IFIBYNE   05513
INSTITUTO DE FISIOLOGIA, BIOLOGIA MOLECULAR Y NEUROCIENCIAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
“Characterization of acid sensing ion channels (ASICs) at the MNTB neurons in auditory brainstem slices”
Autor/es:
URBANO F.J., GONZALEZ-INCHAUSPE C., WEMMIE J., UCHITEL O.D.
Lugar:
San Diego, USA
Reunión:
Congreso; 40th Annual Meeting Society for Neuroscience; 2010
Institución organizadora:
Society for Neuroscience
Resumen:
Acid-sensing ion channels (ASICs) are a H+-gated subgroup of the degenerin/epithelial Na+ channel family of non-voltage-gated cation channels that are activated by acidification of the extracellular media. They contribute to sensory function, nociception and mechanosensation in the peripheral nervous system, and in the brain they play a role in synaptic transmission, contributing to synaptic plasticity. They are involved in ischemic stroke, fear responses, memory and learning and are also implicated in pathological conditions including ischemic stroke and multiple sclerosis. We used whole cell patch clamp recordings of neurons at the Medial Nucleus of the Trapezoid Body (MNTB) in a 0.8 mM Hepes solution at pH = 7.3 and observed that transient extracellular acidification activated ASICs, generating an inward current (IASIC). Local acidification was achieved by a 5 sec duration puff of low pH extracellular solution pressure injected with a micropipette filled with a MES (10 mM) based solution at pH = 5.5-6.3, connected to a Picrospritzer. IASIC had mean amplitudes of 2500 ± 500 pA at pH = 5.5 and 950 ± 200 pA at pH = 6.3. Mean half width was 0.66± 0.07 s, rise time 0.20 ± 0.05 s and decay times 1.45 ± 0.21 s at both pHs. The reversal potential of IASIC present at MNTB neurons was at +60 mV, suggesting that ASICs are preferentially permeable to Na+. Local application of a puff with 10 mM Hepes solution at pH = 7.3 did not activate ASICs and evoked no current. IASIC were reduced up to 85 % by external application of amiloride, a non specific inhibitor of all subunits composing ASICs. The same experiments performed in knock out mice for the ASIC1a subunit (ASIC1a -/-) generate no currents, suggesting that ASICs at the MNTB neurons from wild type mice are homomeric ASIC1a channels. These results were corroborated using Psalmotoxin which reduced IASIC by 90 % in wild type mice. ASICs desensitize during successive puffs of acid solutions and recover after 3-5 minutes of washing out at pH = 7.3 Hepes solution. ASICs at MNTB neurons were also activated by the release of H+ by iontophoresis, applying a positive electrical charge to a high resistance micropipette (20 MΩ) filled with HCl (0.1 M). IASIC evoked by this method have maximum amplitudes of 590 ± 70 pA, half width of 0.72± 0.05 s, rise time of 0.29 ± 0.05 s and decay times of 1.37 ± 0.14s. The presence of ASIC currents at MNTB neurons will allow us to study their role in synaptic transmission at the calyx of Held-MNTB synapse model.Supported by Grants from ANPCyT-FONCyT-PICT 2007-1009, 2008-2019 & PIDRI-PRH 2007 (to Dr. Urbano), Wellcome Trust, grant# 068941/Z/02/Z; PICT 6220; UBACYT; grants# X171&X223; PICT 2005-32113 & 2006-199 (to Dr. Uchitel).