title: L-histidine sensing by calcium sensing receptor inhibits voltage-dependent calcium channel activity and insulin secretion in β-cells.
abstract: OBJECTIVE
  Our goal was to test the hypothesis that the histidine-induced activation of calcium sensing receptor (CaR) can regulate calcium channel activity of L-type voltage dependent calcium channel (VDCC) due to increased spatial interaction between CaR and VDCC in β-cells and thus modulate glucose-induced insulin secretion.
  
  
  METHODS
  Rat insulinoma (RINr1046-38) insulin-producing β-cells were cultured in RPMI-1640 medium on 25 mm diameter glass coverslips in six-well culture plates in a 5% CO(2) incubator at 37°C. The intracellular calcium concentration, [Ca(2+)](i), was determined by ratio fluorescence microscopy using Fura-2AM. The spatial interactions between CaR and L-type VDCC in β-cells were measured by immunofluorescence confocal microscopy using a Nikon C1 laser scanning confocal microscope. The insulin release was determined by enzyme-linked immunosorbent assay (ELISA).
  
  
  RESULTS
  The addition of increasing concentrations of L-histidine along with 10 mM glucose resulted in 57% decrease in [Ca(2+)](i). The confocal fluorescence imaging data showed 5.59 to 8.62-fold increase in colocalization correlation coefficient between CaR and VDCC in β-cells exposed to L-histidine thereby indicating increased membrane delimited spatial interactions between these two membrane proteins. The insulin ELISA data showed 54% decrease in the 1st phase of glucose-induced insulin secretion in β-cells exposed to increasing concentrations of L-histidine.
  
  
  CONCLUSIONS
  L-histidine-induced increased spatial interaction of CaR with VDCC can inhibit calcium channel activity of VDCC and consequently regulate glucose-induced insulin secretion by β-cells. The L-type VDCC could therefore be a potential therapeutic target in diabetes.
authors.affiliation: Robert Stempel College of Public Health and Social Work, Department of Environmental and Occupational Health, Florida International University, 11200 SW 8th Street, HLS-594, Miami, FL 33199, USA. parkashj@fiu.edu
authors.forename: Jai
authors.initials: J
authors.lastname: Parkash
authors.forename: Kamlesh
authors.initials: K
authors.lastname: Asotra
mesh_terms: D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006639:Histidine / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D007340:Insulinoma / Q000473:pathology; D018613:Microscopy, Confocal; D051381:Rats; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D020746:Calcium Channels, L-Type; D007328:Insulin; D044169:Receptors, Calcium-Sensing; D006639:Histidine; D005947:Glucose