Hypocalcemia decreases the early and late responses to epidermal growth factor in rat hepatocytes.
Extreme variations in extracellular Ca2+ concentrations ([Ca2+]e) modify the signaling generated by many hormones and growth factors. However, the influence of physiological changes in [Ca2+]e on the response to hepatic mitogens remains largely unknown. To study the influence of [Ca2+]e on the response to epidermal growth factor (EGF), hepatocytes from normal rat livers were equilibrated in vitro at [Ca2+]e similar to those observed in normocalcemia or hypocalcemia. To further investigate the effect of hypocalcemia in vivo, hepatocytes were obtained from chronically hypocalcemic rats and kept in vitro at the [Ca2+]e prevailing in vivo. Intracellular Ca2+ concentrations ([Ca2+]i) and DNA synthesis were evaluated after increasing doses of EGF. [Ca2+]e strongly influenced the [Ca2+]i response to EGF with significantly smaller [Ca2+]i increases in hepatocytes of normal rats kept in low [Ca2+]e compared with those kept in normal [Ca2+]e. In hypocalcemic rat hepatocytes, the response was further decreased and found to be significantly lower than that obtained in control cells kept in vitro at either 1.25 mmol/L or 0.8 mmol/L [Ca2+]e. In normal [Ca2+]e, the EGF-induced increases in [Ca2+]i were abolished by inhibiting EGF receptor autophosphorylation and by blocking calcium channels. Low in vitro [Ca2+]e significantly dampened the EGF-mediated DNA synthesis in normal rat hepatocytes but hypocalcemia in vivo further reduced the proliferative response compared with that obtained in control rat hepatocytes maintained in normal, or low [Ca2+]e. Furthermore, the blunted responses in [Ca2+]i mobilization and DNA synthesis associated with hypocalcemia could not be overcome by increasing concentrations of EGF nor by normalization of [Ca2+]e in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)
Bilodeau
M
M
Centre de recherche clinique André-Viallet, Hôpital Saint-Luc, Montreal, Canada.
Provencher
S J
SJ
Néron
S
S
Haddad
P
P
Vallières
S
S
Gascon-Barré
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D006996:Hypocalcemia / Q000378:metabolism*; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D004815:Epidermal Growth Factor; D004247:DNA; D007770:L-Lactate Dehydrogenase; D002118:Calcium