Effects of extracellular Ca2+ and HCO3- on epidermal growth factor-induced DNA synthesis in cultured rat hepatocytes.
OBJECTIVE
The elevation of cytosolic free calcium concentration ([Ca2+]i) and intracellular pH mediate the growth factor-initiated proliferation of many cells, but it is not known if they trigger mitosis in resting hepatocytes. The maintenance of [Ca2+]i and intracellular pH depends partly on extracellular calcium concentration ([Ca2+]e) and extracellular bicarbonate concentration ([HCO3-]e). Therefore, the effects of [Ca2+]e and [HCO3-]e on hepatocyte proliferation were examined.


METHODS
Epidermal growth factor induced proliferation in primary cultures of rat hepatocytes. [3H]thymidine incorporation into DNA and nuclear labeling indices were measured.


RESULTS
Between 0.2 and 0.9 mmol/L of [Ca2+]e, the proliferative response to epidermal growth factor increased, and total hepatocellular Ca2+ content was increased. Increasing [HCO3-]e also stimulated DNA synthesis in a concentration-dependent manner, maximal at 35 mmol/L. Using optimal [Ca2+]e (0.9 mmol/L) and [HCO3-]e (35 mmol/L), a synergistic stimulation of hepatocellular DNA synthesis was shown. Voltage-dependent Ca2+ channel blockers failed to inhibit hepatocyte proliferation when administered in concentrations that inhibit proliferation in other cell types.


CONCLUSIONS
[Ca2+]e and [HCO3-]e are both essential for hepatocyte proliferation, and their effects are synergistic. The entry of extracellular Ca2+ is critical for epidermal growth factor-induced DNA synthesis in hepatocytes, but this is not mediated by voltage-dependent Ca2+ channels.
Department of Medicine, University of Sydney, Westmead Hospital, New South Wales, Australia.
B H
BH
Zhang
G C
GC
Farrell
D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis* / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051381:Rats; D017208:Rats, Wistar
D001639:Bicarbonates; D002121:Calcium Channel Blockers; D004815:Epidermal Growth Factor; D004247:DNA; D002118:Calcium