title: Renal interstitial Ca(2+).
abstract: Renal interstitial fluid Ca(2+) concentration ([Ca(2+)](isf)) was measured in anesthetized Wistar rats by using in situ microdialysis. During perfusion of 20 cm of the proximal small intestine with Ca(2+)-free buffer, renal [Ca(2+)](isf) was 1.63 +/- 0.19 mmol/l in the cortex (n = 6) and 1.93 +/- 0.12 mmol/l in the medulla (n = 5, P = 0.223). When Ca(2+) in the intestinal lumen was increased to 3 mmol/l, no change was seen in total or ionized serum Ca(2+) (S(Ca)), urinary Ca(2+) excretion (U(Ca)), or Ca(2+) in a microdialysate of the kidney cortex. Increasing intestinal Ca(2+) further, to 6 mmol/l, was without effect on S(Ca) but significantly increased U(Ca) by 38% and microdialysate Ca(2+) by 36% (1.25 +/- 0.0.09 vs. 1.70 +/- 0. 14 mmol/l, n = 4, P < 0.05). Intravenous infusion of 28 ng. kg(-1). min(-1) of parathyroid hormone for 1 h during perfusion of the intestinal lumen with 1 mmol/ Ca(2+)caused a 7-10% rise in S(Ca), a 40% fall in U(Ca), and a 32% increase in microdialysate Ca(2+) (1.32 +/- 0.13 vs. 1.74 +/- 0.13 mmol/l, n = 6, P < 0.05). Interlobar arteries with a mean diameter of 120 microm were studied by using a wire myograph to determine whether changes in extracellular Ca(2+) affect muscle tone. When precontracted with 5 micromol/l serotonin, the arteries relaxed in response to cumulative addition of Ca(2+) (1-5 mmol/l) with an ED(50) value for Ca(2+) of 3.30 +/- 0.08 mmol/l, n = 3. These data demonstrate that [Ca(2+)](isf) changes dynamically during manipulation of whole-animal Ca(2+) homeostasis and that intrarenal arteries relax in response to extracellular Ca(2+) varied over the range measured in vivo.
authors.affiliation: Section of Hypertension and Vascular Research, University of Texas Medical Branch, Galveston, Texas 77555-1065, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Mupanomunda
authors.forename: B
authors.initials: B
authors.lastname: Tian
authors.forename: N
authors.initials: N
authors.lastname: Ishioka
authors.forename: R D
authors.initials: RD
authors.lastname: Bukoski
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D005110:Extracellular Space / Q000378:metabolism*; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism*; D017551:Microdialysis; D009994:Osmolar Concentration; D010281:Parathyroid Hormone / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012077:Renal Artery / Q000378:metabolism; D014664:Vasodilation / Q000502:physiology
chemical_list: D010281:Parathyroid Hormone; D002118:Calcium