N-type inactivation variances in honeybee and Asian giant hornet Kv channels
Background: With the emergence of the Asian giant hornet as a threat to honeybee survival, knowledge of potential ion channel targets expressed in the nervous system can propel the development of new insecticides that are safe for pollinators. We therefore examined the biophysical properties of the Shaker-like voltage-gated potassium (Kv) channel of Apis mellifera (AmKv1; Western honeybee) and Vespa mandarinia (VmKv1; Asian giant hornet) and compared these data with isoforms that differ in N-terminal amino acid sequence.
Methods: We expressed AmKv1 and VmKv1 in Xenopus laevis oocytes and determined their gating characteristics using electrophysiological measurements. Resulting features were compared with those gleaned from N-terminal isoforms.
Results: AmKv1 generates large potassium currents, but lacks an extended N-terminal region and therefore rapid N-type inactivation, as originally described in Shaker channels. Of its seven isoforms, two have a long N-tail and subsequently display inactivation. Notably, the isoform with the lengthiest N-terminal region only partially inactivates. VmKv1 potassium currents display N-type inactivation, as expected with an extended N-tail. One isoform shows an enhanced inactivation rate, whereas currents from another isoform with a substantially different N-terminal sequence could not be measured.
Conclusion: AmKv1 and VmKv1 are functional Kv channels with strikingly different gating properties. Due to the presence of an extended N-terminal region, VmKv1 inactivates rapidly, whereas AmKv1 does not possess these residues and N-type inactivation is absent. Remarkably, virtually all isoforms of AmKv1 lack fast inactivation, whereas all studied VmKv1 isoforms inactivate, thereby suggesting a functional divergence that may be exploited for insecticide design.
Transplantation, Electrical and Electronic Engineering, Biomedical Engineering, Medicine (miscellaneous), Apis mellifera, AmKv1, Vespa mandarinia, VmKv1, N-type inactivation, Kv channel, C-TYPE INACTIVATIONION CHANNELS, POTASSIUM CHANNELS, K+ CHANNELS, VOLTAGE, TARGETS, GATE, PYRETHROIDS, MECHANISMS, INHIBITORS
Do you want to read the full article? http://dx.doi.org/10.1089/bioe.2022.0006
Neonatal Nav1.5 : pharmacological distinctiveness of a cancer‐related voltage‐gated sodium channel splice variant
Background and Purpose: Voltage-gated sodium (Na-V) channels are expressed de novo in carcinomas where their activity promotes invasiveness. Breast and colon cancer cells express the neonatal splice variant of Na(V)1.5 (nNa(V)1.5), which has several amino acid substitutions in the domain I voltage-sensor compared with its adult counterpart (aNa(V)1.5). This study aimed to determine whether nNa(V)1.5 channels could be distinguished pharmacologically from aNa(V)1.5 channels.
Experimental Approach: Cells expressing either nNa(V)1.5 or aNa(V)1.5 channels were exposed to low MW inhibitors, an antibody or natural toxins, and changes in electrophysiological parameters were measured. Stable expression in EBNA cells and transient expression in Xenopus laevis oocytes were used. Currents were recorded by whole-cell patch clamp and two-electrode voltage-clamp, respectively.
Key Results: Several clinically used blockers of Na-V channels (lidocaine, procaine, phenytoin, mexiletine, ranolazine, and riluzole) could not distinguish between nNa(V)1.5 or aNa(V)1.5 channels. However, two tarantula toxins (HaTx and ProTx-II) and a polyclonal antibody (NESOpAb) preferentially inhibited currents elicited by either nNa(V)1.5 or aNa(V)1.5 channels by binding to the spliced region of the channel. Furthermore, the amino acid residue at position 211 (aspartate in aNa(V)1.5/lysine in nNa(V)1.5), that is, the charge reversal in the spliced region of the channel, played a key role in the selectivity, especially in antibody binding.
Conclusion and Implications: We conclude that the cancer-related nNa(V)1.5 channel can be distinguished pharmacologically from its nearest neighbour, aNa(V)1.5 channels. Thus, it may be possible to design low MW compounds as antimetastatic drugs for non-toxic therapy of nNa(V)1.5-expressing carcinomas.
Pharmacology, antibody, cancer, metastasis, spider toxin, voltage-gated sodium channel, FAST INACTIVATION, LIDOCAINE BLOCK, PROSTATE-CANCER, CONCISE GUIDE, NA+ CHANNELS, IN-VITRO, EXPRESSION, NAV1.5, ACTIVATION, INVASION
Do you want to read the full article? http://dx.doi.org/10.1111/bph.15668
Homozygous SCN1B variants causing early infantile epileptic encephalopathy 52 affect voltage-gated sodium channel function
We identified nine patients from four unrelated families harboring three biallelic variants in SCN1B (NM_001037.5: c.136C>T; p.[Arg46Cys], c.178C>T; p.[Arg60Cys], and c.472G>A; p.[Val158Met]). All subjects presented with early infantile epileptic encephalopathy 52 (EIEE52), a rare, severe developmental and epileptic encephalopathy featuring infantile onset refractory seizures followed by developmental stagnation or regression. Because SCN1B influences neuronal excitability through modulation of voltage-gated sodium (Na-V) channel function, we examined the effects of human SCN1B(R46C) (beta 1(R46C)), SCN1B(R60C) (beta 1(R60C)), and SCN1B(V158M) (beta 1(V158M)) on the three predominant brain Na-V channel subtypes Na(V)1.1 (SCN1A), Na(V)1.2 (SCN2A), and Na(V)1.6 (SCN8A). We observed a shift toward more depolarizing potentials of conductance-voltage relationships (Na(V)1.2/beta 1(R46C), Na(V)1.2/beta 1(R60C), Na(V)1.6/beta 1(R46C), Na(V)1.6/beta 1(R60C), and Na(V)1.6/beta 1(V158M)) and channel availability (Na(V)1.1/beta 1(R46C), Na(V)1.1/beta 1(V158M), Na(V)1.2/beta 1(R46C), Na(V)1.2/beta 1(R60C), and Na(V)1.6/beta 1(V158M)), and detected a slower recovery from fast inactivation for Na(V)1.1/beta 1(V158M). Combined with modeling data indicating perturbation-induced structural changes in beta 1, these results suggest that the SCN1B variants reported here can disrupt normal Na-V channel function in the brain, which may contribute to EIEE52.
Do you want to read the full article? http://dx.doi.org/10.1111/epi.16913