Altered Channel Preperties And Responses To Protein Kinases Modulation In Epilepsy-associated SCN1A Mutations

Most of familial inherited generalized epilepsy with febrile seizures plus (GEFS+) are caused by missense mutations in the gene encoding the neuronal voltage-gated sodium channel subtype one (SCN1A). Biophysical properties of those mutations have been investigated in previous studies, however most mutations caused diverse effects and some resemble the wild type.We propose that some alternations may also exist in responses to the modulation by intracellular protein kinases. To test this hypothesis, I1656M and R1657C, two GEFS+associated mutations in SCN1A, were investigated in the present experiment.In the first part, biophysical properties of the mutations have been were investigated, including â… -â…¤ curve, activation, steady-state inactivation, onset of slow inactivation, slow inactivation, recovery from fast inactivation and slow inactivation. For the mutant I1656M sodium channels, only half-maximal voltage for activation and one of the time constants for recovery from slow inactivation significantly changed. For the mutant R1657C sodium channels, current density, half-maximal voltage for activation and time constants for recovery from fast inactivation and slow inactivation significantly changed.In the second part, PKA activator (forskolin) and PKC activator (PDBu) were used to investigate the responses to the modulation of the mutantations by intracellular protein kinases. For the mutant I1656M sodium channels, response of the amplitude of sodium currents to PKA activator significantly decreased, but not to PKC activator. Moreover, response of activation to PKA activator and PKC activator disappeared, while response of steady-state inactivation to PKA activator disappeared, but not to PKC activator. Response of slow inactivation to PKA activator did not change, but disappeared to PKC activator. Finally, response of the recovery from fast and slow inactivation to PKA activator also changed in some parameters, but not to PKC activator. For the mutant R1657C sodium channels, response of the amplitude of sodium currents to PKA activator significantly decreased, but not to PKC activator. Response of activation to PKA activator and PKC activator did not change, while response of steady-state inactivation to PKA activator significantly changed, but not to PKC activator. Response of slow inactivation to PKA activator and PKC activator did not change. Finally, response of the recovery from fast inactivation to PKA activator and PKC activator did not change, while response of the recovery from slow inactivation to PKA activator significantly changed, but not to PKC activator.These findings suggest that altered modulation sensitivity of the epilepsy associated SCNlA mutation channels by PKA and PKC signaling may impair the delicate balances between chemical and electrical harmony in the central nervous system, which provides a novel way to understanding the pathogenesis of inherited epilepsy and may help to pinpoint new therapeutic interventions.