Expression of adrenergic and cholinergic receptors in murine renal intercalated cells

Aquaporins in Urinary System

There are at least eight aquaporins (AQPs) expressed in the kidney. Including AQP1 expressed in proximal tubules, thin descending limb of Henle and vasa recta; AQP2, AQP3, AQP4, AQP5, and AQP6 expressed in collecting ducts; AQP7 expressed in proximal tubules; AQP8 expressed in proximal tubules and collecting ducts; and AQP11 expressed in the endoplasmic reticulum of proximal tubular epithelial cells. Over years, researchers have constructed different AQP knockout mice and explored the effect of AQP knockout on kidney function. Thus, the roles of AQPs in renal physiology are revealed, providing very useful information for addressing fundamental questions about transepithelial water transport and the mechanism of near isoosmolar fluid reabsorption. This chapter introduces the localization and function of AQPs in the kidney and their roles in different kidney diseases to reveal the prospects of AQPs in further basic and clinical studies.

Morphology of Schwann Cell Processes Supports Renal Sympathetic Nerve Terminals With Local Distribution of Adrenoceptors

Nerves in the renal parenchyma comprise sympathetic nerves that act on renal arteries and tubules to decrease blood flow and increase primary urine reabsorption, respectively. Synaptic vesicles release neurotransmitters that activate their effector tissues. However, the mechanisms by which neurotransmitters exert individual responses to renal effector cells remain unknown. Here, we investigated the spatial and molecular compositional associations of renal Schwann cells (SC) supporting the nerve terminals in male rats. The nerve terminals of vascular smooth muscle cells (SMCs) enclosed by renal SC processes were exposed through windows facing the effectors with presynaptic specializations. We found that the adrenergic receptors (ARs) α2A, α2C, and β2 were localized in the SMC and the basal side of the tubules, where the nerve terminals were attached, whereas the other subtypes of ARs were distributed in the glomerular and luminal side, where the norepinephrine released from nerve endings may have indirect access to ARs. In addition, integrins α4 and β1 were coexpressed in the nerve terminals. Thus, renal nerve terminals could contact their effectors via integrins and may have a structure, covered by SC processes, suitable for intensive and directional release of neurotransmitters into the blood, rather than specialized structures in the postsynaptic region.

Urinary reabsorption in the rat kidney by anticholinergics

Anticholinergics, therapeutic agents for overactive bladder, are clinically suggested to reduce urine output. We investigated whether this effect is due to bladder or kidney urine reabsorption. Various solutions were injected into the bladder of urethane-anesthetized SD rats. The absorption rate for 2 h was examined following the intravenous administration of the anticholinergics imidafenacin (IM), atropine (AT), and tolterodine (TO). The bilateral ureter was then canulated and saline was administered to obtain a diuretic state. Anticholinergics or 1-deamino-[8-D-arginine]-vasopressin (dDAVP) were intravenously administered. After the IM and dDAVP administrations, the rat kidneys were immunostained with AQP2 antibody, and intracellular cAMP was measured. The absorption rate was ~ 10% of the saline injected into the bladder and constant even when anticholinergics were administered. The renal urine among peaked 2 h after the saline administration. Each of the anticholinergics significantly suppressed the urine production in a dose-dependent manner, as did dDAVP. IM and dDAVP increased the intracellular cAMP levels and caused the AQP2 molecule to localize to the collecting duct cells' luminal side. The urinary reabsorption mechanism through the bladder epithelium was not activated by anticholinergic administration. Thus, anticholinergics suppress urine production via an increase in urine reabsorption in the kidneys' collecting duct cells via AQP2.

Aquaporins in Urinary System

Several aquaporin (AQP )-type water channels are expressed in kidney: AQP1 in the proximal tubule, thin descending limb of Henle, and vasa recta; AQP2 -6 in the collecting duct; AQP7 in the proximal tubule; AQP8 in the proximal tubule and collecting duct; and AQP11 in the endoplasmic reticulum of proximal tubule cells. AQP2 is the vasopressin-regulated water channel that is important in hereditary and acquired diseases affecting urine-concentrating ability. The roles of AQPs in renal physiology and transepithelial water transport have been determined using AQP knockout mouse models. This chapter describes renal physiologic insights revealed by phenotypic analysis of AQP knockout mice and the prospects for further basic and clinical studies.

Preterm neonatal urinary renal developmental and acute kidney injury metabolomic profiling: an exploratory study

BACKGROUND

Acute kidney injury (AKI) staging has been developed in the adult and pediatric populations, but these do not yet exist for the neonatal population. Metabolomics was utilized to uncover biomarkers of normal and AKI-associated renal function in preterm infants. The study comprised 20 preterm infants with an AKI diagnosis who were matched by gestational age and gender to 20 infants without an AKI diagnosis.

METHODS

Urine samples from pre-term newborn infants collected on day 2 of life were analyzed using broad-spectrum nuclear magnetic resonance (NMR) metabolomics. Multivariate analysis methods were used to identify metabolite profiles that differentiated AKI and no AKI, and to identify a metabolomics profile correlating with gestational age in infants with and without AKI.

RESULTS

There was a clear distinction between the AKI and no-AKI profiles. Two previously identified biomarkers of AKI, hippurate and homovanillate, differentiated AKI from no-AKI profiles. Pathway analysis revealed similarities to cholinergic neurons, prenatal nicotine exposure on pancreatic β cells, and amitraz-induced inhibition of insulin secretion. Additionally, a pH difference was noted. Both pH and the metabolites were found to be associated with AKI; however, only the metabotype was a significant predictor of AKI. Pathways for the no-AKI group that correlated uniquely with gestational age included aminoacyl-t-RNA biosynthesis, whereas pathways in the AKI group yielded potential metabolite changes in pyruvate metabolism.

CONCLUSIONS

Metabolomics was able to differentiate the urinary profiles of neonates with and without an AKI diagnosis and metabolic developmental profiles correlated with gestational age. Further studies in larger cohorts are needed to validate these results.