CALCIUM-DEPENDENCE OF RYANODINE-SENSITIVE CALCIUM CHANNELS FROM BRAINCORTEX ENDOPLASMIC-RETICULUM

Endoplasmic reticulum vesicles isolated from rat brain cortex and fuse d with lipid bilayers displayed ryanodine-sensitive calcium channels, with three cytoplasmic calcium dependences, A: Channels (n=5) stimulat ed by Ca2+ (K-0.5 = 1 2 mu M and n(Hill) = 1.9) and not inhibited up t o 0.5 miM Ca2+. B: Channels (n = 14) cooperatively activated (K-0.5 = 6.9 mu M and n(Hill) = 1.8), and inhibited by Ca2+ (K-0.5 = 152 mu M a nd n(Hill) = 1.8), C: Low P-o (< 0.1) channels (n = 22), non-cooperati vely activated and inhibited with the same K-0.5 = 26.3 mu M Ca2+. The se three types of responses to cytoplasmic [Ca2+] may underlie separat e calcium release pathways in neurons of rat brain cortex.