RT Journal Article
SR Electronic
T1 Parvalbumin Is a Mobile Presynaptic Ca<sup>2+</sup> Buffer in the Calyx of Held that Accelerates the Decay of Ca<sup>2+</sup> and Short-Term Facilitation
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 2261
OP 2271
DO 10.1523/JNEUROSCI.5582-06.2007
VO 27
IS 9
A1 Martin Müller
A1 Felix Felmy
A1 Beat Schwaller
A1 Ralf Schneggenburger
YR 2007
UL http://www.jneurosci.org/content/27/9/2261.abstract
AB Presynaptic Ca2+ signaling plays a crucial role in short-term plasticity of synaptic transmission. Here, we studied the role of mobile endogenous presynaptic Ca2+ buffer(s) in modulating paired-pulse facilitation at a large excitatory nerve terminal in the auditory brainstem, the calyx of Held. To do so, we assessed the effect of presynaptic whole-cell recording, which should lead to the diffusional loss of endogenous mobile Ca2+ buffers, on paired-pulse facilitation and on intracellular Ca2+ concentration ([Ca2+]i) transients evoked by action potentials. In unperturbed calyces briefly preloaded with the Ca2+ indicator fura-6F, the [Ca2+]i transient decayed surprisingly fast (τfast, ∼30 ms). Presynaptic whole-cell recordings made without additional Ca2+ buffers slowed the decay kinetics of [Ca2+]i and paired-pulse facilitation (twofold to threefold), but the amplitude of the [Ca2+]i transient was changed only marginally. The fast [Ca2+]i decay was restored by adding the slow Ca2+ buffer EGTA (50–100 μm) or parvalbumin (100 μm), a Ca2+-binding protein with slow Ca2+-binding kinetics, to the presynaptic pipette solution. In contrast, the fast Ca2+ buffer fura-2 strongly reduced the amplitude of the [Ca2+]i transient and slowed its decay, suggesting that the mobile endogenous buffer in calyces of Held has slow, rather than fast, binding kinetics. In parvalbumin knock-out mice, the decay of [Ca2+]i and facilitation was slowed approximately twofold compared with wild-type mice, similar to what is observed during whole-cell recordings in rat calyces of Held. Thus, in young calyces of Held, a mobile Ca2+ buffer with slow binding kinetics, primarily represented by parvalbumin, accelerates the decay of spatially averaged [Ca2+]i and paired-pulse facilitation.