Eugenol and lidocaine inhibit voltage-gated Na+ channels from dorsal root ganglion neurons with different mechanisms.

Eugenol (EUG) is a bioactive monoterpenoid used as an analgesic, preservative, and flavoring agent. Our new data show EUG as a voltage-gated Na+ channel (VGSC) inhibitor, comparable but not identical to lidocaine (LID). EUG inhibits both total and only TTX-R voltage-activated Na+ currents (INa) recorded from VGSCs naturally expressed on dorsal root ganglion sensory neurons in rats. Inhibition is quick, fully reversible, and dose-dependent. Our biophysical and pharmacological analyses showed that EUG and LID inhibit VGSCs with different mechanisms. EUG inhibits VGSCs with a dose-response relationship characterized by a Hill coefficient of 2, while this parameter for the inhibition by LID is 1. Furthermore, in a different way from LID, EUG modified the voltage dependence of both the VGSC activation and inactivation processes and the recovery from fast inactivated states and the entry to slow inactivated states. In addition, we suggest that EUG, but not LID, interacts with VGSC pre-open-closed states, according to our data.

State-Dependent Blockade of Dorsal Root Ganglion Voltage-Gated Na+ Channels by Anethole.

Anethole is a phenolic compound synthesized by many aromatic plants. Anethole is a substance that humans can safely consume and has been studied for years as a biologically active molecule to treat a variety of conditions, including nerve damage, gastritis, inflammation, and nociception. Anethole is thought to carry out its biological activities through direct interaction with ion channels. Anethole is beneficial for neurodegenerative Alzheimer's and Parkinson's diseases. Nevertheless, nothing has been investigated regarding the effects of anethole on voltage-gated Na+ channels (VGSCs), which are major players in neuronal function. We used cultured dorsal root ganglion neurons from neonatal rats as a source of natively expressed VGSCs for electrophysiological studies using the whole-cell patch-clamp technique. Our data show that anethole interacts directly with VGSCs. Anethole quickly blocks and unblocks (when removed) voltage-activated Na+ currents in this preparation in a fully reversible manner. Anethole's binding affinity to these channels increases when the inactive states of these channels are populated, similar to lidocaine's effect on the same channels. Our data show that anethole inhibits neuronal activity by blocking VGSCs in a state-dependent manner. These findings relate to the putative anesthetic activity attributable to anethole, in addition to its potential benefit in neurodegenerative diseases.

Modulation of cardiac voltage-activated K+ currents by glypican 1 heparan sulfate proteoglycan.

BACKGROUND: Glypican 1 (Gpc1) is a heparan sulfate proteoglycan attached to the cell membrane via a glycosylphosphatidylinositol anchor, where it holds glycosaminoglycans nearby. We have recently shown that Gpc1 knockout (Gpc1-/-) mice feature decreased systemic blood pressure. To date, none has been reported regarding the role of Gpc1 on the electrical properties of the heart and specifically, in regard to a functional interaction between Gpc1 and voltage-gated K+ channels. METHODS: We used echocardiography and in vivo (electrocardiographic recordings) and in vitro (patch clamping) electrophysiology to study mechanical and electric properties of mice hearts. We used RT-PCR to probe K+ channels' gene transcription in heart tissue. RESULTS: Gpc1-/- hearts featured increased cardiac stroke volume and preserved ejection fraction. Gpc1-/- electrocardiograms showed longer QT intervals, abnormalities in the ST segment, and delayed T waves, corroborated by longer action potentials in isolated ventricular cardiomyocytes. In voltage-clamp, these cells showed decreased Ito and IK voltage-activated K+ current densities. Moreover, IK showed activation at less negative voltages, but a higher level of inactivation at a given membrane potential. Kcnh2 and Kcnq1 voltage-gated K+ channels subunits' transcripts were remarkably more abundant in heart tissues from Gpc1-/- mice, suggesting that Gpc1 may interfere in the steps between transcription and translation in these cases. CONCLUSION: Our data reveals an unprecedented connection between Gpc1 and voltage-gated K+ channels expressed in the heart and this knowledge contributes to the understanding of the role of this HSPG in cardiac function which may play a role in the development of cardiovascular disease.

Molecular basis for functional connectivity between the voltage sensor and the selectivity filter gate in Shaker K+ channels.

In Shaker K+ channels, the S4-S5 linker couples the voltage sensor (VSD) and pore domain (PD). Another coupling mechanism is revealed using two W434F-containing channels: L361R:W434F and L366H:W434F. In L361R:W434F, W434F affects the L361R VSD seen as a shallower charge-voltage (Q-V) curve that crosses the conductance-voltage (G-V) curve. In L366H:W434F, L366H relieves the W434F effect converting a non-conductive channel in a conductive one. We report a chain of residues connecting the VSD (S4) to the selectivity filter (SF) in the PD of an adjacent subunit as the molecular basis for voltage sensor selectivity filter gate (VS-SF) coupling. Single alanine substitutions in this region (L409A, S411A, S412A, or F433A) are enough to disrupt the VS-SF coupling, shown by the absence of Q-V and G-V crossing in L361R:W434F mutant and by the lack of ionic conduction in the L366H:W434F mutant. This residue chain defines a new coupling between the VSD and the PD in voltage-gated channels.

Metal Bridge in S4 Segment Supports Helix Transition in Shaker Channel.

Voltage-gated ion channels play important roles in physiological processes, especially in excitable cells, in which they shape the action potential. In S4-based voltage sensors voltage-gated channels, a common feature is shared; the transmembrane segment 4 (S4) contains positively charged residues intercalated by hydrophobic residues. Although several advances have been made in understating how S4 moves through a hydrophobic plug upon voltage changes, the possible helix transition from α- to 310-helix in S4 during the activation process is still unresolved. Here, we have mutated several hydrophobic residues from I360 to F370 in the S4 segment into histidine, in i, i + 3 and i, i + 6 or i, i + 4 and i, i + 7 pairs, to favor 310- or α-helical conformations, respectively. We have taken advantage of the ability of His to coordinate Zn2+ to promote metal ion bridges, and we have found that the histidine introduced at position 366 (L366H) can interact with the introduced histidine at position 370 (stabilizing that portion of the S4 segment in α-helical conformation). In the presence of 20 µM of Zn2+, the activation currents of L366H:F370H channels were slowed down by a factor of 3.5, and the voltage dependence is shifted by 10 mV toward depolarized potentials with no change on the deactivation time constant. Our data supports that by stabilizing a region of the S4 segment in α-helical conformation, a closed (resting or intermediate) state is stabilized rather than destabilizing the open (active) state. Taken together, our data indicates that S4 undergoes α-helical conformation to a short-lived different secondary structure transiently before reaching the active state in the activation process.

BK Channels in Cardiovascular Diseases and Aging.

Aging is a major risk factor for cardiovascular diseases, one of the main world-wide causes of death. Several structural and functional changes occur in the cardiovascular system during the aging process and the mechanisms involved in such alterations are yet to be completely described. BK channels are transmembrane proteins that play a key role in many physiological processes, including regulation of vascular tone. In vascular smooth muscle cells, BK opening and the consequent efflux of potassium (K(+)) leads to membrane hyperpolarization, which is followed by the closure of voltage-dependent Ca(2+) channels, reduction of Ca(2+) entry and vasodilatation. BK regulates nitric oxide-mediated vasodilatation and thus is crucial for normal endothelial function. Herein we will briefly review general structural properties of BK and focus on their function in the cardiovascular system emphasizing their role in cardiovascular aging and diseases.

Ileal smooth muscle motility depression on rabbit induced by toxin A from Clostridium difficile.

This study is aimed at elucidating with in vitro experiments the time course of alteration of ileal motility caused by in vivo exposure of ligated loops of ileum to toxin A (1 microg/ligated loop) of Clostridium difficile. In the sham-operated animals no significant alteration of motility was observed. In ligated loops directly injected with toxin A and in loops neighboring those administered with this toxin, a biphasic time course of motility alterations was observed. There was initially (2 h after toxin administration) an increase in spontaneous motility and in the amplitude of maximal contraction induced by potassium and acetylcholine. Afterwards there was a progressive depression of motility, which was more severe in loops directly injected. These results suggested a significant progressive depression of rabbit ileal motility induced by toxin A from C. difficile.

Crotamine inhibits preferentially fast-twitching muscles but is inactive on sodium channels.

Crotamine is a peptide toxin from the venom of the rattlesnake Crotalus durissus terrificus that induces a typical hind-limb paralysis of unknown nature. Hind limbs have a predominance of fast-twitching muscles that bear a higher density of sodium channels believed until now to be the primary target of crotamine. Hypothetically, this makes these muscles more sensitive to crotamine and would explain such hind-limb paralysis. To challenge this hypothesis, we performed concentration vs. response curves on fast (extensor digitorum longus (EDL)) and slow (soleus) muscles of adult male rats. Crotamine was tested on various human Na+ channel isoforms (Na(v)1.1-Na(v)1.6 alpha-subunits) expressed in HEK293 cells in patch-clamp experiments, as well as in acutely dissociated dorsal root ganglion (DRG) neurons. Also, the behavioral effects of crotamine intoxication were compared with those of a muscle-selective sodium channel antagonist mu-CgTx-GIIIA, and other sodium-acting toxins such as tetrodotoxin alpha- and beta-pompilidotoxins, sea anemone toxin BcIII, spider toxin Tx2-6. Results pointed out that EDL was more susceptible to crotamine than soleus under direct electrical stimulation. Surprisingly, electrophysiological experiments in human Na(v)1.1 to Na(v)1.6 Na+ channels failed to show any significant change in channel characteristics, in a clear contrast with former studies. DRG neurons did not respond to crotamine. The behavioral effects of the toxins were described in detail and showed remarkable differences. We conclude that, although differences in the physiology of fast and slow muscles may cause the typical crotamine syndrome, sodium channels are not the primary target of crotamine and therefore, the real mechanism of action of this toxin is still unknown.