Regulation of acetylcholine release by intracellular acidification of developing motoneurons in Xenopus cell cultures

Abstract

The effects of intracellular pH changes on the acetylcholine (ACh) release and cytoplasmic Ca2+ concentration at developing neuromuscular synapses were studied in Xenopus nerve‐muscle co‐cultures. Spontaneous and evoked ACh release of motoneurons was monitored by using whole‐cell voltage‐clamped myocytes. Intracellular alkalinization with 15 mm NH4Cl slightly reduced the frequency of spontaneous synaptic currents (SSCs). However, cytosolic acidification following withdrawal of extracellular NH4Cl caused a marked and transient increase in spontaneous ACh release. Another method of cytosolic acidification was used in which NaCl in Ringer solution was replaced with weak organic acids. The increase in spontaneous ACh release paralleled the level of intracellular acidification resulting from addition of these organic acids. Acetate and propionate but not isethionate, methylsulphate and glucuronate, caused an increase in intracellular pH and a marked increase in spontaneous ACh release. Impulse‐evoked ACh release was slightly augmented by intracellular alkalinization and inhibited by cytosolic acidification. Cytosolic acidification was accompanied by an elevation in the cytoplasmic Ca2+ concentration ([Ca2+]i), resulting from both external Ca2+ influx and intracellular Ca2+ mobilization. In contrast, the increase in [Ca2+]i induced by high K+ was inhibited by cytosolic acidification. We conclude that cytosolic acidification regulates spontaneous and evoked ACh release differentially in Xenopus motoneurons, increasing spontaneous ACh release but inhibiting evoked ACh release.

Regulation of Presynaptic NMDA Responses by External and Intracellular pH Changes at Developing Neuromuscular Synapses

“…The potentiation of SSC and an increase in intracellular free C a 2ϩ by NMDA are regulated in parallel. We found previously that a larger decrease of pH i (ϳ1.4 -1.6 pH units) is required for SSC frequency-increasing effect by weak organic acid substitution in pH e 6.6 Ringer's solution (Chen et al, 1998). In the current study, the intracellular fluid revealed an acidific shift in pH of only 0.2-0.4 units by weak organic acid substitution in normal Ringer's solution.…”

The Na+/H+ exchanger is a major pH regulator in GABAergic presynaptic nerve terminals synapsing onto rat CA3 pyramidal neurons

“…The effect of pH i on GABAergic mIPSCs was examined using the ammonium prepulse technique. External NH 4 Cl application is expected to alkalinize the environment within presynaptic nerve terminals during its application, but to acidify after its removal (Roos and Boron 1981; Chen et al . 1998a).…”

“…We also investigated the effect on mIPSCs of directly acidifying the terminal with the external application of a weak organic acid. Na‐propionate is expected to acidify presynaptic nerve terminals during its application, but to alkalinize after its removal (Roos and Boron 1981; Chen et al . 1998a).…”

“…1998b; Bonnet and Wiemann 1999; Kiss and Korn 1999). In presynaptic nerve terminals, changes in pH i also have been reported to regulate neurotransmitter release (Nachshen and Drapeau 1988; Chen et al . 1998a; Trudeau et al .…”

Reversal of Memory Deficits by Atorvastatin and Simvastatin in Rats

“…48) The increased free intracellular Ca 2＋ is known to increase the release of acetylcholine from nerve terminals. 60) Moreover increased intracellular Ca 2＋ increases cAMP levels, which subsequently activates PKA. 61) Therefore, reversal of Scopolamine induced amnesia by Atorvastatin and Simvastatin may be due to the activation of PI3K/Akt pathway.…”