Simulation of the effect of an external GHz electric field on the potential energy profile of Ca2+ ions in the selectivity filter of the CaV Ab channel.

CaV channels are transmembrane proteins that mediate and regulate ion fluxes across cell membranes, and they are activated in response to action potentials to allow Ca2+ influx. Since ion channels are composed of charge or polar groups, an external alternating electric field may affect the ion-selective membrane transport and the performance of the channel. In this article, we have investigated the effect of an external GHz electric field on the dynamics of calcium ions in the selectivity filter of the CaV Ab channel. Molecular dynamics (MD) simulations and the potential of mean force (PMF) calculations were carried out, via the umbrella sampling method, to determine the free energy profile of Ca2+ ions in the CaV Ab channels in presence and absence of an external field. Exposing CaV Ab channel to 1, 2, 3, 4, and 5 GHz electric fields increases the depth of the potential energy well and this may result in an increase in the affinity and strength of Ca2+ ions to binding sites in the selectivity filter the channel. This increase of strength of Ca2+ ions binding in the selectivity filter may interrupt the mechanism of Ca2+ ion conduction, and leads to a reduction of Ca2+ ion permeation through the CaV Ab channel.

Smart bomb AS1411 aptamer-functionalized/PAMAM dendrimer nanocarriers for targeted drug delivery in the treatment of gastric cancer.

Chemotherapy, a conventional method assessed in recent oncology studies, poses numerous problems in the clinical environment. To overcome the problems inherent in chemotherapy, an intelligent drug delivery system has come to the forefront of cancer therapeutics. In this study, we designed a dendrimer-based pharmaceutical system together with a single-stranded AS1411 aptamer (APTAS1411 ) as a therapeutic strategy. The polyamidoamine (PAMAM)-polyethylene glycol (PEG) complex was then conjugated with the AS1411 aptamer and confirmed by atomic-force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) .In this study, we show that the conjugated PAMAM-PEG-APTAS1411 complex dramatically increased PAMAM-PEG-5-FU uptake by MKN45 gastric cancer cells. We also demonstrated both the stability of the nanoparticle-5-FU-APTAS1411 complex, by thin layer chromatography (TLC), and an increase in 5-fluorouracil (5-FU) accumulation in the vicinity of cancerous tumors. This smart drug delivery system is capable of effectively transferring 5-FU to MKN45 gastric cancer cells in consistent and without toxic effects.

Modeling ion permeation through a bacterial voltage-gated calcium channel CaVAb using molecular dynamics simulations.

Activation of voltage-gated calcium channels by action potentials leads to the influx of Ca2+ ions. In this study, the ion permeation characteristics in bacterial voltage-gated calcium (CaVAb) channels were investigated using molecular dynamics simulations. Furthermore, the potential of mean force (PMF) calculations was evaluated to determine the free energy profile for the permeation of cations (Ca2+ and Na+) and anions (Cl-) in the CaVAb channel. The results showed that both Ca2+ and Na+ cations experienced a deep energy well, while the Cl- anion experienced a relatively high energy barrier at the center of the selectivity filter (site 2). Consistent with the experimental data, the results obtained from this study demonstrate that sites 2 and 3 displayed the highest and lowest affinities to Ca2+, respectively. These findings also indicate that Na+ can easily and quickly pass through the CaVAb channel in the absence of Ca2+, while Cl- ions lack this ability.