Submitted on September 13, 2004
Accepted on March 25, 2005
Direct Block of Cloned hKv1.5 Channel by Cytochalasins, Actin-Disrupting Agents
Bok Hee Choi1, Jung-Ah Park1, Kyung-Ryoul Kim1, Ggot-Im Lee1, Yong-Tae Lee1, Huhn Choe2, Seong-Hoon Ko2, Min-Ho Kim3, Yeon-Ho Seo3, and Yong-Geun Kwak1*
1 Pharmacology, Chonbuk National University Medical School, Chonju, Chonbuk, Korea, Republic of
2 Anesthesiology, Chonbuk National University Medical School, Chonju, Chonbuk, Korea, Republic of
3 Thoracic and Cardiovascular Surgery, Chonbuk National University Medical School, Chonju, Chonbuk, Korea, Republic of
* To whom correspondence should be addressed. E-mail: ygkwak{at}chonbuk.ac.kr.
The action of cytochalasins, actin-disrupting agents on human Kv1.5 channel (hKv1.5) stably expressed in Ltk- cells was investigated using the whole-cell patch-clamp technique. Cytochalasin B inhibited hKv1.5 currents rapidly and reversibly at +60 mV in a concentration-dependent manner with an IC50 of 4.2 µM. Cytochalasin A, which has the very similar structure with cytochalasin B, inhibited hKv1.5 (IC50 of 1.4 µM at +60 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 channels' 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 µM-1s-1 and 7.5 s -1, 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 µM) also inhibited an ultrarapid delayed rectifier K+ current (IKur) in human atrial myocytes. These results indicate that cytochalasin B primarily blocks activated hKv1.5 channels and endogenous IKur in a cytoskeleton-independent manner as an open-channel blocker.
