Calcium released by photolysis of DM‐nitrophen triggers transmitter release at the crayfish neuromuscular junction.

Abstract

SUMMARY1. Spontaneous and evoked transmitter release at the crayfish neuromuscular junction were potentiated in response to photolytic release of calcium from the 'caged' calcium compound DM-nitrophen, which had previously been injected into presynaptic terminals.2. The amount of calcium released from DM-nitrophen photolysis depends on the concentration of DM-nitrophen, its photoproducts, Ca2+, Mg2+, H+, ATP and the cell's native buffer. Since none of these are known in the crayfish terminal, the study was conducted in a qualitative fashion.3. Photolytic release of calcium from DM-nitrophen increased excitatory junctional potentials (EJPs) by a range of 2-31 times over control values and the miniature excitatory junctional potential (MEJP) frequency increased from resting values of 1-10 quanta/s to 3000-11000 quanta/s. 4. Extracellular calcium was not required for the light-evoked asynchronous release of transmitter. Calcium-bound DM-nitrophen previously pressure injected into crayfish presynaptic terminals increased the MEJP frequency from resting values of 1-8 quanta/s to 800-10000 quanta/s during photolysis in a calcium-free cobalt Ringer solution.5 R. M. MULKEY AND R. S. ZUCKER pulse, presumably due to the active extrusion of calcium from the presynaptic terminals.8. During photolysis of DM-nitrophen, the time courses of changes in EJP amplitude and MEJP frequency were different, indicating that the two measures of transmitter release were not linearly related.9. MEJP frequency and EJP amplitudes during DM-nitrophen photolysis were fitted to a 'non-linear summation model' in which photolytically released calcium sums with calcium entering during an action potential to evoke transmitter release with a calcium co-operativity of five.

Simultaneous Measurement of Intracellular Ca2+ and Asynchronous Transmitter Release from the same Crayfish Bouton

“…The maximal rate of asynchronous release lay between 500 and 700 s-T This value is much lower than the value of 11000 s-l obtained by Mulkey & Zucker (1993), a difference presumably explained by different recording techniques. Mulkey & Zucker (1993) recorded release from many nerve terminals innervating the same muscle fibre; we, in contrast, measured release from a single bouton.…”

“…Mulkey & Zucker (1993) recorded release from many nerve terminals innervating the same muscle fibre; we, in contrast, measured release from a single bouton. In the crayfish the excitatory terminal forms twenty to fifty synapses over a single muscle fibre (Fischer & Parnas, 1996) and so a rate of about 500-700 quanta s& for a single bouton may indicate that Mulkey & Zucker (1993) …”

Long‐term in vivo modulation of synaptic efficacy at the neuromuscular junction of Rana pipiens frogs

“…In fact, both spontaneous transmitter release and phasic release of transmitter are dependent on Ca 2+ concentration near release sites. While spontaneous release is proportional to the steady-state average intracellular Ca 2+ concentration ([Ca 2+ ] ss ) (Mulkey & Zucker, 1993;Ravin et al 1997;Angleson & Betz, 2001), evoked release is dependent on both [Ca 2+ ] ss and the changes in local Ca 2+ concentrations at the release site (Ravin et al 1999). Thus, a change in [Ca 2+ ] ss following chronic nerve stimulation could account for the observed changes in mEPP frequency and EPP amplitude.…”

“…We hypothesized that a reduction in calcium entry and/or homeostasis would result in a change in the probability of transmitter release, since there is a strong relationship between calcium entry and synaptic output (Zucker & Lara-Estrella, 1983;Augustine & Charlton, 1986;Zucker, 1996) (Mulkey & Zucker, 1993;Ravin et al 1997;Angleson & Betz, 2001), evoked release is dependent on both [Ca 2+ ] ss and the changes in local Ca 2+ concentrations at the release site (Ravin et al 1999). Thus, a change in [Ca 2+ ] ss following chronic nerve stimulation could account for the observed changes in mEPP frequency and EPP amplitude.…”

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

“…From this period on many investigators focused on the attributes of STF and LTF using the opener NMJ of crayfish to study the cellular mechanisms (Atwood, 1973(Atwood, , 1976(Atwood, , 1982Atwood et al, 1994;Zucker, 1973Zucker, , 1974a Synaptic structure to account for the differential synaptic responses can be investigated via ultrastructural analysis (Jahromi and Atwood, 1974). Measures of ionic differences due to activity is able to be investigated with axonal injections of Ca2+ and Na+ indicators as well as Ca2+ buffers (Mulkey and Zucker 1993;Winslow et al, 2002), and these fluxes can be modeled within the terminal (Winslow et al, 1994;Cooper et al, 1996b). Activity dependent adaptations Relatively recently the regional differentiation in synaptic strength and facilitation from the single motor neuron, has been addressed and appears to be due to differences from local presynaptic changes in synaptic structure and physiology Cooper, 1995, 1996a,b;Cooper et al, 1995bCooper et al, , 1996a.…”