The human voltage gated potassium channel Kv1.5 that conducts the I_Kur current is a key determinant of the atrial action potential. Its mutations have been linked to hereditary forms of atrial fibrillation (AF), and the channel is an attractive target for the management of AF. The development of I_Kur blockers to treat AF resulted in small molecule Kv1.5 inhibitors. The selectivity of the blocker for the target channel plays an important role in the potential therapeutic application of the drug candidate: the higher the selectivity, the lower the risk of side effects. In this respect, small molecule inhibitors of Kv1.5 are compromised due to their limited selectivity. A wide range of peptide toxins from venomous animals are targeting ion channels, including mammalian channels. These peptides usually have a much larger interacting surface with the ion channel compared to small molecule inhibitors and thus, generally confer higher selectivity to the peptide blockers. We found two peptides in the literature, which inhibited I_Kur: Ts6 and Osu1. Their affinity and selectivity for Kv1.5 can be improved by rational drug design in which their amino acid sequences could be modified in a targeted way guided by in silico docking experiments.

5-chloro-2-guanidinobenzimidazole (ClGBI), a small-molecule guanidine derivative, is a known effective inhibitor of the voltage-gated proton (H⁺) channel (H_V1, K_d ≈ 26 μM) and is widely used both in ion channel research and functional biological assays. However, a comprehensive study of its ion channel selectivity determined by electrophysiological methods has not been published yet. The lack of selectivity may lead to incorrect conclusions regarding the role of hHv1 in physiological or pathophysiological responses in vitro and in vivo. We have found that ClGBI inhibits the proliferation of lymphocytes, which absolutely requires the functioning of the K_V1.3 channel. We, therefore, tested ClGBI directly on hK_V1.3 using a whole-cell patch clamp and found an inhibitory effect similar in magnitude to that seen on hH_V1 (K_d ≈ 72 μM). We then further investigated ClGBI selectivity on the hK_V1.1, hK_V1.4-IR, hK_V1.5, hK_V10.1, hK_V11.1, hK_Ca3.1, hNa_V1.4, and hNa_V1.5 channels. Our results show that, besides H_V1 and K_V1.3, all other off-target channels were inhibited by ClGBI, with K_d values ranging from 12 to 894 μM. Based on our comprehensive data, ClGBI has to be considered a non-selective hH_V1 inhibitor; thus, experiments aiming at elucidating the significance of these channels in physiological responses have to be carefully evaluated.

Rheumatoid arthritis (RA) is one of the most prevalent autoimmune diseases. Its therapy is often challenging, even in the era of biologicals. Previously, we observed the anti-inflammatory effects of garlic-derived organic polysulfide dimethyl trisulfide (DMTS). Some of these effects were mediated by activation of the TRPA1 ion channel. TRPA1 was mostly expressed in a subset of nociceptor neurons. We decided to investigate the action of DMTS in K/BxN serum-transfer arthritis, which is a relevant model of RA. TRPA1 gene knockout (KO) and wild-type (WT) mice were used. The interaction of DMTS and TRPA1 was examined using a patch clamp in CHO cells. Arthritis was characterized by mechanical hyperalgesia, paw swelling, movement range of the ankle joint, hanging performance, plasma extravasation rate, myeloperoxidase activity, and histological changes in the tibiotarsal joint. DMTS activated TRPA1 channels dose-dependently. DMTS treatment reduced paw swelling and plasma extravasation in both TRPA1 WT and KO animals. DMTS-treated TRPA1 KO animals developed milder collagen deposition in the inflamed joints than WT ones. TRPA1 WT mice did not exhibit significant cartilage damage compared to ones administered a vehicle. We concluded that DMTS and related substances might evolve into novel complementary therapeutic aids for RA patients.

B cells express various ion channels, but the presence of voltage-gated sodium (Na_V) channels has not been confirmed in the plasma membrane yet. In this study, we have identified several Na_V channels, which are expressed in the human B cell membrane, by electrophysiological and molecular biology methods. The sensitivity of the detected sodium current to tetrodotoxin was between the values published for TTX-sensitive and TTX-insensitive channels, which suggests the co-existence of multiple Na_V1 subtypes in the B cell membrane. This was confirmed by RT-qPCR results, which showed high expression of TTX-sensitive channels along with the lower expression of TTX-insensitive Na_V1 channels. The biophysical characteristics of the currents also supported the expression of multiple Na_V channels. In addition, we investigated the potential functional role of Na_V channels by membrane potential measurements. Removal of Na⁺ from the extracellular solution caused a reversible hyperpolarization, supporting the role of Na_V channels in shaping and maintaining the resting membrane potential. As this study was mainly limited to electrophysiological properties, we cannot exclude the possible non-canonical functions of these channels. This work concludes that the presence of voltage-gated sodium channels in the plasma membrane of human B cells should be recognized and accounted for in the future.

ABT-333 (dasabuvir) is an antiviral agent used in hepatitis C treatment. The molecule, similarly to some inhibitors of hERG channels, responsible for the delayed rectifier potassium current (I_Kr), contains the methanesulfonamide group. Reduced I_Kr current leads to long QT syndrome and early afterdepolarizations (EADs), therefore potentially causing life-threatening arrhythmias and sudden cardiac death. Our goal was to investigate the acute effects of ABT-333 in enzymatically isolated canine left ventricular myocardial cells. Action potentials (APs) and ion currents were recorded with a sharp microelectrode technique and whole-cell patch clamp, respectively. Application of 1 μM ABT-333 prolonged the AP in a reversible manner. The maximal rates of phases 0 and 1 were irreversibly decreased. Higher ABT-333 concentrations caused larger AP prolongation, elevation of the early plateau potential, and reduction of maximal rates of phases 0, 1, and 3. EADs occurred in some cells in 3–30 μM ABT-333 concentrations. The 10 μM ABT-333-sensitive current, recorded with AP voltage clamp, contained a late outward component corresponding to I_Kr and an early outward one corresponding to transient outward potassium current (I_to). ABT-333 reduced hERG-channel-mediated ion current in a concentration-dependent, partially reversible manner with a half-inhibitory concentration of 3.2 μM. As the therapeutic plasma concentration of ABT-333 can reach the low μM range, ABT-333 application carries a risk of cardiac side effects especially in case of coadministration with strong inhibitors of CYP2C8.

Delavirdine is an anti-HIV agent with structural similarity (presence of methanesulfonamide group) to well-known rapid delayed rectifier potassium current (I_Kr) inhibitors like dofetilide and E-4031. In spite of this and the fact, that I_Kr blockade can lead to long QT syndrome with a risk of early afterdepolarization, cardiac arrhythmia and even sudden cardiac death development, there is no information on the cardiac electrophysiological effects of the delavirdine. Therefore, we examined the concentration-dependent acute effects of delavirdine on action potential morphology and on the underlying ion currents in enzymatically dispersed canine ventricular cardiomyocytes, as well as in a hERG-channel- and NaV1.5-expressing cell lines. Delavirdine application in the µM concentration range resulted in rapid, potent and reversible blockade of expressed hERG channels. NaV1.5 channels were slightly reduced by delavirdine. Moreover, APD increase, reduction of maximal rates of phases 1 and 3 and a small increase of Plateau20 amplitude were detected in canine left ventricular isolated cardiomyocytes in a concentration-dependent manner. Accordingly, the delavirdine-sensitive current contained an early and transient, as well as a late outward component corresponding to phases 1 and 3 of the AP. These results support the delavirdine-evoked inhibition of I_Kr, transient outward potassium current as well as sodium current. As these concentrations are similar to therapeutic plasma values (7-30 µM), delavirdine application might carry some risk of cardiac side effects especially in HIV-infected patients with altered cardiac function or patients with co-administration of drugs metabolized by certain cytochrome P450 isoforms.