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Cell Signalling Biology Michael J. Berridge Module 2 Cell Signalling Pathways 2 35

Module 2: Figure temporal aspects

CALCIUM TRANSIENT

ON OFF
Reaction Reaction

Periodic stimulation Continuous stimulation

Skeletal and cardiac cell Fertilization, liver metabolism, fluid secretion,
contraction, synaptic smooth muscle contraction, cell proliferation,
transmission

Temporal aspects of Ca 2 + signalling.
In almost every example where Ca 2 + is used as a signal, it is presented as a brief transient, which is the digital signal used to set up complex temporal
patterns of Ca 2 + signalling. In some cells, these pulses are produced on demand in that they are generated in response to periodic stimulation (blue
arrows) as occurs in muscle contraction where a brief burst of Ca 2 + activates the contractile machinery, which then recovers when the Ca 2 + signal is
removed. Likewise, the release of neurotransmitters from nerve terminals is triggered by a brief localized pulse of Ca 2 + . In many other tissues, which
receive a continuous stimulation over a prolonged period (blue bar), the Ca 2 + signal is again presented as brief spikes that are produced rhythmically
to give highly regular Ca 2 + oscillations whose frequencies vary with the level of cell stimulation.

Module 2: Figure cADPR metabolism

The generation and metabolism of cyclic ADP-ribose (cADPR).
The same enzyme ADP-ribosyl cyclase is responsible for both forming and degrading cADPR. The precursor NAD + is converted into cADPR by the
cyclase activity, whereas the hydrolase component inactivates cADPR by hydrolysing it to ADP-ribose (ADPR). Reproduced from Trends Cell Biol.,
Vol. 4, Galione, A. and White, A., Ca 2 + release induced by cyclic ADP-ribose, pp. 431--436. Copyright (1994), with permission from Elsevier; see
Galione and White (1994).

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