Abstract
Transmembrane Ca2+-flux was studied from single isolated turtle hepatocytes by using a noninvasive Ca2+-selective self-referencing microelectrode. Cells in Ca2+-reduced culture medium demonstrated a vanadate-and lanthanum-inhibitable Ca2+-efflux of 4 x 10-17 mol Ca2+ · μm-2 · s-1 continuously over 170 h. This flux diminished with 50 nM phorbol 12-myristate 13-acetate, a protein kinase C (PKC) activator, and was reinstated on PKC deactivation with sphingosine. Progressive hypoxia resulted in a reversible suppression of Ca2+ efflux to 90% of normoxic controls with an apparent Michaelis constant for oxygen of 145 μM. PKC activation was critical in this suppression, as anaerobic administration of sphingosine caused a Ca2+ influx and cell rupture. Hypoxia was also associated with an altered pattern of adenosine-mediated control over Ca2+ efflux. Adenosine (100 μM) elevated Ca2+ efflux twofold in normoxia, but neither adenosine nor the A1-purinoreceptor antagonist 8-phenyltheophylline altered the observed anaerobic suppression. Aerobic administration of 2-10 mM KCN failed to reproduce the anaerobic suppression; however, in conjunction with 10 mM iodoacetate, complete metabolic blockade caused a Ca2+ influx and cell rupture. These observations suggest modulatory control by oxygen over transmembrane Ca2+ efflux involving second-messenger systems in the hypoxic transition.
Original language | English |
---|---|
Pages (from-to) | 776-783 |
Number of pages | 8 |
Journal | Journal of Applied Physiology |
Volume | 82 |
Issue number | 3 |
DOIs | |
Publication status | Published - 1 Mar 1997 |
Keywords
- adenosine
- calcium homeostasis
- calcium-selective
- hypometabolism
- oxygen sensing
- protein kinase C
- self-referencing probe
ASJC Scopus subject areas
- Physiology
- Physiology (medical)