Functional characteristics of NaS2, a placenta-specific Na+-coupled transporter for sulfate and oxyanions of the micronutrients selenium and chromium.

NaS2 is a Na+-coupled transporter for sulfate that belongs to the SLC13 gene family. This transporter was originally cloned from high endothelial venule endothelial cells, but nothing is known about the functional characteristics of this transporter except that it transports sulfate in a Na+-coupled manner. Northern blot analysis indicates that NaS2 is expressed most robustly in placenta. In the present study, we cloned NaS2 from rat placenta and characterized its transport function in detail using the Xenopus laevis oocyte expression system. Rat NaS2 consists of 629 amino acids and is highly similar to human NaS2. In situ hybridization studies with mouse placental sections show that NaS2 transcripts are expressed primarily in trophoblasts of the labyrinth zone. The expression of the transporter is confirmed in primary cultures of trophoblasts isolated from human placenta. When expressed in X. laevis oocytes, rat NaS2 mediates Na+-coupled transport of sulfate. The transport of sulfate is inhibited by oxyanions of selenium, chromium, arsenic, molybdenum, and phosphorous, suggesting that the transporter may mediate the transport of these oxyanions in addition to sulfate. The Kt for sulfate is 153+/-30 microM and the Na+:sulfate stoichiometry is 3:1. The transport process is electrogenic as evidenced from the inhibition of the uptake process by K+-induced depolarization. We conclude that NaS2 is a placenta-specific Na+-coupled, electrogenic, transporter for sulfate expressed in trophoblasts and that it is also responsible for the transport of oxyanions of the micronutrients selenium and chromium.

Development and distribution of pathologic lesions are related to immune status and tissue deposition of human granulocytic ehrlichiosis agent-infected cells in a murine model system.

To evaluate pathology and the role of immune status in a murine model system of human granulocytic ehrlichiosis (HGE), C3H/HeJ, C3H-SCID, and Peromyscus leucopus mice were infected with an HGE agent. All mice remained healthy. Ehrlichemia was not detected after day 14 in P. leucopus and C3H/HeJ mice but increased between days 14 and 90 in C3H-SCID mice. In tissues examined at day 21 and later, infection was rarely detected in immunocompetent mice but was present in all C3H-SCID mice and included pulmonary endothelialitis and hepatic mononuclear cell aggregates with apoptoses. HGE agent was demonstrated in mature and immature myeloid cells in hematopoietic tissues and infrequently in lung and liver lesions with deposition of infected cells. HGE agent infection in immunocompromised mice progresses slowly, has a higher infectious burden and more tissue pathology and is persistent. A murine model for HGE may be useful to assess pathologic lesions, transmission, and persistence.

Sperm storage in the oviduct of the tropical rock lizard, Psammophilus dorsalis.

The female rock lizard, Psammophilus dorsalis (Agamidae), lays multiple clutches of eggs over a period of 6 months (June-December). The later clutches of eggs are presumably fertilized by sperm stored from earlier matings, since testes and epididymides are regressed after August. Sperm storage is seen in pockets of the anterior vaginal region of the oviduct. Sperm recovered from the uterovaginal region are intact and motile. Discrete granules resembling the secretory granules present in the vas deferens also occur along with sperm in the vaginal sperm storage structures. The PAS-positive granules and acid phosphatase form important components of the secretions present along with sperm in the vaginal sperm storage pockets. The epithelium of the vaginal sperm storage pockets is PAS-positive and contains lipid. Several enzymes, including hydroxysteroid dehydrogenases and hydrolases, are localized histochemically in the epithelium of the vaginal sperm storage pockets. A possible role is suggested for the secretions from the male reproductive tract during sperm storage in the oviduct, in which physiological "dormancy" of the sperm during their storage may be maintained by the metabolic "milieu" in the vaginal sperm storage pockets by a mechanism similar to that effecting dormancy of the epididymal sperm in the male. © 1995 Wiley-Liss, Inc.

Electrogenic nature of rat sodium-dependent multivitamin transport.

We report on the electrogenic nature of the transport process mediated by the rat sodium-dependent multivitamin transporter. In Cos-7 cells, the relationship of Na(+) concentration versus biotin and pantothenate uptake rate was sigmoidal with a Na(+):substrate stoichiometry of 2:1. In Cos-7 cells expressing rat SMVT biotin transport was significantly higher when the membrane was hyperpolarized and considerably reduced when the membrane was depolarized. Similarly, biotin uptake in X. laevis oocytes expressing rat SMVT was inhibited with depolarized oocyte membrane by altering the K(+) permeability across the membrane. It is concluded that the transport of biotin and pantothenate mediated by rat SMVT is electrogenic with a Na(+):substrate coupling ratio of 2:1 and that the transport process is associated with the transfer of one net positive charge across the membrane per transport cycle.