Page 39 - F. Cell biology

Effect of Ifenprodil on Kv1.5 Channel Currents

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 +50

Ifenprodil(2-(4-benzyl-piperidino)-1-(4-hydroxyphenyl)- 1.1 20 µM Ifenprodil -40

1-pro-panol) bind to but do not activate alpha- -80 -60 -80mV

adrenergic receptors thereby blocking the actions of 1.0

endogenous or exogenous adrenergic agonists. 0.9

Adrenergic alpha-antagonists are used in the treatment

of hypertension, vasospasm, peripheral vascular 0.8

disease, shock, and pheochromocytoma. Kv1.5 Normalized peak current 100 νA

channels are expressed in the heart and pancreatic 0.7 100 ms

beta-cells. The most studied is the human Kv1.5 Wash out Control Control 30 μM Ifenprodil

control
channel (hKv1.5), which is thought to underlie the ultra- 0.6 20 µM Ifenprodil
20uM ifenprodil

rapidly activating delayed rectifier K current I kur found B
+

in human atrial myocytes. We examined the effect of 0.5 0 10 20 30 40 50 60

ifenprodil on the human Kv1.5 channel using a 1.0 control
1.0
Control

Xenopus oocyte expression system and a two- B Time (min) 0.8 30uM
30 µM Ifenprodil
0.8

microelectrode voltage clamp technique. We examined

0.6
the reversibility of ifenprodil inhibition of Kv1.5 currents. 0.6

Inhibition was reversible even after washing for 30 min, 1.1 20 µM Ifenprodil 0.4
0.4

peak currents reversed by 86%, steady-state reversed Normalized tail 0.2
0.2
by 77%. And ifenprodil did not shift activation and 1 current

0.0
inactivation curve. These results suggested that 0.0

ifenprodil inhibit Kv1.5 currents via a non-genomic 0.9 -60 -40 -20 0 0 20 40 60
20
40
60
-20
-60
-40
mechanism, cannot cross plasma membrane, the effect Membrane potential (mV)

Normalized steady-state current 0.8
may be short lasting.

0.7 Figure 3. Effects of ifenprodil on steady state

control activation of Kv1.5 channels. (A) Representative
Control
0.6 20uM ifenprodil

Wash out 20 µM Ifenprodil steady state activation tail currents recorded at −40

0.5 mV after 100-ms depolarizing pulses from −60 to+ 50

0 10 20 30 40 50 60 mV in the absence and presence of 30 μM ifenprodil.

KEY WORDS Time (min) (B) Steady state activation curves were obtained by

Figure 2. Reversible inhibitions of Kv1.5 normalizing each tail current to the tail current of +50

Ifenprodil; Kv1.5 channel; Non-genomic; channels by ifenprodil. (A,B) Peak current and mV by fitting data with a Boltzmann equation.

Potassium channel steady-state current recordings before and after Symbols with error bars represent mean± SEM (n =

washing out 20 μM ifenprodil. Currents were 10)

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

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

Normalized peak currents were measured at peak.

Peak currents before ifenprodil were normalized to

1 (n = 5). -80 -60 -80mV

SUMMURY

1. Ifenprodil is α -adrenergic receptor antagonist, 1.5 µA
1
interacts with serotonin, and sigma receptors.

Ifenprodil is initially developed as a vasodilating Control 30 μM Ifenprodil 10 ms

Ifenprodil and anti-ischemic agent. B

2. Inhibition of Kv1.5 channel by ifenprodil was

1.0
Figure 1. Structure of Ifenprodil. reversible after washing for 30 min, peak current 1.0

reversed by ~83%, steady-state reversed by 0.8

0.8
~71%.

0.6
Normalized peak current 0.6
3. Ifenprodil did not affect the slope degree of either

Control
activation or inactivation curves. 0.4 control
0.4
30uM
30 µM Ifenprodil

0.2
0.2
-60 -40 -20 0 0 20
-40
-20
20
-60
Membrane p
otential (mV)

Figure 4. Effects of ifenprodil on steady state

inactivation of Kv1.5 channels. (A) Representative

tail currents were elicited by 250 ms depolarizing

pulses to +50 mV; 30-s preconditioning pulses were

−60 to +20 mV in the absence and presence of 30

μM ifenrprodil. (B) Steady state inactivation curves

were obtained by normalizing each tail current to the

tail current when depolarized to +50 mV by fitting

data with a Boltzmann equation. Symbols with error

bars represent mean± SEM (n = 7)