title: Extracellular polyamines regulate fluid secretion in rat colonic crypts via the extracellular calcium-sensing receptor.
abstract: OBJECTIVE
  Polyamines are essential for the normal postnatal development, maintenance, and function of gastrointestinal epithelia. The extracellular Ca(2+) (Ca(2+)(o)/nutrient)-sensing receptor is expressed on both luminal and basolateral membranes of colonocytes, and, in other cell systems, this receptor has been shown to respond to polyamines. Thus, the Ca(2+)-sensing receptor could provide a mechanism for modulation of colonocyte function by dietary and systemic extracellular polyamines. In the present study, we investigated the interaction of polyamines, particularly spermine, and extracellular Ca(2+) on second messenger generation by, and on function of, rat distal colonic crypts.
  
  
  METHODS
  Calcium-sensing receptor activation was assessed in colonic epithelial cells and intact crypts freshly isolated from distal colon by monitoring intracellular IP(3) and Ca(2+) accumulation using radioimmunoassay and Fluo-3 fluorometry, respectively. Interactions of extracellular Ca(2+) and spermine on regulation of both basal and forskolin-stimulated fluid transport were measured in crypts microperfused in vitro.
  
  
  RESULTS
  Polyamine (spermine > spermidine > putrescine)-mediated enhancement of intracellular D-myo-inositol 1,4,5-trisphosphate (IP(3)) and Ca(2+) accumulation required extracellular Ca(2+), and the EC(50) for extracellular Ca(2+)-mediated activation of the calcium-sensing receptor was reduced by polyamines. Extracellular spermine modulated both basal and forskolin-stimulated fluid secretion in perfused colonic crypts, and the EC(50) for spermine-induced reduction in forskolin-stimulated fluid secretion was inversely dependent on extracellular Ca(2+) (Ca(2+)(o)).
  
  
  CONCLUSIONS
  The interactions of extracellular Ca(2+) and polyamines on second messenger accumulation and fluid secretion support a role for the luminal and basolateral calcium-sensing receptors in mediating some of the effects of polyamines on distal colonic epithelial cells.
authors.affiliation: Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06520, USA.
authors.forename: Sam X
authors.initials: SX
authors.lastname: Cheng
authors.forename: John P
authors.initials: JP
authors.lastname: Geibel
authors.forename: Steven C
authors.initials: SC
authors.lastname: Hebert
mesh_terms: D000818:Animals; D001826:Body Fluids / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space / Q000378:metabolism*; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008871:Microvilli / Q000378:metabolism; D011073:Polyamines / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D013096:Spermine / Q000008:administration & dosage
chemical_list: D011073:Polyamines; D044169:Receptors, Calcium-Sensing; D005576:Colforsin; D013096:Spermine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium