The ionophore X537A (lasolocid) transiently increases acetylcholine release from rat brain in vitro

Influences of verapamil, X-537A, A-23187 and adenosine 3',5'-cyclic monophosphate on release of 5-hydroxytryptamine from rat brain slices

Influences of verapamil, X-537A, A-23187 and cyclic-AMP on the release of [3H]-5-HT taken up into rat brain slices, were examined. Incubation with 40 mM KCl induced tritium release which was dependent on the presence of Ca2+. Verapamil, which blocks Ca2+ influx in excitable tissues, decreased potassium-induced release of 5-HT. Tritium release induced by ionophore X-537A was not dependent on extracellular Ca2+ while that induced by A-23187 required Ca2+. Cyclic-AMP, dibutyryl cyclic-AMP and theophylline did not significantly stimulate 5-HT release either in the presence or absence of Ca2+.

Stimulation of acetylcholine output from brain slices caused by the ionophores BrX-537A and A23187

1 The effect of two ionophores, BrX-537A (Bromolasolacid) and A 23187, on acetylcholine (ACh) output from brain slices was studied. 2 The slices were prepared from rat cerebral cortex, incubated in Krebs solution containing physostigmine and ACh output determined by bioassay. 3 Both ionophores enhanced ACh output. BrX-537A exerted its maximal effect, a six fold increase, at a concentration of 1.8 micron, while A 23187 caused a three fold increase at a concentration of 58 micron. 4 When the slices were incubated in a Ca-free medium, the effect of A 23187 on ACh output was only reduced, BrX-537A was abolished while that of BrX-537A was also active when disodium edetate (EDTA) was added to the the Ca-free medium. 5 The activity of BrX-537A was not affected by the presence of tetrodotoxin in the incubation medium. 6 The stimulation of ACh output elicited by KCl (25 mM) was increased further by hyoscine, but not by BrX-537A. Hyoscine however had no effect when ACh output was stimulated by BrX-537A. 7 The effect of BrX-537A on ACh output was potentiated by the addition of Mg2+ (9.3 mM) to the incubation medium and was reduced in a Mg-free medium. 8 It is concluded that A 23187 stimulates ACh output by transporting extracellular Ca2+ into cholinergic nerve endings. The effect of BrX-537A does not depend only on Ca2+ but also on other mechanisms.