K+channels play an important role in regulating the mem-
brane potential of smooth muscles and their excitability. Gen-
erally, outward K+current oppose membrane excitability via
K+channels. In a variety of cells including gastrointestinal
(GI) tract, several types of K+channels which are activated
by diverse intracellular factors, such as Ca2+and ATP have
been reported (1-7). The best known among them is Ca2+-acti-
vated K+channel (K(Ca) channel) whose gating is regulated
by concentration of intracellular free Ca2+([Ca2+]i) (3-6). K(Ca)
channel participates principally in the rapid repolarization
of Ca2+-dependent action potentials (8). Voltage-dependent
and Ca2+-independent K+channels (K(V) channel) and ATP-
sensitive K+channel (KATP channel) in smooth muscles are
also known well (1, 7, 9). In GI tract, basal activation of KATP
channel has been shown to contribute to control of resting
membrane potential (RMP) (9). Recently, pH-sensitive two-
pore K+channels of the TASK family have also been report-
ed in murine GI tract (10). Therefore, it seems that more types
of K+channels still exist in GI smooth muscles. In fact, there
is another class of K+channel not reported in GI smooth mus-
cle cells. This is known as K(Na) channel, which is activated
by intracellular Na+([Na+]i). It was reported in guinea pig
ventricular myocytes (11).
Since its isolation from cardiac myocytes, the gating of K(Na)
channel has been known to be activated by intracellular Na+,
but not by Ca2+and ATP or other nucleotides (12). Depend-
ing on cell types and recording conditions, reported unitary
conductance of K(Na) channel ranges from 105 to 200 pS and
half-maximal activation by Na+occurs between 7 and 80 mM
(13). K(Na) channel of the heart was suggested to be activated
under pathophysiological conditions such as during failure
of the Na+-K+pump (11). Also K(Na) channel has been pro-
posed to be activated by a single action potential and could
be involved in setting RMP in neuronal cell (14-16). To date,
however, the existence of K(Na) channel in smooth muscles has
not been reported yet. In GI tract, spontaneous contraction
and slow wave are dependent on extracellular Na+concentra-
tion: In the duodenum and ileum, low Na+decreased ampli-
Young Chul Kim, Jae Hoon Sim*,
Tong Mook Kang
Seung Ryul Kim
Wen-Xie Xu¶, Sang Jin Lee,
Ki Whan Kim*
�, Hikaru Suzuki
�, Seong-Chun Kwon‖,
Departments of Physiology, Biochemistry
National University, College of Medicine, Cheongju;
Department of Physiology & Biophysics*, Seoul
National University, College of Medicine, Seoul;
Department of Physiology
School of Medicine, Suwon, Korea; Department of
Nagoya, Japan; Department of Physiology‖, College
of Medicine, Kwandong University, Gangneung, Korea;
Department of Physiology¶, Medical School, Shanghai
Jiaotong University, Shanghai, China
�, Sungkyunkwan University,
�, Nagoya City University Medical School,
Address for correspondence
Young Chul Kim
Department of Physiology, Chungbuk National
University College of Medicine, 12 Gaeshin-dong,
Heungduk-gu, Cheongju 361-763, Korea
Tel : +82.43-261-2859, Fax : +82.43-261-2859
E-mail : email@example.com
*This work was supported by Korea Research Foun-
dation Grant (KRF-2003-015-E00020).
J Korean Med Sci 2007; 22: 57-62
Copyright � The Korean Academy
of Medical Sciences
Sodium-activated Potassium Current in Guinea pig Gastric Myocytes
Received : 2 June 2006
Accepted : 19 July 2006
This study was designed to identify and characterize Na
in guinea pig gastric myocytes under whole-cell patch clamp. After whole-cell con-
figuration was established under 110 mM intracellular Na
holding potential of -60 mV, a large inward current was produced by external 60
channel blockers had little effects on the current (p>0.05). Only TEA (5 mM) inhib-
ited steady-state current to 68±±2.7% of the control (p<0.05). In the presence of K
channel blocker cocktail (mixture of Ba
TEA), a large inward current was activated. However, the amplitude of the steady-
state current produced under [K
pipette solution was replaced with K
er cocktail than under 110 mM [Na
under low Cl-pipette solution, this current was still activated and seemed K
tive, since reversal potentials (Erev) of various concentrations of [K
in current/voltage (I/V) relationship were nearly identical to expected values. R-56865
(10-20 M), a blocker of IK(Na), completely and reversibly inhibited this current. The
characteristics of the current coincide with those of IK(Na) of other cells. Our results
indicate the presence of IK(Na) in guinea pig gastric myocytes.
+]o). This inward current was not affected by removal of external Ca
2+, glibenclamide, 4-AP, apamin, quinidine and
+]o (140 mM) was significantly smaller when Na
+- and Li
+]i. In the presence of K
+in the presence of K
+channel blocker cocktail
Key Words : Muscle, Smooth; Myocytes, Smooth Muscle; Gastrointestinal Tract; Stomach; Na
Current (IK(Na)); Guinea Pigs
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