INVESTIGADORES
KATZ Eleonora
congresos y reuniones científicas
Título:
The Calcium Dependence of ACHRs in Avian (Gallus) Hair Cells
Autor/es:
GI JUNG IM; MARCELA LIPOVSEK; ELEONORA KATZ; ANA BELÉN ELGOYHEN; PAUL A FUCHS
Lugar:
Baltimore
Reunión:
Congreso; 34th Midwinter Meeting of the Association for Research in Otolaryngology; 2011
Resumen:
From birth until
the onset of hearing (postnatal day (P) 12),
IHCs are transiently innervated by cholinergic medial olivocochlear (MOC)
fibers. At this synapse, transmitter release is supported by both N- and
P/Q-type voltage-gated calcium channels (VGCCs) (Zorrilla de San Martín et al.,
J. Neurosci 2010). The fast formation and retraction of the MOC-IHC synapse
suggest there may also be associated changes in synaptic transmission throughout this period. Short
term plasticity (STP) is a dynamic process that depends on the balance between
facilitation and depression of synaptic responses caused by preceding activity.
Our goal is to determine whether there are changes in STP at
the MOC-IHC synapse during development and, if so, to understand the mechanisms
underlying them. Synaptic activity was recorded in voltage-clamped IHCs from
excised apical turns of the mouse cochlea at two developmental stages (P5-7 and
P9-11) during electrical stimulation of the MOC fibers. Ten-pulse trains at 10,
20, 40 and 100 Hz applied to P5-7 MOC-IHC synapses led to 1.8±0.3; 1.7±0.2;
1.8±0.3 and 2±0.4-fold increase in synaptic efficacy, respectively, estimated
as the ratio between the mean amplitude of the fifth and the first evoked
synaptic current (S5/S1); n=7-10. The same protocols
applied to P9-11 synapses led to a progressive decrease of the S5/S1
value (0.8±0.1; 0.7±0.1; 0.6±0.1; 0.4±0.1 for the 10, 20, 40 and 100 Hz trains,
respectively; n=12-18). Depression upon high frequency stimulation at P9-11 was
reversed to facilitation when reducing quantal output either by decreasing [Ca2+]o
or by blocking P/Q-type VGCCs with w-Agatoxin IVA (200 nM). Our results show there is a
developmental switch from facilitation to depression upon high frequency
stimulation consistent with the increment in the probability of release. We are
now studying whether these changes in synaptic transmission can be accounted
for by differences in the coupling between calcium influx and transmitter
release.