Lithium distribution across the membrane of motoneurons in the isolated frog spinal cord

Lithium sensitive microelectrodes were used to investigate the transmembrane distribution of lithium ions (Li+) in motoneurons of the isolated frog spinal cord. After addition of 5 mmol·l–1 LiCl to the bathing solution the extracellular diffusion of Li+ was measured. At a depth of 500 m, about 60 min elapsed before the extracellular Li+ concentration approached that of the bathing solution. Intracellular measurements revealed that Li+ started to enter the cells soon after reaching the motoneuron pool and after up to 120 min superfusion, an intra — to extracellular concentration ratio of about 0.7 was obtained. The resting membrane potential and height of antidromically evoked action potentials were not altered by 5 mmol·l–1 Li+

Explaining variability in ciclosporin exposure in adult kidney transplant recipients

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Functional Analysis of Alleged NOGGIN Mutation G92E Disproves Its Pathogenic Relevance

We identified an amino acid change (p.G92E) in the Bone Morphogenetic Protein antagonist NOGGIN in a 22-month-old boy who presented with a unilateral brachydactyly type B phenotype. Brachydactyly type B is a skeletal malformation that has been associated with increased Bone Morphogenetic Protein pathway activation in other patients. Previously, the amino acid change p.G92E in NOGGIN was described as causing fibrodysplasia ossificans progressiva, a rare genetic disorder characterized by limb malformations and progressive heterotopic bone formation in soft tissues that, like Brachydactyly type B, is caused by increased activation of Bone Morphogenetic Protein signaling. To determine whether G92E-NOGGIN shows impaired antagonism that could lead to increased Bone Morphogenetic Protein signaling, we performed functional assays to evaluate inhibition of BMP signaling. Interestingly, wt-NOGGIN shows different inhibition efficacies towards various Bone Morphogenetic Proteins that are known to be essential in limb development. However, comparing the biological activity of G92E-NOGGIN with wt-NOGGIN, we observed that G92E-NOGGIN inhibits activation of bone morphogenetic protein signaling with equal efficiency as wt-NOGGIN, supporting that G92E-NOGGIN does not cause pathological effects. Genetic testing of the child's parents revealed the same amino acid change in the healthy father, further supporting that p.G92E is a neutral amino acid substitution in NOGGIN. We conclude that p.G92E represents a rare polymorphism of the NOGGIN gene - causing neither brachydactyly nor fibrodysplasia ossificans progressiva. This study highlights that a given genetic variation should not be considered pathogenic unless supported by functional analyses

Expression of Tas1 Taste Receptors in Mammalian Spermatozoa: Functional Role of Tas1r1 in Regulating Basal Ca2+ and cAMP Concentrations in Spermatozoa

Background: During their transit through the female genital tract, sperm have to recognize and discriminate numerous chemical compounds. However, our current knowledge of the molecular identity of appropriate chemosensory receptor proteins in sperm is still rudimentary. Considering that members of the Tas1r family of taste receptors are able to discriminate between a broad diversity of hydrophilic chemosensory substances, the expression of taste receptors in mammalian spermatozoa was examined. Methodology/Principal Findings: The present manuscript documents that Tas1r1 and Tas1r3, which form the functional receptor for monosodium glutamate (umami) in taste buds on the tongue, are expressed in murine and human spermatozoa, where their localization is restricted to distinct segments of the flagellum and the acrosomal cap of the sperm head. Employing a Tas1r1-deficient mCherry reporter mouse strain, we found that Tas1r1 gene deletion resulted in spermatogenic abnormalities. In addition, a significant increase in spontaneous acrosomal reaction was observed in Tas1r1 null mutant sperm whereas acrosomal secretion triggered by isolated zona pellucida or the Ca2+ ionophore A23187 was not different from wild-type spermatozoa. Remarkably, cytosolic Ca2+ levels in freshly isolated Tas1r1-deficient sperm were significantly higher compared to wild-type cells. Moreover, a significantly higher basal cAMP concentration was detected in freshly isolated Tas1r1-deficient epididymal spermatozoa, whereas upon inhibition of phosphodiesterase or sperm capacitation, the amount of cAMP was not different between both genotypes. Conclusions/Significance: Since Ca2+ and cAMP control fundamental processes during the sequential process of fertilization, we propose that the identified taste receptors and coupled signaling cascades keep sperm in a chronically quiescent state until they arrive in the vicinity of the egg - either by constitutive receptor activity and/or by tonic receptor activation by gradients of diverse chemical compounds in different compartments of the female reproductive tract