Calcium dependence of ryanodine‐sensitive calcium channels from brain cortex endoplasmic reticulum

Abstract

Endoplasmic reticulum vesicles isolated from rat brain cortex and fused with lipid bilayers displayed ryanodine‐sensitive calcium channels, with three cytoplasmic calcium dependences. A: Channels (n = 5) stimulated by Ca²⁺ (K _0.5 = 1.2 μM and n _Hill = 1.9) and not inhibited up to 0.5 mM Ca²⁺. B: Channels (n = 14) cooperatively activated (K _0.5 = 6.9 μM and n _Hill = 1.8), and inhibited by Ca²⁺ (K _0.5 = 152 μM and n _Hill = 1.8). C: Low P _o (< 0.1) channels (n = 22), non‐cooperatively activated and inhibited with the same K _0.5 = 26.3 μM Ca²⁺. These three types of responses to cytoplasmic [Ca²⁺] may underlie separate calcium release pathways in neurons of rat brain cortex.