Direct block of cloned hKv1.5 channel by cytochalasins, actin-disrupting agents

Abstract

The action of cytochalasins, actin-disrupting agents on human Kv1.5 channel (hKv1.5) stably expressed in Ltk Ϫ cells was investigated using the whole cell patchclamp technique. Cytochalasin B inhibited hKv1.5 currents rapidly and reversibly at ϩ60 mV in a concentration-dependent manner with an IC 50 of 4.2 M. Cytochalasin A, which has a structure very similar to cytochalasin B, inhibited hKv1.5 (IC 50 of 1.4 M at ϩ60 mV). Pretreatment with other actin filament disruptors cytochalasin D and cytochalasin J, and an actin filament stabilizing agent phalloidin had no effect on the cytochalasin B-induced inhibition of hKv1.5 currents. Cytochalasin B accelerated the decay rate of inactivation for the hKv1.5 currents. Cytochalasin B-induced inhibition of the hKv1.5 channels was voltage dependent with a steep increase over the voltage range of the channel's opening. However, the inhibition exhibited voltage independence over the voltage range in which channels are fully activated. Cytochalasin B produced no significant effect on the steady-state activation or inactivation curves. The rate constants for association and dissociation of cytochalasin B were 3.7 M/s and 7.5 s Ϫ1 , respectively. Cytochalasin B produced a use-dependent inhibition of hKv1.5 current that was consistent with the slow recovery from inactivation in the presence of the drug. Cytochalasin B (10 M) also inhibited an ultrarapid delayed rectifier K ϩ current (IK,ur) in human atrial myocytes. These results indicate that cytochalasin B primarily blocks activated hKv1.5 channels and endogenous IK,ur in a cytoskeleton-independent manner as an open-channel blocker.

Use of electric cell–substrate impedance sensing to assess in vitro cytotoxicity

“…IC 50 values obtained from Var32 and VoI32 data are 0.6 μM (~ 0.3 μg/ml) and 1.3 μM (~ 0.6 μg/ml) respectively. These two IC 50 values of cytochalasin B are smaller than those obtained by MTT assay (~ 1.5–6.3 μg/ml), DNA synthesis measurement (~ 2.5 μg/ml), and whole cell patch clamp technique to measure the cytochalasin B-induced inhibition of hKv1.5 currents (~ 4.2 μM), indicating higher sensitivity for the ECIS micromotion measurement (Berger et al, 1997; Brownstein et al, 1975; Choi et al, 2005). …”

Targeting the Voltage-Dependent K+ Channels Kv1.3 and Kv1.5 as Tumor Biomarkers for Cancer Detection and Prevention

“…Finally, a number of unrelated compounds, such as CaMK II blockers (2-[N-(2-hydroxyethyl)]-N-(4methoxybenzenesulfonyl)] amino-N-(4-chlorocinnamyl)-N-methylbenzylamine; KN-93), tyrphostin (tyrosine kinase inhibitor, AG-1478), citalopram (antidepressant), disopyramide, cytochalasin (actin-disrupting agent), or loratadine (non-sedating antihistamine), also act directly on Kv1.5 [103][104][105][106][107][108]. However, their pharmacological uses targeting cell proliferation are debatable.…”

In VitroGrowth Inhibitory Effects of Cytochalasins and Derivatives in Cancer Cells

“…The latter moiety remained unaltered in 21,22-dihydrocytochalasin B (5), deoxaphomin (11), cytochalasin V (8), and cytochalasin Z3, which also shows the deoxygenation of C-20 and the hydroxylation of C-19 of the macrocyclic ring. In fact, 21,22-dihydrocytochalasin B showed the saturation of the double bond conjugated to the lactone group, which was converted into a ketone group, with deoxaphomin relating to a carboxylic [13]cytochalasin. A consistent modification of the size, functionalities, and conformational freedom of the macrocyclic ring was observed in cytochalasin V, which is a 25-oxa [15]cytochalasin showing an extended conjugated system, including a diketone, double bond and a formyl group between C(20)-C(23).…”

“…Cytochalasins have been known for decades to target the actin cytoskeleton [13,[24][25][26], which has a multitude of roles in cellular processes, including cell adhesion, motility, cellular signaling, intracellular trafficking, and cytokinesis [13,[24][25][26]. Alterations in the organization of the cytoskeleton and changes in cellular morphology, motility, and adhesiveness are characteristic features of transformed cancer cells [13,[24][25][26]. For this reason, cytoskeletal microfilaments have become promising targets for chemotherapy [13,[24][25][26].…”