Calbindin-D28k, a vitamin D-dependent calcium binding protein, plays a cardinal role in transport of calcium in kidney. Previous studies have demonstrated calbindin-D28k immunoreactivity in the distal nephron of mammalian kidney. However, it is well known that in most species including rat and human, there is a gradual transition from the distal convoluted tubule to the cortical collecting duct, and that the connecting segment do no tclearly demarcated, because of intermingling of distal convoluted tubule cells, connecting tubule cells, principal cells and at least two configurations of intercalated cells. In this study, to identify the cell types of calbindin-D28k-positive cells in distal nephron of rat kidney, we used double immunostaining with an antibody against calbindin-D28k and antibodies against thiazide sensitive Na+/Cl- cotransporter for distal convoluted tubule or H+-ATPase for intercalated cells. In the distal convoluted tubule, most of the distal convoluted tuble cells were calbindin-D28k-positive, whereas the intercalated cells were calbindin-D28k-negative. In the connecting tubule, 68% of the cells were calbindin-D28k-positive, and about 97% of the positive cells were connecting tubule cells and only 3% of them were intercalated cells. In the cortical collecting duct, and outer medullary collecting duct of outer stripe and inner stripe, only 8.6%, 11.8% and 4.4% of cells were weak positive for calbindin-D28k respectively. These weak positive cells in the collecting duct are mainly identified as intercalated cells. These findings indicate that calbindin-D28k is involved in not only transcellular transport of calcium but also processes regulating intracellular calcium in rat kidney.
Animals ; Antibodies ; Calbindin 1 ; Calcium* ; Carrier Proteins* ; Humans ; Immunohistochemistry ; Kidney* ; Nephrons* ; Rats* ; Transcytosis ; Vitamins

Magnesium is the second most common intracellular divalent cation. Magnesium balance in the body is controlled by a dynamic interplay among intestinal absorption, exchange with bone, and renal excretion. Intestinal magnesium absorption proceeds in both a passive paracellular and an active transcellular manner. Regulation of serum magnesium concentrations is achieved mainly by control of renal magnesium reabsorption. Only 20% of filtered magnesium is reabsorbed in the proximal tubule, whereas 60% is reclaimed in the cortical thick ascending limb (TAL) and another 5-10% in the distal convoluted tubule (DCT). The passive paracellular transport of magnesium in the TAL is closely related with the mutations in claudin-16/paracellin-1 and is responsible for familial hypomagnesemia with hypercalciuria and nephrocalcinosis. The active transcellular transport of magnesium in the DCT was similarly enhanced by the realization that defects in transient receptor potential melastatin 6 (TRPM6) cause hypomagnesemia with secondary hypocalcemia. This channel regulates the apical entry of magnesium into epithelia and alters whole-body magnesium homeostasis by controlling urinary excretion. TRPM6 is regulated at the transcriptional level by acid-base status, 17beta-estradiol, and both FK506 and cyclosporine. The molecular identity of the protein responsible for the basolateral exit of magnesium from the epithelial cell remains unidentified.
Absorption ; Cyclosporine ; Epithelial Cells ; Extremities ; Homeostasis ; Hypercalciuria ; Hypocalcemia ; Intestinal Absorption ; Magnesium ; Nephrocalcinosis ; Renal Tubular Transport, Inborn Errors ; Tacrolimus ; Transcytosis ; Transient Receptor Potential Channels

Proton pump inhibitors (PPIs) are widely used though an association with hypomagnesaemia and hypocalcaemia has only been described since 2006. Patients typically present after years of stable dosing with musculoskeletal, neurological or cardiac arrhythmic symptoms, but it is likely that many cases are under-recognised. Magnesium levels resolve rapidly on discontinuation of PPI therapy and hypomagnesaemia recurs rapidly on rechallenge with any agent in the class. The cellular mechanisms of magnesium homeostasis are increasingly being understood, including both passive paracellular absorption through claudins and active transcellular transporters, including the transient receptor potential channels (TRPM6) identified in the intestine and nephron. PPIs may alter luminal pH by modulating pancreatic secretions, affecting non-gastric H+K+ATPase secretion, altering transporter transcription or channel function. A small reduction in intestinal absorption appears pivotal in causing cumulative deficiency. Risk factors have been associated to help identify patients at risk of this effect but clinical vigilance remains necessary for diagnosis.
Absorption ; Claudins ; Diagnosis ; Fatigue ; Homeostasis ; Humans ; Hydrogen-Ion Concentration ; Intestinal Absorption ; Intestines ; Magnesium ; Nephrons ; Phenobarbital ; Proton Pump Inhibitors ; Risk Factors ; Transcytosis ; Transient Receptor Potential Channels

Transient receptor potential vanilloid subtype 1 (TRPV1) was originally found in sensory neurons. Recently, it has been reported that TRPV1 is expressed in salivary gland epithelial cells (SGEC). However, the physiological role of TRPV1 in salivary secretion remains to be elucidated. We found that TRPV1 is expressed in mouse and human submandibular glands (SMG) and HSG cells, originated from human submandibular gland ducts at both mRNA and protein levels. However, capsaicin (CAP), TRPV1 agonist, had little effect on intracellular free calcium concentration ([Ca2+]i) in these cells, although carbachol consistently increased [Ca2+]i. Exposure of cells to high temperature (>43degrees C) or acidic bath solution (pH5.4) did not increase [Ca2+]i, either. We further examined the role of TRPV1 in salivary secretion using TRPV1 knock-out mice. There was no significant difference in the pilocarpine (PILO)-induced salivary flow rate between wild-type and TRPV1 knock-out mice. Saliva flow rate also showed insignificant change in the mice treated with PILO plus CAP compared with that in mice treated with PILO alone. Taken together, our results suggest that although TRPV1 is expressed in SGEC, it appears not to play any direct roles in saliva secretion via transcellular pathway.
Animals ; Baths ; Calcium ; Capsaicin ; Carbachol ; Epithelial Cells* ; Humans ; Mice ; Mice, Knockout ; Pilocarpine ; RNA, Messenger ; Saliva ; Salivary Glands* ; Sensory Receptor Cells ; Submandibular Gland ; Transcytosis*

Bacteremia induced by periodontal infection is an important factor for periodontitis to threaten general health. P. gingivalis DNA/virulence factors have been found in the brain tissues from patients with Alzheimer's disease (AD). The blood-brain barrier (BBB) is essential for keeping toxic substances from entering brain tissues. However, the effect of P. gingivalis bacteremia on BBB permeability and its underlying mechanism remains unclear. In the present study, rats were injected by tail vein with P. gingivalis three times a week for eight weeks to induce bacteremia. An in vitro BBB model infected with P. gingivalis was also established. We found that the infiltration of Evans blue dye and Albumin protein deposition in the rat brain tissues were increased in the rat brain tissues with P. gingivalis bacteremia and P. gingivalis could pass through the in vitro BBB model. Caveolae were detected after P. gingivalis infection in BMECs both in vivo and in vitro. Caveolin-1 (Cav-1) expression was enhanced after P. gingivalis infection. Downregulation of Cav-1 rescued P. gingivalis-enhanced BMECs permeability. We further found P. gingivalis-gingipain could be colocalized with Cav-1 and the strong hydrogen bonding between Cav-1 and arg-specific-gingipain (RgpA) were detected. Moreover, P. gingivalis significantly inhibited the major facilitator superfamily domain containing 2a (Mfsd2a) expression. Mfsd2a overexpression reversed P. gingivalis-increased BMECs permeability and Cav-1 expression. These results revealed that Mfsd2a/Cav-1 mediated transcytosis is a key pathway governing BBB BMECs permeability induced by P. gingivalis, which may contribute to P. gingivalis/virulence factors entrance and the subsequent neurological impairments.
Animals ; Rats ; Bacteremia/metabolism* ; Blood-Brain Barrier/microbiology* ; Caveolin 1/metabolism* ; Gingipain Cysteine Endopeptidases/metabolism* ; Permeability ; Porphyromonas gingivalis/pathogenicity* ; Transcytosis ; Virulence Factors/metabolism*

To produce milk, four secretory processes are synchronized in the alveolar cell of the mature, functional mammary gland: (1) exocytosis, (2) fat synthesis and secretion, (3) secretion of ions and water, and (4) transcytosis of immunoglubulins and other substances from the interstitial space. Milk is synthesized continuously into the alveolar lumen, where it is stored until milk removal from the breast is initiated. Prolactin mediates the central nervous system regulation of milk secretion, but its influence is modified greatly by local factors that depend on milk removal from the breast. Oxytocin mediates milk let-down by stimulating the contraction of myoepithelial cells that surround the alveoli and ducts. Lactogenesis includes all the processes necessary to go from the undifferentiated mammary gland in the early pregnant animal to full lactation sometime after parturition. The most important factors in initiation of lactogenesis stage II appear to be progesterone withdrawal. The metabolic demands of breastfeeding require an increase in maternal metabolism. Postpartum suppression of fertility is thought to be the result of an alteration in pulsatile gonadotropin releasing hormone secretion from the hypothalamus. Women who wish to ensure against pregnancy during lactation usually are advised to use other contraceptive means.
Animals ; Breast ; Breast Feeding ; Central Nervous System ; Contracts ; Dietary Sucrose ; Exocytosis ; Female ; Fertility ; Gonadotropin-Releasing Hormone ; Humans ; Hypothalamus ; Ions ; Lactation ; Mammary Glands, Human ; Milk ; Milk Ejection ; Oxytocin ; Parturition ; Postpartum Period ; Pregnancy ; Progesterone ; Prolactin ; Secretory Pathway ; Transcytosis ; Water