scholarly journals Architecture of vasa recta in the renal inner medulla of the desert rodent Dipodomys merriami: potential impact on the urine concentrating mechanism

2012 ◽  
Vol 303 (7) ◽  
pp. R748-R756 ◽  
Author(s):  
Tadeh Issaian ◽  
Vinoo B. Urity ◽  
William H. Dantzler ◽  
Thomas L. Pannabecker
Keyword(s):  
Water Channel ◽  
Wistar Rat ◽  
Vascular Bundles ◽  
Dipodomys Merriami ◽  
Kangaroo Rat ◽  
Concentrating Mechanism ◽  
Architectural Features ◽  
Vasa Recta ◽  
Desert Rodent ◽  
Urine Concentrating Mechanism

We hypothesize that the inner medulla of the kangaroo rat Dipodomys merriami, a desert rodent that concentrates its urine to over 6,000 mosmol/kg H2O, provides unique examples of architectural features necessary for production of highly concentrated urine. To investigate this architecture, inner medullary vascular segments in the outer inner medulla were assessed with immunofluorescence and digital reconstructions from tissue sections. Descending vasa recta (DVR) expressing the urea transporter UT-B and the water channel aquaporin 1 lie at the periphery of groups of collecting ducts (CDs) that coalesce in their descent through the inner medulla. Ascending vasa recta (AVR) lie inside and outside groups of CDs. DVR peel away from vascular bundles at a uniform rate as they descend the inner medulla, and feed into networks of AVR that are associated with organized clusters of CDs. These AVR form interstitial nodal spaces, with each space composed of a single CD, two AVR, and one or more ascending thin limbs or prebend segments, an architecture that may lead to solute compartmentation and fluid fluxes essential to the urine concentrating mechanism. Although we have identified several apparent differences, the tubulovascular architecture of the kangaroo rat inner medulla is remarkably similar to that of the Munich Wistar rat at the level of our analyses. More detailed studies are required for identifying interspecies functional differences.

scholarly journals Architecture of kangaroo rat inner medulla: segmentation of descending thin limb of Henle's loop

2012 ◽  
Vol 302 (6) ◽  
pp. R720-R726 ◽  
Author(s):  
Vinoo B. Urity ◽  
Tadeh Issaian ◽  
Eldon J. Braun ◽  
William H. Dantzler ◽  
Thomas L. Pannabecker
Keyword(s):  
Water Flux ◽  
Urine Osmolality ◽  
Wistar Rat ◽  
Structural Features ◽  
Dipodomys Merriami ◽  
Tissue Sections ◽  
Kangaroo Rat ◽  
Architectural Features ◽  
Collecting Ducts ◽  
Specific Proteins

We hypothesize that the inner medulla of the kangaroo rat Dipodomys merriami , a desert rodent that concentrates its urine to more than 6,000 mosmol/kgH2O water, provides unique examples of architectural features necessary for production of highly concentrated urine. To investigate this architecture, inner medullary nephron segments in the initial 3,000 μm below the outer medulla were assessed with digital reconstructions from physical tissue sections. Descending thin limbs of Henle (DTLs), ascending thin limbs of Henle (ATLs), and collecting ducts (CDs) were identified by immunofluorescence using antibodies that label segment-specific proteins associated with transepithelial water flux (aquaporin 1 and 2, AQP1 and AQP2) and chloride flux (the chloride channel ClC-K1); all tubules and vessels were labeled with wheat germ agglutinin. In the outer 3,000 μm of the inner medulla, AQP1-positive DTLs lie at the periphery of groups of CDs. ATLs lie inside and outside the groups of CDs. Immunohistochemistry and reconstructions of loops that form their bends in the outer 3,000 μm of the inner medulla show that, relative to loop length, the AQP1-positive segment of the kangaroo rat is significantly longer than that of the Munich-Wistar rat. The length of ClC-K1 expression in the prebend region at the terminal end of the descending side of the loop in kangaroo rat is about 50% shorter than that of the Munich-Wistar rat. Tubular fluid of the kangaroo rat DTL may approach osmotic equilibrium with interstitial fluid by water reabsorption along a relatively longer tubule length, compared with Munich-Wistar rat. A relatively shorter-length prebend segment may promote a steeper reabsorptive driving force at the loop bend. These structural features predict functionality that is potentially significant in the production of a high urine osmolality in the kangaroo rat.

A region-based mathematical model of the urine concentrating mechanism in the rat outer medulla. II. Parameter sensitivity and tubular inhomogeneity

2005 ◽  
Vol 289 (6) ◽  
pp. F1367-F1381 ◽  
Author(s):  
Anita T. Layton ◽  
Harold E. Layton
Keyword(s):  
Mathematical Model ◽  
Boundary Conditions ◽  
Rat Kidney ◽  
Vascular Bundles ◽  
Thick Ascending Limb ◽  
Outer Medulla ◽  
Model Calculations ◽  
Concentrating Mechanism ◽  
Vasa Recta ◽  
Urine Concentrating Mechanism

In a companion study (Layton AT and Layton HE. Am J Physiol Renal Physiol 289: F1346–F1366, 2005), a region-based mathematical model was formulated for the urine concentrating mechanism (UCM) in the outer medulla (OM) of the rat kidney. In the present study, we quantified the sensitivity of that model to several structural assumptions, including the degree of regionalization and the degree of inclusion of short descending limbs (SDLs) in the vascular bundles of the inner stripe (IS). Also, we quantified model sensitivity to several parameters that have not been well characterized in the experimental literature, including boundary conditions, short vasa recta distribution, and ascending vasa recta (AVR) solute permeabilities. These studies indicate that regionalization elevates the osmolality of the fluid delivered into the inner medulla via the collecting ducts; that model predictions are not significantly sensitive to boundary conditions; and that short vasa recta distribution and AVR permeabilities significantly impact concentrating capability. Moreover, we investigated, in the context of the UCM, the functional significance of several aspects of tubular segmentation and heterogeneity: SDL segments in the IS that are likely to be impermeable to water but highly permeable to urea; a prebend segment of SDLs that may be functionally like thick ascending limb (TAL); differing IS and outer stripe Na+ active transport rates in TAL; and potential active urea secretion into the proximal straight tubules. Model calculations predict that these aspects of tubular of segmentation and heterogeneity generally enhance solute cycling or promote effective UCM function.

scholarly journals Comparative physiology and architecture associated with the mammalian urine concentrating mechanism: role of inner medullary water and urea transport pathways in the rodent medulla

2013 ◽  
Vol 304 (7) ◽  
pp. R488-R503 ◽  
Author(s):  
Thomas L. Pannabecker
Keyword(s):  
Water Channel ◽  
Urine Concentration ◽  
Structure And Function ◽  
Transport Pathways ◽  
Regulatory Pathways ◽  
Concentrating Mechanism ◽  
Vasa Recta ◽  
And Function ◽  
Tissue Compartments ◽  
Urine Concentrating Mechanism

Comparative studies of renal structure and function have potential to provide insights into the urine-concentrating mechanism of the mammalian kidney. This review focuses on the tubular transport pathways for water and urea that play key roles in fluid and solute movements between various compartments of the rodent renal inner medulla. Information on aquaporin water channel and urea transporter expression has increased our understanding of functional segmentation of medullary thin limbs of Henle's loops, collecting ducts, and vasa recta. A more complete understanding of membrane transporters and medullary architecture has identified new and potentially significant interactions between these structures and the interstitium. These interactions are now being introduced into our concept of how the inner medullary urine-concentrating mechanism works. A variety of regulatory pathways lead directly or indirectly to variable patterns of fluid and solute movements among the interstitial and tissue compartments. Animals with the ability to produce highly concentrated urine, such as desert species, are considered to exemplify tubular structure and function that optimize urine concentration. These species may provide unique insights into the urine-concentrating process. 1

Outer medullary anatomy and the urine concentrating mechanism

1998 ◽  
Vol 274 (2) ◽  
pp. F413-F424 ◽  
Author(s):  
X. Wang ◽  
S. R. Thomas ◽  
A. S. Wexler
Keyword(s):  
Structural Model ◽  
Comparative Anatomy ◽  
Urine Concentration ◽  
Vascular Bundles ◽  
Vasa Recta ◽  
Collecting Ducts ◽  
Outer Stripe ◽  
Physiological Values ◽  
Modeling Representation ◽  
Urine Concentrating Mechanism

In earlier work, mathematical models of the urine concentration mechanism were developed incorporating the features of renal anatomy. However, several anatomic observations showed inconsistencies in the modeling representation of the outer stripe (OS) anatomy. In this study, based on observations from comparative anatomy and morphometric studies, we propose a new structural model of outer medullary anatomy, different from that previously presented [A. S. Wexler, R. E. Kalaba, and D. J. Marsh. Am. J. Physiol. 260 ( Renal Fluid Electrolyte Physiol. 29): F368–F383, 1991]. The modifications include the following features of rat outer medullary anatomy, for example, 1) in the OS, the limbs of long loops of Henle surround the descending and ascending vasa recta that develop into the vascular bundles in the inner stripe (IS), whereas the limbs of short loops are close to the collecting ducts; and 2) the descending limbs of short loops shift from the tubular region in the OS to near the vascular bundle in the IS, whereas the limbs of long loops are situated away from the vascular bundles in the tubular region. The sensitivity of the concentrating process to the relative position of loops and vessels was investigated in the different medullary regions. With these modifications, the model predicts a more physiological, axial osmolarity gradient in both outer and inner medulla with membrane parameters that are all in the range of measured physiological values, including the urea permeabilities of descending vasa recta reported by Pallone and co-workers (T. L. Pallone, J. Work, R. L. Myers, and R. L. Jamison. J. Clin.Invest. 93: 212–222, 1994).

Inner medullary lactate production and urine-concentrating mechanism: a flat medullary model

2003 ◽  
Vol 284 (1) ◽  
pp. F65-F81 ◽  
Author(s):  
Stéphane Hervy ◽  
S. Randall Thomas
Keyword(s):  
Collecting Duct ◽  
Lactate Production ◽  
Osmotic Gradient ◽  
Osmotic Effect ◽  
Concentrating Mechanism ◽  
Urea Permeability ◽  
Vasa Recta ◽  
Renal Inner Medulla ◽  
High Lactate ◽  
Urine Concentrating Mechanism

We used a mathematical model to explore the possibility that metabolic production of net osmoles in the renal inner medulla (IM) may participate in the urine-concentrating mechanism. Anaerobic glycolysis (AG) is an important source of energy for cells of the IM, because this region of the kidney is hypoxic. AG is also a source of net osmoles, because it splits each glucose into two lactate molecules, which are not metabolized within the IM. Furthermore, these sugars exert their full osmotic effect across the epithelia of the thin descending limb of Henle's loop and the collecting duct, so they are apt to fulfill the external osmole role previously attributed to interstitial urea (whose role is compromised by the high urea permeability of long descending limbs). The present simulations show that physiological levels of IM glycolytic lactate production could suffice to significantly amplify the IM accumulation of NaCl. The model predicts that for this to be effective, IM lactate recycling must be efficient, which requires high lactate permeability of descending vasa recta and reduced IM blood flow during antidiuresis, two conditions that are probably fulfilled under normal circumstances. The simulations also suggest that the resulting IM osmotic gradient is virtually insensitive to the urea permeability of long descending limbs, thus lifting a longstanding paradox, and that this high urea permeability may serve for independent regulation of urea balance.

scholarly journals Architecture of interstitial nodal spaces in the rodent renal inner medulla

2013 ◽  
Vol 305 (5) ◽  
pp. F745-F752 ◽  
Author(s):  
Rebecca L. Gilbert ◽  
Thomas L. Pannabecker
Keyword(s):  
Collecting Duct ◽  
Critical Role ◽  
Wistar Rat ◽  
Osmotic Gradient ◽  
Number Density ◽  
Strong Argument ◽  
Kangaroo Rat ◽  
Vasa Recta ◽  
Renal Inner Medulla ◽  
Abundant Supply

Every collecting duct (CD) of the rat inner medulla is uniformly surrounded by about four abutting ascending vasa recta (AVR) running parallel to it. One or two ascending thin limbs (ATLs) lie between and parallel to each abutting AVR pair, opposite the CD. These structures form boundaries of axially running interstitial compartments. Viewed in transverse sections, these compartments appear as four interstitial nodal spaces (INSs) positioned symmetrically around each CD. The axially running compartments are segmented by interstitial cells spaced at regular intervals. The pairing of ATLs and CDs bounded by an abundant supply of AVR carrying reabsorbed water, NaCl, and urea make a strong argument that the mixing of NaCl and urea within the INSs and countercurrent flows play a critical role in generating the inner medullary osmotic gradient. The results of this study fully support that hypothesis. We quantified interactions of all structures comprising INSs along the corticopapillary axis for two rodent species, the Munich-Wistar rat and the kangaroo rat. The results showed remarkable similarities in the configurations of INSs, suggesting that the structural arrangement of INSs is a highly conserved architecture that plays a fundamental role in renal function. The number density of INSs along the corticopapillary axis directly correlated with a loop population that declines exponentially with distance below the outer medullary-inner medullary boundary. The axial configurations were consistent with discrete association between near-bend loop segments and INSs and with upper loop segments lying distant from INSs.

scholarly journals Role of three-dimensional architecture in the urine concentrating mechanism of the rat renal inner medulla

2008 ◽  
Vol 295 (5) ◽  
pp. F1271-F1285 ◽  
Author(s):  
Thomas L. Pannabecker ◽  
William H. Dantzler ◽  
Harold E. Layton ◽  
Anita T. Layton
Keyword(s):  
Three Dimensional ◽  
Cluster System ◽  
Urea Transporter ◽  
Comprehensive Understanding ◽  
Concentrating Mechanism ◽  
Vasa Recta ◽  
Collecting Ducts ◽  
Renal Inner Medulla ◽  
Urine Concentrating Mechanism

Recent studies of three-dimensional architecture of rat renal inner medulla (IM) and expression of membrane proteins associated with fluid and solute transport in nephrons and vasculature have revealed structural and transport properties that likely impact the IM urine concentrating mechanism. These studies have shown that 1) IM descending thin limbs (DTLs) have at least two or three functionally distinct subsegments; 2) most ascending thin limbs (ATLs) and about half the ascending vasa recta (AVR) are arranged among clusters of collecting ducts (CDs), which form the organizing motif through the first 3–3.5 mm of the IM, whereas other ATLs and AVR, along with aquaporin-1-positive DTLs and urea transporter B-positive descending vasa recta (DVR), are external to the CD clusters; 3) ATLs, AVR, CDs, and interstitial cells delimit interstitial microdomains within the CD clusters; and 4) many of the longest loops of Henle form bends that include subsegments that run transversely along CDs that lie in the terminal 500 μm of the papilla tip. Based on a more comprehensive understanding of three-dimensional IM architecture, we distinguish two distinct countercurrent systems in the first 3–3.5 mm of the IM (an intra-CD cluster system and an inter-CD cluster system) and a third countercurrent system in the final 1.5–2 mm. Spatial arrangements of loop of Henle subsegments and multiple countercurrent systems throughout four distinct axial IM zones, as well as our initial mathematical model, are consistent with a solute-separation, solute-mixing mechanism for concentrating urine in the IM.

Cochlear Potentials in the Kangaroo Rat, Dipodomys merriami

1971 ◽  
Vol 44 (2) ◽  
pp. 112-118 ◽  
Author(s):  
Jack Vernon ◽  
Paul Herman ◽  
Ernest Peterson
Keyword(s):  
Dipodomys Merriami ◽  
Kangaroo Rat ◽  
Cochlear Potentials
Sign in / Sign up

Export Citation Format

Share Document