Involvement of Kv1.3 and p38 MAPK signaling in HIV-1 glycoprotein 120-induced microglia neurotoxicity

Inflammatory responses mediated by activated microglia play a pivotal role in the pathogenesis of human immunodeficiency virus type 1 (HIV-1)-associated neurocognitive disorders. Studies on identification of specific targets to control microglia activation and resultant neurotoxic activity are imperative. Increasing evidence indicate that voltage-gated K⁺ (K_v) channels are involved in the regulation of microglia functionality. In this study, we investigated K_v1.3 channels in the regulation of neurotoxic activity mediated by HIV-1 glycoprotein 120 (gp120)-stimulated rat microglia. Our results showed treatment of microglia with gp120 increased the expression levels of K_v1.3 mRNA and protein. In parallel, whole-cell patch-clamp studies revealed that gp120 enhanced microglia K_v1.3 current, which was blocked by margatoxin, a K_v1.3 blocker. The association of gp120 enhancement of K_v1.3 current with microglia neurotoxicity was demonstrated by experimental results that blocking microglia K_v1.3 attenuated gp120-associated microglia production of neurotoxins and neurotoxicity. Knockdown of K_v1.3 gene by transfection of microglia with K_v1.3-siRNA abrogated gp120-associated microglia neurotoxic activity. Further investigation unraveled an involvement of p38 MAPK in gp120 enhancement of microglia K_v1.3 expression and resultant neurotoxic activity. These results suggest not only a role K_v1.3 may have in gp120-associated microglia neurotoxic activity, but also a potential target for the development of therapeutic strategies.     

Dynamics and modulation studies of human voltage gated Kv1.5 channel

The voltage gated Kv1.5 channels conduct the ultrarapid delayed rectifier current (IK_ur) and play critical role in repolarization of action potential duration. It is the most rapidly activated channel and has very little or no inactivated states. In human cardiac cells, these channels are expressed more extensively in atrial myocytes than ventricle. From the evidences of its localization and functions, Kv1.5 has been declared a selective drug target for the treatment of atrial fibrillation (AF). In this present study, we have tried to identify the rapidly activating property of Kv1.5 and studied its mode of inhibition using molecular modeling, docking, and simulation techniques. Channel in open conformation is found to be stabilized quickly within the dipalmitoylphosphatidylcholine membrane, whereas most of the secondary structure elements were lost in closed state conformation. The obvious reason behind its ultra-rapid property is possibly due to the amino acid alteration in S4–S5 linker; the replacement of Lysine by Glutamine and vice versa. The popular published drugs as well as newly identified lead molecules were able to inhibit the Kv1.5 in a very similar pattern, mainly through the nonpolar interactions, and formed sable complexes. V512 is found as the main contributor for the interaction along with the other important residues such as V505, I508, A509, V512, P513, and V516. Furthermore, two screened novel compounds show surprisingly better inhibitory potency and can be considered for the future perspective of antiarrhythmic survey.     

NaV1.2 EFL domain allosterically enhances Ca2+ binding to sites I and II of WT and pathogenic calmodulin mutants bound to the channel CTD

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Sensitivity of cloned muscle,heart and neuronal voltage-gated sodium channels to block by polyamines

Spermidine and spermine, are endogenous polyamines (PAs) that regulate cell growth and modulate the activity of numerous ion channel proteins. In particular, intracellular PAs are potent blockers of many different cation channels and are responsible for strong suppression of outward K⁺ current, a phenomenon known as inward rectification characteristic of a major class of K_IR K⁺ channels. We previously described block of heterologously expressed voltage-gated Na⁺ channels (Na_V) of rat muscle by intracellular PAs and PAs have recently been found to modulate excitability of brain neocortical neurons by blocking neuronal Na_V channels. In this study, we compared the sensitivity of four different cloned mammalian Na_V isoforms to PAs to investigate whether PA block is a common feature of Na_V channel pharmacology. We find that outward Na⁺ current of muscle (Na_V1.4), heart (Na_V1.5), and neuronal (Na_V1.2, Na_V1.7) Na_V isoforms is blocked by PAs, suggesting that PA metabolism may be linked to modulation of action potential firing in numerous excitable tissues. Interestingly, the cardiac Na_V1.5 channel is more sensitive to PA block than other isoforms. Our results also indicate that rapid binding of PAs to blocking sites in the Na_V1.4 channel is restricted to access from the cytoplasmic side of the channel, but plasma membrane transport pathways for PA uptake may contribute to long-term Na_V channel modulation. PAs may also play a role in drug interactions since spermine attenuates the use-dependent effect of the lidocaine, a typical local anesthetic and anti-arrhythmic drug.     

Channeling headache

Familial hemiplegic migraine type 1 (FMH-1) is a rare form of migraine with aura, which is characterized by transient hemiparesis, sensory loss and visual disturbances. This monogenic disease shares many common features with classic migraine, suggesting a similar molecular pathophysiology. Migraine is triggered by activation and sensitization of the trigeminovascular system, specifically the trigeminal nociceptive afferents innervating the meninges. Aura migraine is associated with cortical spreading depression (CSD), which is a short-lasting intense wave of neuronal and glial cell depolarization that slowly progresses over the cortex and is followed by long-lasting neuronal activity depression.     

Protonation state of the selectivity filter of bacterial voltage-gated sodium channels is modulated by ions

The selectivity filter (SF) of bacterial voltage-gated sodium channels consists of four glutamate residues arranged in a C₄ symmetry. The protonation state population of this tetrad is unclear. To address this question, we simulate the pore domain of bacterial voltage-gated sodium channel of Magnetococcus sp. (Na_vMs) through constant pH methodology in explicit solvent and free energy perturbation calculations. We find that at physiological pH the fully deprotonated as well as singly and doubly protonated states of the SF appear feasible, and that the calculated pKa decreases with each additional bound ion, suggesting that a decrease in the number of ions in the pore can lead to protonation of the SF. Previous molecular dynamics simulations have suggested that protonation can lead to a decrease in the conductance, but no pKa calculations were performed. We confirm a decreased ionic population of the pore with protonation, and also observe structural symmetry breaking triggered by protonation; the SF of the deprotonated channel is closest to the C₄ symmetry observed in crystal structures of the open state, while the SF of protonated states display greater levels of asymmetry which could lead to transition to the inactivated state which possesses a C₂ symmetry in the crystal structure. We speculate that the decrease in the number of ions near the mouth of the channel, due to either random fluctuations or ion depletion due to conduction, could be a self-regulatory mechanism resulting in a nonconducting state that functionally resembles inactivated states.     

Interstitial 2q24.3 deletion including SCN2A and SCN3A genes in a patient with autistic features,psychomotor delay,microcephaly and no history of seizures

Mutations in neuronal voltage-gated sodium channel genes SCN1A, SCN2A, and SCN3A may play an important role in the etiology of neurological diseases and psychiatric disorders, besides various types of epilepsy. Here we describe a 3-year-old boy with autistic features, language delay, microcephaly and no history of seizures. Array-CGH analysis revealed an interstitial deletion of ~ 291.9 kB at band 2q24.3 disrupting the entire SCN2A gene and part of SCN3A. We discuss the effects of haploinsufficiency of SCN2A and SCN3A on the genetic basis of neurodevelopmental and neurobehavioral disorders and we propose that this haploinsufficiency may be associated not only with epilepsy, but also with autistic features.