Calcium Channels in Presynaptic Terminals


In vertebrates and invertebrates, neuronal communication is mediated by chemical synaptic transmission via release of transmitters that bind to receptors and result in a postsynaptic response. The release of the transmitter is mostly triggered by a transient release of intracellular calcium, brought about by activation of voltageā€gated calcium channels.

Keywords: presynaptic; ion channels; neurotransmitter; receptor; synaptic potential

Figure 1.

Synaptic transmission during voltage clamp of a presynaptic terminal. (a) to (c) Experimental data: top trace, presynaptic voltage; middle trace, postsynaptic response; lower trace, calcium current. The S‐shape of the current onset can be seen at 60 mV depolarization from a holding potential of −70 mV. Note the fast tail current and the ‘on’ and ‘off ’ (EPSP). (d) to (f) Numerical solutions to the mathematical mode: traces as in (a) to (c). C. Recorded EPSP [Ca2+]0 = 10 mmol L−1. Figure modified from Llinás .

Figure 2.

Dependence of calcium current (a) and EPSP (b) on presynaptic depolarization. (a) Solid circles, steady state ICa; open circles, tail current. (b) Solid circles, ‘on’ EPSP; crosses, ‘off ’ EPSP. The continuous curves show solutions of the mathematical model [Ca2+]0 = 10 mmol L−1. On the Pre‐V axis, 0 corresponds to a holding potential of −70 mV. Figure modified from Llinás .

Figure 3.

Synaptic delay. (a) The ‘on’ response is shown for a 60 mV presynaptic voltage clamp; 733 μs latency. (b) The ‘off ’ response is seen following a voltage clamp to the suppression potential (140 mV); 200 μs latency. (c) and (d) EPSPs generated by the mathematical model for a 60 mV clamp (‘on’ response latency, 675 μs), and a 140 mV clamp (‘off ’ response latency, 150 μs). (e) Histogram showing the variation in latency observed for the ‘on’ response (mean 0.894 ± 0.168 ms, n = 51), and the ‘off ’ response (mean 0.192 ± 0.27 ms, n = 25). Figure modified from Llinás .



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Further Reading

Kandel E et al. (2000) Principles of Neural Science. New York: McGraw‐Hill.

Katz B (1969) The release of neural transmitter substances. The Sherrington Lectures X. Springfield, IL: Charles C. Thomas.

Llinás RR (1999) The Squid Giant Synapse: A Model for Chemical Transmission. New York: Oxford University Press.

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Tsien RW, Ellinor PT and Horne WA (1991) Molecular diversity of voltage‐dependent Ca2+ channels. Trends in Pharmacological Sciences 12(9): 349–354.

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Llinás, Rodolfo R, and Moreno, Herman(May 2005) Calcium Channels in Presynaptic Terminals. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0000029]