The urothelium of a hibernator: the American black bear. Issue 6 (24th June 2015)

• Record Type: Journal Article
• Authors: Spector, David A.; Deng, Jie; Coleman, Richard; Wade, James B.
• Is Part Of: Physiological reports. Volume 3:Issue 6(2015:Jun.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2015-06-24
• Subjects: Black bear -- hibernation -- urinary bladder microscopy -- urine reabsorption -- urothelium; Physiology -- Periodicals; 571
• DOI: 10.14814/phy2.12429
• Languages: English
• ISSNs: 2051-817X

Abstract

Abstract: The American black bear undergoes a 3–5 month winter hibernation during which time bears do not eat, drink, defecate, or urinate. During hibernation renal function (GFR) is 16–50% of normal but urine is reabsorbed across the urinary bladder (UB) urothelium thus enabling metabolic recycling of all urinary constituents. To elucidate the mechanism(s) whereby urine is reabsorbed, we examined the UBs of five nonhibernating wild bears using light, electron (EM), and confocal immunofluorescent (IF) microscopy–concentrating on two components of the urothelial permeability barrier – the umbrella cell apical membranes and tight junctions (TJ). Bear UB has the same tissue layers (serosa, muscularis, lamina propria, urothelia) and its urothelia has the same cell layers (basal, intermediate, umbrella cells) as other mammalians. By EM, the bear apical membrane demonstrated a typical mammalian scalloped appearance with hinge and plaque regions – the latter containing an asymmetric trilaminar membrane and, on IF, uroplakins Ia, IIIa, and IIIb. The umbrella cell TJs appeared similar to those in other mammals and also contained TJ proteins occludin and claudin ‐ 4, and not claudin –2. Thus, we were unable to demonstrate urothelial apical membrane or TJ differences between active black bears and other mammals. Expression and localization of UT‐B, AQP‐1 and ‐3, and Na +, K + ‐ATPase on bear urothelial membranes was similar to that of other mammals. Similar studies of urothelia of hibernating bears, including evaluation of the apical membrane lipid bilayer and GAGs layer are warranted to elucidate the mechanism(s) whereby hibernating bears reabsorb their daily urine output and thus ensure successful hibernation. Abstract : The American Black Bear reabsorbs all urine across the urinary bladder and does not urinate during its 3–5 month hibernation. The urothelium of black bear urinary bladder was investigated in five nonhibernating wild bears using light, electron, and immunofluorescent microscopy and found to be similar to the urothelium of nonhibernating mammals. The mechanism whereby bears reabsorb (and thus recycle) all urinary constituents across urinary bladder during hibernation remains a mystery.