Increased EPSCs but decreased presynaptic Ca2+ influx in S218L Cav2.1 knock-in migraine mice.

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

Washington DC, USA

Congreso; 41th Annual Meeting Society for Neuroscience; 2011

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) makes it possible to study the impact of this mutation on Ca2+-dependent neurotransmission. We studied presynaptic Ca2+ currents (IpCa) and EPSCs at the calyx of Held synapse in KI S218L mice. During voltage-clamp recordings of IpCa, a shift of the peak of the I-V curve to more negative potentials was observed in the transgenic model (WT: -10 mV, n = 10; KI: -20 mV, n = 5). Steady-state activation curves were significantly shifted in the hyperpolarizing direction (-23.0 ± 1.7 mV, n = 7 for WT vs. -36.7 ± 6.5 mV, n = 5 for KI), and IpCa activated more rapidly between -30 and +20 mV in the KI. On the other hand, presynaptic calcium currents (IpCa) evoked by action potential (AP) waveforms were smaller in KI (WT: 1.6 ± 0.2 nA, n = 9 and KI: 0.9 ± 0.2 nA, n = 5). Ca2+ current facilitation at the end of a 100 Hz train of APs was significantly reduced in KI mice (last amplitude/first amplitude*100%: 120 ± 2.5%, n = 8 for WT vs. 107 ± 2%, n = 5 for KI). Despite the decreased presynaptic Ca2+ influx, both EPSC amplitudes (KI: 8.5 ± 1.2 nA, n = 8 vs. WT: 5.5 ± 0.5 nA, n = 15) and miniature EPSC frequencies (KI: 8.6 ± 2.5 Hz vs. WT: 1.7 ± 0.3 Hz) were significantly higher in KI mice. Although the release probability was similar for both genotypes, the size of the readily-releasable pool was higher in the KI. Evoked EPSCs showed less short term depression and a faster recovery after either 10 or 100 Hz frequency trains in the KI. Our results suggest that the shift in calcium channel activation increases presynaptic calcium influx at the resting membrane potential, increasing resting cytoplasmic calcium levels. This raised calcium could mediate both the decrement in action potential-induced calcium influx, owing to calcium-dependent inactivation and enhance transmitter release.