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Regulation of Novel Calcium‐Sensitive Dicarboxylate Transport by the Calcium‐Sensing Receptor
Author(s) -
Walker Ryan,
ColemanBarnett Joycelynn,
Hamm Lee,
HeringSmith Kathleen
Publication year - 2015
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.29.1_supplement.809.7
Subject(s) - calcium , spermine , chemistry , calcium sensing receptor , extracellular , receptor , adenylate kinase , calcium metabolism , biophysics , biochemistry , microbiology and biotechnology , enzyme , biology , organic chemistry
Citrate inhibits calcium nephrolithiasis by complexing calcium (Ca) in a soluble form. Lowering apical extracellular Ca from 1.2mM (normal levels, Nl) to <60μM (low) results in an increase in Cit and succinate (Suc) transport in OK cells. Activation of the calcium‐sensing receptor (CaSR) with spermine inhibits transport in both low and Nl Ca. But activation of PKC with PMA inhibited transport in low Ca only, implying that Ca‐sensitive dicarboxylate transport is regulated by the CaSR through the Gq/PKC pathway. The purpose here is to determine the role of the Gi pathway. 14 C‐Suc uptakes were performed in OK cells and HRPE cells transfected with NaDC1 (CUBS). CaSRs inhibit adenylate cyclase (AC) through Gi. To mimic Gi, cells were pre‐incubated with an AC inhibitor, MDL‐12,330A (50μM for 30min) followed by uptake. The addition of MDL inhibited uptake in both Nl (0.09±0.01 to 0.05±0.01, p<0.01) and low Ca (0.13±0.01 to 0.08±0.01, p<0.01). In CUBS uptake was also inhibited in Nl (0.6±0.02 to 0.3±0.03, p<0.01) and low Ca (0.5±0.04 to 0.2±0.03, p<0.01). These results are similar to our studies of CaSR activation by spermine. If MDL inhibits transport via AC inhibition, 8‐Br‐cAMP (8‐Br) should reverse MDL action. In OK cells, MDL eliminated the Ca‐sensitivity; i.e. Nl (0.05±0.004) vs low Ca (0.05±0.002). In low Ca, 8‐Br negated the inhibitory effects of MDL thus significantly increasing uptake (0.049±0.002 to 0.063±0.002, p<0.05). Thus stimulation of the CaSR through both Gq and Gi indicates CaSR involvement in the regulation of Ca‐sensitive citrate transport. NIH/NIDDK