The inhibitory effect of the toxic fraction from sea urchin (Toxopneustes pileolus) venom on 45Ca2+ uptake in crude synaptosome fraction from chick brain.
The effects of toxic peaks (P-I, P-II and P-III eluted from Sephadex G-200 column) from the sea urchin Toxopneustes pileolus on time-dependent 45Ca2+ uptake in chick P2 fraction (crude synaptosome fraction) were studied under physiological ionic conditions. Time-dependent 45Ca2+ uptake was inhibited by P-II and P-III, but not by P-I. P-II had the greatest inhibitory effect. The inhibitory effect of P-II was not due to the inhibition of 45Ca2+ binding on P2 fraction, because P-II did not affect 45Ca2+ binding in osmotic-shocked P2 fraction. P-II did not affect KCl-stimulated 45Ca2+ uptake in P2 fraction, (Ca(2+)-Mg2+)-ATPase activity in the synaptic plasma membrane (SPM) fraction, or (Na(+)-K+)-ATPase and Mg(2+)-ATPase activities in osmotically-shocked P2 fraction. In contrast, the Na+/Ca2+ exchanger blocker 2',4'-dichlorobenzamil (DCB; 100 microM), with a poor specificity, inhibited not only time-dependent 45Ca2+ uptake but also KCl-stimulated 45Ca2+ uptake, (Ca(2+)-Mg2+)-ATPase, Mg(2+)-ATPase and (Na(+)-K+)-ATPase. Involvement of Na(+)-Ca2+ exchanger in the time-dependent 45Ca2+ uptake was ruled out, since it was not inhibited by replacement of Na+ with Li+ in reaction medium. These results suggested that the inhibition by P-II on time-dependent 45Ca2+ uptake appeared to be more specific than the commercially available Na+/Ca2+ exchanger blocker DCB, although the mechanism is not clear yet.
Zhang
Y A
YA
Department of Biological Chemistry, Faculty of Pharmaceutical Sciences, Kinki University, Osaka, Japan.
Wada
T
T
Iwasaki
Y
Y
Nakagawa
H
H
Ichida
S
S
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002645:Chickens; D012617:Sea Urchins / Q000737:chemistry*; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D014688:Venoms / Q000302:isolation & purification / Q000633:toxicity*
D015220:Calcium Channels; D019831:Sodium-Calcium Exchanger; D014688:Venoms; D000252:Calcium-Transporting ATPases; D002118:Calcium