Chronic Ca2+ influx through voltage-dependent Ca2+ channels enhance delayed rectifier K+ currents via activating Src family tyrosine kinase in rat hippocampal neurons

Excessive influx and the subsequent rapid cytosolic elevation of Ca2+ in neurons is the major cause to induce hyperexcitability and irreversible cell damage although it is an essential ion for cellular signalings. Therefore, most neurons exhibit several cellular mechanisms to homeostatically regulate cytosolic Ca2+ level in normal as well as pathological conditions. Delayed rectifier K+ channels (IDR channels) play a role to suppress membrane excitability by inducing K+ outflow in various conditions, indicating their potential role in preventing pathogenic conditions and cell damage under Ca2+-mediated excitotoxic conditions. In the present study, we electrophysiologically evaluated the response of IDR channels to hyperexcitable conditions induced by high Ca2+ pretreatment (3.6 mM, for 24 hours) in cultured hippocampal neurons. In results, high Ca2+-treatment significantly increased the amplitude of IDR without changes of gating kinetics. Nimodipine but not APV blocked Ca2+-induced IDR enhancement, confirming that the change of IDR might be targeted by Ca2+ influx through voltage-dependent Ca2+ channels (VDCCs) rather than NMDA receptors (NMDARs). The VDCC-mediated IDR enhancement was not affected by either Ca2+-induced Ca2+ release (CICR) or small conductance Ca2+-activated K+ channels (SK channels). Furthermore, PP2 but not H89 completely abolished IDR enhancement under high Ca2+ condition, indicating that the activation of Src family tyrosine kinases (SFKs) is required for Ca2+-mediated IDR enhancement. Thus, SFKs may be sensitive to excessive Ca2+ influx through VDCCs and enhance IDR to activate a neuroprotective mechanism against Ca2+-mediated hyperexcitability in neurons.