Ca2+ store-dependent potentiation of Ca2+-activated non-selective cation channels in rat hippocampal neurones in vitro

1. Potentiation of calcium-activated non-selective cation (CAN) channels was studied in rat hippocampal neurones. CAN channels were activated by IP3-dependent Ca2+ release following metabotropic glutamate receptor (mGluR) stimulation either by Schaffer collateral input to CA1. neurones in brain slices in which ionotropic glutamate and GABA(A) receptors, K+ channels, and the Na+-Ca2+ exchanger were blocked or by application of the mGluR antagonist ACPD in cultured hippocampal neurones. 2. The CAN channel-dependent depolarization (Delta V-CAN) was potentiated when [Ca2+](i) was increased in neurones impaled with Ca2+-containing microelectrodes. 3. Fura-2 measurements revealed a biphasic increase in [Ca2+](i) when 200 mu M ACPD was bath applied to cultured hippocampal neurones. This increase was greatly attenuated in the presence of Cd2+. 4. Thapsigargin (1 mu M) caused marked potentiation of Delta V-CAN in CA1 neurones in the slices and of the CAN current (I-CAN) measured in whole cell-clamped cultured hippocampal neurones. 5. Ryanodine (20 mu M) also led to a potentiation of Delta V-CAN while neurones pretreated with 100 mu M dantrolene failed to show potentiation of Delta V-CAN when impaled with Ca2+-containing microelectrodes. 6. The mitochondrial oxidative phosphorylation uncoupler carbonyl cyanide m-chlorophenyl hydrazone (2 mu M) also caused a potentiation of Delta V-CAN. 7. CAN channels are subject to considerable potentiation following an increase in [Ca2+](i) due to Ca2+ release from IP3-sensitive, Ca2+-sensitive, or mitochondrial Ca2+ stores. This I-CAN potentiation may play a crucial role in the 'amplification' phase of excitotoxicity.