ATP-dependent calcium accumulation by non-mitochondrial organelles of axoplasm isolated from Myxicola giant axons.
Axoplasm from freshly isolated Myxicola giant axons was mixed with small volumes of 'artificial axoplasm' containing 45Ca and either CaEGTA/EGTA or CaDTPA/DTPA buffers giving various nominal values of [Ca2+]. The axoplasm samples were centrifuged at 100 000 X g for 30 min to form a pellet and the percentage of 45Ca bound to the pellet was determined. The fraction of bound calcium rose with increasing values of [Ca2+] along an S-shaped curve. Carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) was used to reveal the presence of mitochondrial Ca uptake. At physiological values of [Ca2+], around 100 nM, Ca uptake was insensitive to FCCP. As [Ca2+] was elevated, increasing sensitivity to FCCP was noted above [Ca2+] = 0.5 microM. At low values of [Ca2+], including the physiological range, Ca binding was significantly reduced by vanadate and quercetin, agents known to inhibit Ca uptake mediated by Ca2+-activated ATPase reactions. Inhibition of Ca binding by these agents was approximately 50% at physiological values of [Ca2+]. ATP depletion decreased the percentage of Ca binding by the pellet at physiological [Ca2+]. The results suggest that about 50% of the Ca buffering by particulate matter in axoplasm is via organelles requiring intact Ca2+-ATPase reaction at physiological values of [Ca2+].
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001369:Axons / Q000648:ultrastructure*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D008854:Microscopy, Electron; D009940:Organoids / Q000378:metabolism*; D011077:Polychaeta / Q000378:metabolism; D011794:Quercetin / Q000494:pharmacology; D014638:Vanadates; D014639:Vanadium / Q000494:pharmacology
D014639:Vanadium; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D000001:Calcimycin; D014638:Vanadates; D000255:Adenosine Triphosphate; D011794:Quercetin; D002118:Calcium