Prolactin increases cytosolic free calcium concentration in hepatocytes of lactating rats.
PRL at a physiological concentration (10(-8) M) produced a very rapid and transient increase in 45Ca efflux in freshly isolated hepatocytes, which reached the highest value within 5 min and returned to baseline level after 20 min. PRL-induced 45Ca2+ efflux resulted in a loss of 15% of total cell calcium, which was similar to that found in vasopressin-treated cells. However, in contrast with the PRL effect, 45Ca2+ efflux induced by vasopressin was sustained. We demonstrate by using two different approaches, glycogen phosphorylase-a activation and direct cytosolic calcium concentration [( Ca2+]i) measurements, that PRL elicits a [Ca2+]i increase. The treatment of hepatic cells with PRL caused a 4-fold stimulation in glycogen phosphorylase-alpha activity after 2 min of PRL addition. Direct [Ca2+]i determination in fluo-3-loaded hepatocytes showed a 11% increase after 5 min of PRL addition. Similar data were observed in hepatocytes stimulated either with vasopressin (10(-7) M) or calcium ionophore A23187 (200 nM). The increase in [Ca2+]i promoted by PRL was independent of extracellular calcium or voltage-operated calcium channels. The data demonstrate that calcium is involved in the intracellular signaling of PRL in liver cells and that PRL initiates its action by a Ca2+ mobilization from the intracellular stores.
Villalba
M
M
Departamento de Biología Molecular, Universidad Autónoma de Madrid, Spain.
Zabala
M T
MT
Martinez-Serrano
A
A
de la Colina
R
R
Satrústegui
J
J
Garcia-Ruiz
J P
JP
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D007700:Kinetics; D007774:Lactation / Q000502:physiology*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D010762:Phosphorylase a / Q000378:metabolism; D011388:Prolactin / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013050:Spectrometry, Fluorescence
D002132:Calcium Radioisotopes; D000001:Calcimycin; D004533:Egtazic Acid; D011388:Prolactin; D010762:Phosphorylase a; D002118:Calcium