Calcium influx mechanisms underlying calcium oscillations in rat hepatocytes.
The process of capacitative or store-operated Ca(2+) entry has been extensively investigated, and recently two major molecular players in this process have been described. Stromal interacting molecule (STIM) 1 acts as a sensor for the level of Ca(2+) stored in the endoplasmic reticulum, and Orai proteins constitute pore-forming subunits of the store-operated channels. Store-operated Ca(2+) entry is readily demonstrated with protocols that provide extensive Ca(2+) store depletion; however, the role of store-operated entry with modest and more physiological cell stimuli is less certain. Recent studies have addressed this question in cell lines; however, the role of store-operated entry during physiological activation of primary cells has not been extensively investigated, and there is little or no information on the roles of STIM and Orai proteins in primary cells. Also, the nature of the Ca(2+) influx mechanism with hormone activation of hepatocytes is controversial. Hepatocytes respond to physiological levels of glycogenolytic hormones with well-characterized intracellular Ca(2+) oscillations. In the current study, we have used both pharmacological tools and RNA interference (RNAi)-based techniques to investigate the role of store-operated channels in the maintenance of hormone-induced Ca(2+) oscillations in rat hepatocytes. Pharmacological inhibitors of store-operated channels blocked thapsigargin-induced Ca(2+) entry but only partially reduced the frequency of Ca(2+) oscillations. Similarly, RNAi knockdown of STIM1 or Orai1 substantially reduced thapsigargin-induced calcium entry, and more modestly diminished the frequency of vasopressin-induced oscillations.


CONCLUSIONS
Our findings establish that store-operated Ca(2+) entry plays a role in the maintenance of agonist-induced oscillations in primary rat hepatocytes but indicate that other agonist-induced entry mechanisms must be involved to a significant extent.
Jones
Bertina F
BF
Laboratory of Signal Transduction, National Institute of Environmental Health Sciences-NIH, Department of Health and Human Services, Research Triangle Park, NC 27709, USA.
Boyles
Rebecca R
RR
Hwang
Sung-Yong
SY
Bird
Gary S
GS
Putney
James W
JW
D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002478:Cells, Cultured; D005682:Gadolinium / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000378:metabolism; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D000071740:ORAI1 Protein; D012313:RNA / Q000494:pharmacology; D034622:RNA Interference; D051381:Rats; D017207:Rats, Sprague-Dawley; D000071737:Stromal Interaction Molecule 1; D019284:Thapsigargin / Q000494:pharmacology
D001896:Boron Compounds; D015220:Calcium Channels; D008562:Membrane Glycoproteins; D000071740:ORAI1 Protein; C532493:Orai1 protein, rat; C518857:Stim1 protein, rat; D000071737:Stromal Interaction Molecule 1; D012313:RNA; D019284:Thapsigargin; D005682:Gadolinium; C109986:2-aminoethoxydiphenyl borate; D002118:Calcium