Gain of function in S218L CaV 2.1 knock-in migraine mouse model is related with resting calcium concentration [235.09/B70]

DI GUILMI MN; GONZALEZ-INCHAUSPE C; URBANO FJ; FORSYTHE ID; BORST JG; VAN DEN MAAGDENBERG AM; UCHITEL OD

New Orleans, LA, USA

Congreso; 2012 Society for Neuroscience Meeting; 2012

Society for Neuroscience

Genes encoding the P/Q-type voltage dependent Ca2+ channel CaV2.1 subunits have been linked to hereditary neurological disorders. The generation of CaV2.1 knock-in (KI) transgenic mice with the S218L familial hemiplegic migraine (FHM1) mutation (Tottene et. al. 2005) has allowed to examine physiological features of neurotransmission dependent on Ca2+ influx through a mutated channel expressed in its natural synaptic environment. We used KI S218L mice to study Ca2+ currents and excitatory postsynaptic currents (EPSCs) at the calyx of Held synapse. Whole-cell patch-clamp recordings from the KI calyx showed a strong shift of the peak of the I-V curve to more negative potentials. Steady-state activation and inactivation curves were also significantly shifted in the same direction. The window current under both curves for KI is larger and closer to the resting potential. Thus suggests that a larger population of calcium channels is readable to be activated close to the resting potential. On the other hand, presynaptic calcium currents (IpCa) evoked by action potential waveforms (APWs) were smaller in KI than in WT. Additionally, Ca2+ current facilitation after 100 or 300 Hz APW trains was significant reduced in KI compared to WT mice. In contrast, EPSC amplitudes, miniature EPSC frequencies and release probability were significant higher in KI than in WT. The EPSCs depressed less during 10 or 100 Hz trains in the KI, and recovered faster. This faster recovery from short-term synaptic depression was abolished in slices pre-incubated with EGTA-AM, suggesting an enhancement of residual calcium in KI. This hypothesis of increased presynaptic calcium was further studied with in-vivo-like stimulation patterns, yielding similar results. The present data suggest that the calcium channel activation shift increases calcium influx at resting membrane potential. Such low but continuous calcium concentration increment might lead to a decrement in action potential-induced calcium influx due to channel inactivation or a reduced expression of calcium channel in the membrane. Moreover, an increase in the presynaptic basal calcium concentration might explain the observed increment in EPSC amplitude despite a reduction in IpCa.