Page 45 - F. Cell biology

Cinnarizine Inhibits Human Kv1.5 Channel

Currents in the Open state

Soobeen Hwang , Su-Hyun Jo 1,2
1

1 Interdisciplinary Graduate Program for BIT Medical Convergence, Kangwon National University, Chuncheon 200-701, Korea

2 Department of Physiology, School of Medicine, Kangwon National University, Chuncheon 200-701, Korea

ABSTRACT A A A

1.1 1.1
Cinnarizine is an antagonist of several vasoactive 1.1 200µM Cinnarizine

drugs including adrenaline, angiotensin and 5- 1.0 1.0

hydroxytryptamine. Cinnarizine used in the treatment 1.0 0.9 0.9

of vestibular dysfunction, migraine, cerebral, or Normalized peak current 0.8 Normalized steady-state current

peripheral vascular insufficiency with rare major 0.9 0.8

adverse effect. The Kv1.5 channel is a shaker-type, Wash out 0.7 1 s 0.7 1 s
5 s
5 s
voltage-gated potassium channel encoded by the Normalized peak current 0.8 0.6 0 100 200 300 400 0.6

KCNA5 gene. It contributes to the maintenance of Time after drug addition (s) 0 100 200 300 400

cell membrane potential in a wide variety of tissues, 0.7 control Time after drug addition (s)
Control
including myocytes, pancreatic β-cells, neurons, and cell3 B B
200µM Cinnarizine

smooth muscle cells in the pulmonary vasculature. 1.1 1.1

We examined the effect of cinnarizine on the human 0.6 0 20 40 60 80 100 120 1.0

Kv1.5 channel using a Xenopus oocyte expression Time (min) 1.0

system and a two-microelectrode voltage clamp 0.9 0.9

technique. Cinnarizine reduced the amplitude of the B Normalized peak current 0.8 Normalized steady-state current 0.8

Kv1.5 channel current in a concentration-dependent 1 s 1 s

5 s
manner. Cinnarizine rapidly inhibited Kv1.5 currents 0.7 0.7 5 s

in 6 min, eliminating the possibility of genomic 1.1 200µM Cinnarizine 0.6 0 20 40 60 80 0.6 0 20 40 60 80

regulation. Inhibition rate for cinnarizine on Kv1.5 Number of test pulses Number of test pulses

channel was dependent on the degree of 1.0 C C

concentration. Inhibition rates for peak and steady

state currents were not significantly different at all 0.9

voltage we examined. These results suggested that 12 12

cinnarizine inhibited Kv1.5 currents via a non- Normalized steady-state current 0.8 8 8

genomic mechanism, providing a mechanism for the Wash out 4 4

arrhythmogenic effects of cinnarizine. control Peak current blockade (%) 0 Steady-state current blockade (%) 0
Control
0.7 cell3 -4 1 s
200µM Cinnarizine

15 s -4 1 s
15 s
-8 -8
0.6 0 20 40 60 80 100 0 20 40 60 80 100

KEY WORDS 0 20 40 60 80 100 120 Number of test pulses Number of test pulses

Time (min)

Cinnarizine; Kv1.5 channel; Non-genomic; Figure 3. Use- Figure 4. Use-

Potassium channel
Figure 2. Reversible inhibitions of Kv1.5 dependency of Kv1.5 dependency of Kv1.5

channels by cinnarizine. (A,B) Peak current and peak currents blockage steady-state currents

steady-state current recordings before and after by cinnarizine. (A) One- blockage by cinnarizine.

washing out 200 μM cinnarizine. Currents were hundred sixty and eighty (A) One-hundred sixty and

evoked by a 200-ms depolarizing pulse to +30 mV repeated 200 ms +50 mV eighty repeated 200 ms

from a holding potential of −60 mV at 20-s intervals. depolarization pulses from +50 mV depolarization

Normalized peak currents were measured at peak. a holding potential of - pulses from a holding

Peak currents before cinnarizine were normalized 80mV at 1 sec and 5 sec potential of -80mV at 1 sec

to 1 (n = 5). in the absence and and 5 sec in the absence

presence of 200 µM and presence of 200 µM

cinnarizine. (B) Eighty cinnarizine. (B) Eighty

Cinnarizine SUMMURY repeated 200 ms +50 mV repeated 200 ms +50 mV

depolarization pulses from depolarization pulses from

1. Cinnarizine is an antagonist of several a holding potential of -80 a holding potential of -80

Figure 1. Structure of cinnarizine. vasoactive drugs including adrenaline, mV at 1 sec and 5 sec in mV at 1 sec and 5 sec in
angiotensin and 5-hydroxytryptamine. the absence and presence the absence and presence

2. Inhibition of Kv1.5 channel by ifenprodil was of 200 µM cinnarizine. (C) of 200 µM cinnarizine. (C)

reversible after washing for 30 min, peak Peak current blockade by Steady-state current

current reversed by ~100%, steady-state 200 µM cinnarizine after blockade by 200 µM

reversed by ~98%. 15 pulses at 1 sec cinnarizine after 15 pulses

intervals. Increasing the at 1 sec intervals.

3. Cinnarizine block Kv1.5 depend on frequency, depolarization intervals to

1 sec interval is best blocked and the longer 15 sec in the presence of Increasing the

the interval, the lower the blocking rate. cinnarizine resulted in a depolarization intervals to
15 sec in the presence of

partial relief, and changing cinnarizine resulted in a

back to 1 sec intervals partial relief, and changing

increased Kv1.5 channel back to 1 sec intervals

blockade again. Peak increased Kv1.5 channel

currents of first pulse were blockade again. Steady-

normalized to 1. Symbols state currents of first pulse

with error bars represent were normalized to 1.

mean ± S.E.M. (n = 8). Symbols with error bars

represent mean ± S.E.M.

(n =8).