[ATP1A2: a key player in familial hemiplegic migraine]

Sodium and proton effects on inward proton transport through Na/K pumps

The Na/K pump hydrolyzes ATP to export three intracellular Na (Nai) as it imports two extracellular K (Ko) across animal plasma membranes. Within the protein, two ion-binding sites (sites I and II) can reciprocally bind Na or K, but a third site (site III) exclusively binds Na in a voltage-dependent fashion. In the absence of Nao and Ko, the pump passively imports protons, generating an inward current (IH). To elucidate the mechanisms of IH, we used voltage-clamp techniques to investigate the [H]o, [Na]o, and voltage dependence of IH in Na/K pumps from ventricular myocytes and in ouabain-resistant pumps expressed in Xenopus oocytes. Lowering pHo revealed that Ho both activates IH (in a voltage-dependent manner) and inhibits it (in a voltage-independent manner) by binding to different sites. Nao effects depend on pHo; at pHo where no Ho inhibition is observed, Nao inhibits IH at all concentrations, but when applied at pHo that inhibits pump-mediated current, low [Na]o activates IH and high [Na]o inhibits it. Our results demonstrate that IH is a property inherent to Na/K pumps, not linked to the oocyte expression environment, explains differences in the characteristics of IH previously reported in the literature, and supports a model in which 1), protons leak through site III; 2), binding of two Na or two protons to sites I and II inhibits proton transport; and 3), pumps with mixed Na/proton occupancy of sites I and II remain permeable to protons.

Neuro-ophthalmologic manifestations of primary headache disorders

Headaches are the most common disorders of the central nervous system affecting 46% of the adult population worldwide. Headaches may be lifelong illnesses, often associated with substantial disability for the individual and the population as a whole. The International Classification of Headache Disorders (ICHD-II) codifies headache disorders into fourteen categories, predominantly primary headaches and secondary headache disorders. Primary headache disorders, mainly migraine and trigeminal autonomic cephalgias (TACs), are frequently associated with neuro-ophthalmologic manifestations. Ophthalmologists are often the first physicians to be involved in the deciphering of headache-related visual disturbances. This article reviews two major primary headache disorders, migraine and trigeminal autonomic cephalgias, and discusses their neuro-ophthalmic complications, clinical presentation, and treatment.

Novel mutation confirms seizure locus SCN1A is also familial hemiplegic migraine locus FHM3

Although SCN1A, the gene encoding the neuronal voltage-gated sodium channel, type 1A, is a well-recognized target of mutations underlying a spectrum of epilepsy syndromes, and lies within an extended 12-Mb disease-associated haplotype at the familial hemiplegic migraine-3 locus, it remains to be confirmed that mutations within this gene itself cause syndromes that include migraine phenotypes. The novel T1174S missense mutation of this gene was detected segregating in a family with a heterozygous female child who presented with myoclonus and an abnormal electroencephalogram, and in her heterozygous mother, who had an ataxic migraine syndrome similar to that of her own mother. This three-generation family exhibits the broad phenotypic spectrum of the dominant neuronal hyperexcitability syndromes produced by even a given allele of this sodium channel gene. It also exhibits the second allele of this sodium channel gene associated with a migraine syndrome similar to those caused at the two other familial hemiplegic migraine loci, confirming that this gene itself, not some linked gene, is the familial hemiplegic migraine-3 locus.