Different mechanisms of Ca²⁺ regulation that influence synaptic transmission: Comparison between crayfish and Drosophila neuromuscular junctions

Abstract

A brief historical background on synaptic transmission in relation to Ca(2+) dynamics and short-term facilitation is described. This study focuses on the mechanisms responsible for the regulation of intracellular calcium concentration ([Ca(2+)](i)) in high output terminals of larval Drosophila compared to a low-output terminal of the crayfish neuromuscular junction (NMJ). Three processes; plasmalemmal Na(+)/Ca(2+) exchanger [NCX], Ca(2+)-ATPase (PMCA), and sarcoplasmic/endoplasmic Ca(2+)-ATPase (SERCA) are important in regulating the [Ca(2+)](i) are examined. When the NCX is compromised by reduced [Na(+)](o), no consistent effect occurred; but a NCX blocker KB-R7943 decreased the excitatory postsynaptic potential (EPSP) amplitudes. Compromising the PMCA with pH 8.8 resulted in an increase in EPSP amplitude but treatment with a PMCA specific inhibitor carboxyeosin produced opposite results. Thapsigargin exposure to block the SERCA generally decreases EPSP amplitude. Compromising the activity of the above Ca(2+) regulating proteins had no substantial effects on short-term depression. The Kum(170TS) strain (with dysfunctional SERCA), showed a decrease in EPSP amplitudes including the first EPSP within the train. Synaptic transmission is altered by reducing the function of the above three [Ca(2+)](i) regulators; but they are not consistent among different species as expected. Results in crayfish NMJ were more consistent with expected results as compared to the Drosophila NMJ. It is predicated that different mechanisms are used for regulating the [Ca(2+)](i) in high and low output synaptic terminals.

Roles of the Sarcoplasmic/Endoplasmic Reticulum Ca2+-ATPase, Plasma Membrane Ca2+-ATPase and Na+/Ca2+ Exchanger in Regulation of Heart Rate in Larval Drosophila~!2010-03-10~!2010-08-13~!2010-08-27~!

“…As specific ionic current recordings are forth coming in myocytes, it is hopeful that the cellular responses of inhibiting NCX, SERCA and PMCA can be determined. A similar investigation in the function of these three proteins has just been reported on in relation to synaptic transmission at skeletal neuromuscular junctions in Drosophila and crayfish [84]. Diseases that inflict humans are becoming more common to be genetically modeled in Drosophila melanogaster [1][2][3][4][5][6], and thus the physiological alterations continually need to be assessed.…”

Drosophila rugoseIs a Functional Homolog of MammalianNeurobeachinand Affects Synaptic Architecture, Brain Morphology, and Associative Learning

“…To address this issue, we quantified synaptic bouton numbers at the NMJ of third-instar larvae, a standard preparation used for investigating structural and functional aspects of synaptic function (Desai-Shah and Cooper, 2009). After anti-HRP staining, both, rg FDD and rg 1 hemizygous male larvae showed increased bouton numbers per muscle area compared with w 1118 and wild-type Canton-S controls (Fig.…”

Historical View and Physiology Demonstration at the NMJ of the Crayfish Opener Muscle

“…The frequency of stimulation within the train can be varied (40,60 and 80 Hz). Intracellular EPSP recordings are routinely performed by these standard procedures (Crider & Cooper, 1999Cooper et al 1995b;Dudel, 1983;Desai-Shah and Cooper, 2009). …”