Effects on the hepatocyte [Ca2+]i oscillator of inhibition of the plasma membrane Ca2+ pump by carboxyeosin or glucagon-(19-29).
Single rat hepatocytes, microinjected with the Ca(2+)-sensitive photoprotein aequorin, respond to agonists acting through the phosphoinositide signalling pathway by the generation of oscillations in cytosolic free Ca2+ concentration ([Ca2+]i). The duration of [Ca2+]i transients generated is characteristic of the receptor species activated; the variability results in differences in the rate of fall of [Ca2+]i from its peak. It is conceivable that the plasma membrane Ca(2+)-ATPase (PM Ca2+ pump) may have an important role in the mechanism underlying agonist specificity. It has recently been shown that an esterified form of carboxyeosin, an inhibitor of the red cell PM Ca2+ pump, is suitable for use in whole cell studies. Glucagon-(19-29) (mini-glucagon) inhibits the Ca2+ pump in liver plasma membranes, mediated by Gs. We show here that carboxyeosin and mini-glucagon inhibit Ca2+ efflux from populations of intact rat hepatocytes. We show that carboxyeosin and mini-glucagon enhance the frequency of oscillations induced by Ca(2+)-mobilizing agonists in single hepatocytes, but do not affect the duration of individual transients. Furthermore, we demonstrate that inhibition of the hepatocyte PM Ca2+ pump enables the continued generation of [Ca2+]i oscillations for a prolonged period following the removal of extracellular Ca2+.
Green
A K
AK
Department of Human Anatomy and Cell Biology, University of Liverpool, UK. A.K.Green@liverpool.ac.uk
Cobbold
P H
PH
Dixon
C J
CJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D004801:Eosine Yellowish-(YS) / Q000031:analogs & derivatives / Q000494:pharmacology*; D005934:Glucagon / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects*; D019284:Thapsigargin / Q000494:pharmacology
D010446:Peptide Fragments; C039265:glucagon (19-29); D019284:Thapsigargin; D005934:Glucagon; D000252:Calcium-Transporting ATPases; D002118:Calcium; D004801:Eosine Yellowish-(YS)