representing seven families) were analyzed using phenetic, parsimony, and maximum-likelihood methods of phylogenetic inference; the rabbit, Oryctolagus cuniculus (Order Lagomorpha), and cow, Bos taurus (Order Artiodactyla), were used as outgroups. Investigation of 714 base pairs of the protein-coding cytochrome b gene indicate strong base bias at the third codon position with significant rate heterogeneity evident between the three structural domains of this gene. Similar analyses conducted on 816 base pairs of the 12S rRNA gene revealed a transversion bias in the loop sections of all taxa. The cytochrome b gene sequences proved useful in resolving associations between closely related species but failed to produce consistent tree topologies at the family level. In contrast, phylogenetic analysis of the 12S rRNA gene resulted in strong support for the clustering of Pedetidae/Heteromyidae/Geomyidae and Muridae in one clade to the exclusion of the Hystricidae/Thryonomyidae and Sciuridae, a finding which is concordant with studies of rodent fetal membranes as well as reproductive and other anatomical features.