Two separate plasma membrane Ca2+ carriers participate in receptor-mediated Ca2+ influx in rat hepatocytes.
The plasma membrane Ca2+ carrier system involved in receptor-mediated Ca2+ entry was studied. Using the Ca2+ readdition protocol, the rate of cytosolic free Ca2+ concentration ([Ca2+]i) increase in vasopressin-pretreated hepatocytes was significantly higher than in thapsigargin- or 2,5-di(tert-butyl)hydroquinone-pretreated cells. The addition of Mn2+ to unstimulated hepatocytes resulted in a biphasic quench of fura-2 fluorescence. After an initial phase that was fast in rate but of short duration, the rate of fura-2 quench by Mn2+ became much slower and lasted until all the cellular fura-2 was quenched. Pretreatment of the cells with vasopressin only accelerated the rate of the latter phase but not of the initial one. In agonist-stimulated cells, acidification of the extracellular medium or the presence of ruthenium red, econazole or SK&F 96365 decreased the rates of both [Ca2+]i increase and Mn2+ entry upon addition of the respective cation. By contrast, neomycin and N-tosyl-L-phenylalanine chloromethyl ketone markedly decreased the rate of [Ca2+]i increase upon Ca2+ readdition but had no effect on vasopressin-stimulated Mn2+ entry. None of the treatments affected the ability of vasopressin and thapsigargin to mobilize the internal Ca2+ store. It is concluded that in hepatocytes the two pathways of receptor-mediated Ca2+ entry control two distinct yet pharmacologically related cation carriers.
Kass
G E
GE
Institute of Environmental Medicine, Division of Toxicology, Karolinska Institutet, Stockholm, Sweden.
Chow
S C
SC
Gahm
A
A
Webb
D L
DL
Berggren
P O
PO
Llopis
J
J
Orrenius
S
S
D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003470:Culture Media; D007093:Imidazoles / Q000494:pharmacology; D008099:Liver / Q000378:metabolism; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D010738:Type C Phospholipases / Q000378:metabolism; D014667:Vasopressins / Q000494:pharmacology
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D003470:Culture Media; D007093:Imidazoles; D011956:Receptors, Cell Surface; D013729:Terpenes; D014667:Vasopressins; D019284:Thapsigargin; D010738:Type C Phospholipases; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium