beta-Bungarotoxin-induced phospholipid hydrolysis in rat brain synaptosomes: effect of replacement of calcium by strontium.
We tested whether, upon substitution of Ca2+ by Sr2+ in a medium containing beta-bungarotoxin, sufficient Ca2+ remained bound to the tissue to support phospholipid hydrolysis in rat brain synaptosomes. The phrenic nerve--diaphragm preparation could not be used, since replacement of Ca2+ by Sr2+ prolonged time to block of indirectly evoked contractions; however, no phospholipid hydrolysis could be detected (either in the presence of Ca2+ or Sr2+), due to the small amounts of presynaptic terminals. Following initial exposure of synaptosomes to a Ca2+ containing medium and then removal of Ca2+, incubation with beta-bungarotoxin (1 or 10 micrograms/ml) caused significant phospholipid hydrolysis whether or not Sr2+ was present. Therefore, conclusions as to whether phospholipase A2 activity is required for presynaptic actions of beta-bungarotoxin cannot be derived from studies in which Sr2+ is used to inhibit enzymatic activity.
Ghassemi
A
A
Section of Pharmacology and Toxicology, University of Connecticut School of Pharmacy, Storrs 06268.
Dhillon
D S
DS
Rosenberg
P
P
D000818:Animals; D001921:Brain / Q000187:drug effects*; D002038:Bungarotoxins / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D006168:Guinea Pigs; D006868:Hydrolysis; D008297:Male; D010743:Phospholipids / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013324:Strontium / Q000494:pharmacology*; D013574:Synaptosomes / Q000187:drug effects*
D002038:Bungarotoxins; D010743:Phospholipids; D002118:Calcium; D013324:Strontium