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High affinity ryanodine binding sites in rat liver endoplasmic reticulum.
1Department of Biology, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
FEBS Letters
|April 24, 1990
Summary
Liver microsomes contain ryanodine binding sites that influence calcium permeability. Ryanodine binding, inhibited by caffeine, affects calcium efflux in a concentration-dependent manner, suggesting a role in hepatic calcium regulation.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Liver microsomes are critical for cellular processes, including calcium homeostasis.
- Ryanodine is a known modulator of intracellular calcium channels.
- Understanding ryanodine interactions in hepatic tissue is essential for elucidating calcium signaling pathways.
Purpose of the Study:
- To investigate the presence and characteristics of ryanodine binding sites in rat liver microsomal subfractions.
- To determine the effect of ryanodine on calcium (Ca2+) permeability in these membranes.
- To explore the influence of caffeine on ryanodine binding.
Main Methods:
- Differential centrifugation to isolate liver microsomal subfractions.
- Radioligand binding assays using [3H]ryanodine.
- Measurement of membrane Ca2+ permeability and efflux.
Main Results:
- Smooth microsomal membranes exhibited enrichment of ryanodine binding sites and a 360 kDa polypeptide.
- Caffeine completely inhibited [3H]ryanodine binding.
- Ryanodine demonstrated a dual effect on Ca2+ permeability: stimulation of efflux at low concentrations (<10 microM) and blockade at high concentrations (>50 microM).
Conclusions:
- Hepatic microsomes possess specific ryanodine binding sites.
- These sites are capable of modulating membrane Ca2+ permeability and efflux.
- The findings suggest a role for these ryanodine-sensitive sites in hepatic calcium regulation.