High affinity ryanodine binding sites in rat liver endoplasmic reticulum

Abstract

The binding of [³H]ryanodine to liver microsomal subfractions was investigated. The smooth microsomal membranes were enriched with ryanodine binding sites and also with a polypeptide of 360 kDa. Caffeine completely inhibited [³H]ryanodine binding. Ryanodine also affected the membrane Ca²⁺ permeability. At low concentrations (< 10 μM) ryanodine stimulated Ca²⁺ efflux and at higher concentrations (> 50 μM) it blocked Ca²⁺ efflux. These results suggest that hepatic microsomes contain ryanodine binding sites which can modify the membrane permeability for Ca²⁺.