Functional, molecular, and biochemical characterization of streptozotocin-induced diabetes.
Altered divalent cation homeostasis with bone mineral loss, hypercalciuria, and hypomagnesemia have been associated consistently with human diabetes mellitus. This study investigated functional, molecular, and biochemical determinants that accompany this condition in chronically (2 wk) streptozotocin (STZ)-diabetic rats. Catheterized, conscious, diabetic rats on servo-controlled fluid replacement exhibited an increased GFR (+70%) and a substantially raised urinary calcium output (+568%) when compared with control rats. In addition, fractional calcium reabsorption was reduced, indicating that the hypercalciuria was not due solely to an osmotic effect but may involve an actual tubular defect. The expression of proteins involved in renal distal Ca2+ and water transport in STZ-diabetic rats were then studied by Western analysis and immunofluorescence microscopy to investigate the molecular basis of the hypercalciuria. Extracellular Ca2+-sensing receptor abundance was reduced to 52% of control in STZ-diabetes, whereas thiazide-sensitive NaCl cotransporter expression was increased by 192%. Subcutaneous insulin implant rectified both functional and molecular parameters. The levels of calbindin D(28k), plasma membrane Ca2+ ATPase, and aquaporin 1 in whole kidney and of aquaporin 2 in inner medulla were unchanged in diabetic and/or insulin replacement. Blood levels of 1,25(OH)(2)D(3) were reduced in diabetes as were levels of osteocalcin, a marker of bone formation. It is concluded that diabetic hypercalciuria in rats involves elevated GFR with raised urinary output, reduced Ca2+ reabsorption, and impaired bone deposition. Changes in Ca2+-sensing receptor and NaCl cotransporter protein expression could account for the altered divalent cation homeostasis seen during diabetes mellitus.
School of Biological Sciences, University of Manchester, Manchester, United Kingdom.
Donald T
DT
Ward
School of Biological Sciences, University of Manchester, Manchester, United Kingdom.
S Kam
SK
Yau
University School of Medicine, Manchester Royal Infirmary, Manchester, United Kingdom.
Andrew P
AP
Mee
University School of Medicine, Manchester Royal Infirmary, Manchester, United Kingdom.
E Barbara
EB
Mawer
School of Biological Sciences, University of Manchester, Manchester, United Kingdom.
Christopher A
CA
Miller
School of Biological Sciences, University of Manchester, Manchester, United Kingdom.
Hugh O
HO
Garland
School of Biological Sciences, University of Manchester, Manchester, United Kingdom.
Daniela
D
Riccardi
D000818:Animals; D020346:Aquaporins / Q000378:metabolism; D064026:Calbindins; D002117:Calcitriol / Q000097:blood; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D003921:Diabetes Mellitus, Experimental / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology*; D005110:Extracellular Space / Q000378:metabolism; D007668:Kidney / Q000503:physiopathology; D008297:Male; D015675:Osteocalcin / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000378:metabolism; D011955:Receptors, Drug; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D049992:Sodium Chloride Symporters; D028021:Sodium-Potassium-Chloride Symporters; D064486:Solute Carrier Family 12, Member 3; D027981:Symporters
D020346:Aquaporins; D064026:Calbindins; D002352:Carrier Proteins; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; D011955:Receptors, Drug; D064030:S100 Calcium Binding Protein G; C578876:Slc12a3 protein, rat; D049992:Sodium Chloride Symporters; D028021:Sodium-Potassium-Chloride Symporters; D064486:Solute Carrier Family 12, Member 3; D027981:Symporters; C473605:extracellular calcium cation-sensing receptor, rat; C064415:thiazide receptor; D015675:Osteocalcin; D000252:Calcium-Transporting ATPases; D002117:Calcitriol