Premium
Molecular and functional characterization of the human platelet Na + /Ca 2+ exchangers
Author(s) -
Roberts Diane E,
Matsuda Toshio,
Bose Ratna
Publication year - 2012
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.2011.01600.x
Subject(s) - platelet , platelet activation , sodium calcium exchanger , chemistry , calcium , western blot , extracellular , biophysics , platelet factor 4 , cytosol , biochemistry , homeostasis , sodium–hydrogen antiporter , fura 2 , microbiology and biotechnology , sodium , medicine , endocrinology , enzyme , intracellular , heparin , biology , gene , organic chemistry
BACKGROUND AND PURPOSE The Na + /Ca 2+ exchanger is a bi‐directional transporter that plays an important role in maintaining the concentration of cytosolic Ca 2+ ([Ca 2+ ] i ) of quiescent platelets and increasing it during activation with some, but not all, agonists. There are two classes of Na + /Ca 2+ exchangers: K + ‐independent Na + /Ca 2+ exchanger (NCX) and K + ‐dependent Na + /Ca 2+ exchanger (NCKX). Platelets have previously been shown to express NCKX1. However, initial studies from our laboratory suggest that NCX may also play a role in platelet activation. The objective of this study was to determine if the human platelet expresses functional NCXs. EXPERIMENTAL APPROACH RT‐PCR, DNA sequencing and Western blot analysis were utilized to characterize the human platelet Na + /Ca 2+ exchangers. Their function during quiescence and collagen‐induced activation was determined by measuring [Ca 2+ ] i with calcium‐green/fura‐red in response to: changes in the Na + and K + gradient, NCX pharmacological inhibitors (CBDMB, KB‐R7943 and SEA0400) and antibodies specific to extracellular epitopes of the exchangers. KEY RESULTS Human platelets express NCX1.3, NCX3.2 and NCX3.4. The NCXs operate in the Ca 2+ efflux mode in resting platelets and also during their activation with thrombin but not collagen. Collagen‐induced increase in [Ca 2+ ] i was reduced with the pharmacological inhibitors of NCX (CBDMB, KB‐R7943 or SEA0400), anti‐NCX1 and anti‐NCX3. In contrast, anti‐NCKX1 enhanced the collagen‐induced increase in [Ca 2+ ] i . CONCLUSIONS AND IMPLICATIONS Human platelets express K + ‐independent Na + /Ca 2+ exchangers NCX1.3, NCX3.2 and NCX3.4. During collagen activation, NCX1 and NCX3 transiently reverse to promote Ca 2+ influx, whereas NCKX1 continues to operate in the Ca 2+ efflux mode to reduce [Ca 2+ ] i .