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Salivary Peptides Regulate Intracellular Calcium in Rat Pancreatic Beta Cells
Author(s) -
Edwards Lincoln P,
Fakhouri Walid D,
Ardestani Pegah Memar,
Zarezadeh Hossein
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1270.6
Subject(s) - calcium , calcium in biology , thapsigargin , endocrinology , intracellular , chemistry , medicine , calcium metabolism , calcium atpase , calcium signaling , microbiology and biotechnology , biochemistry , biology , atpase , enzyme
Objectives Proline Rich Proteins (PRPs), secreted by parotid gland, have a variety of functions including anti‐caries and anti‐bacterial properties, but less is known about their actions outside the oral cavity. One of these proteins, called Parotid Hormone (PH) in Sus scrofa , is believed to play a significant role in the maintenance of healthy dentin and have effects on other organs including pancreas by having regulatory effects on maintaining the sensitivity of beta cells to circulating glucose. Basic Salivary Proline Rich Protein 2 and 3 (PRB2 & PRB3), in human, have the highest sequence homology with porcine Parotid Hormone. Changes in cytosolic calcium ion concentration constitute an important element of signal transduction that may lead to insulin release. We hypothesized that PH, PRB2 and PRB3 are involved in insulin stimulation by regulating the intracellular calcium ion levels in pancreatic beta cells. Methods Cultured RIN‐m beta cells from Rattus Norvegicus were used as an in vitro model for measuring intra‐cellular calcium levels using the fluorescent dye Fura2‐AM. Cells in calcium‐rich or calcium‐free medium were treated with PH (34nmoles/200 μL), PRB2 (11nmoles/200μL) or PRB3 (11nmoles/200μL). In some experiments cells were pretreated with the L‐type calcium channel blocker diltiazem (10μM) or with thapsigargin (2μM) to deplete internal calcium stores, before treatment with the peptides. Results PH, PRB2 and PRB3 increased intracellular calcium levels in cultured beta cells by 3‐, 10‐ and 3‐fold respectively. In calcium‐free medium, no change was observed in intracellular calcium level after treatment with PH or PRB2; however treatment with PRB3 caused an increase in intracellular calcium level. Interestingly, calcium uptake by cells following PH and PRB2 treatment was partially blocked by diltiazem (10μM), whereas thapsigargin (2μM) treatment blocked the response caused by PRB3. Conclusion Salivary peptides PH, PRB2 and PRB3 show differential regulation of intracellular calcium in RIN‐m beta cells. Our data indicates that PH and PRB2 regulate an influx of external calcium partially through L‐type calcium channels, while PRB3 potentially regulates an increase of calcium from internal stores. In summary, our results suggest that PH, PRB2 and PRB3 may have regulatory functions beyond those that have been described in the literature, and may play a role in a parotid‐pancreatic axis. Support or Funding Information Departmental funding from the Department of Diagnostic and Biomedical Sciences, University of Texas Health Science Center at Houston, School of Dentistry.