J Korean Med Sci.  2007 Feb;22(1):57-62. 10.3346/jkms.2007.22.1.57.

Sodium-activated Potassium Current in Guinea pig Gastric Myocytes

• Kim YC
• Sim JH
• Kang TM
• Suzuki H
• Kim SR
• Kwon SC
• Xu WX
• Lee SJ
• Kim KW

• KMID: 1713230
• DOI: http://doi.org/10.3346/jkms.2007.22.1.57

Abstract

This study was designed to identify and characterize Na+ -activated K+ current (I(K(Na))) in guinea pig gastric myocytes under whole-cell patch clamp. After whole-cell configuration was established under 110 mM intracellular Na+ concentration ([Na+]i) at holding potential of -60 mV, a large inward current was produced by external 60 mM K+([K+] degree). This inward current was not affected by removal of external Ca2+. K+ channel blockers had little effects on the current (p>0.05). Only TEA (5 mM) inhibited steady-state current to 68+/-2.7% of the control (p<0.05). In the presence of K+ channel blocker cocktail (mixture of Ba2+, glibenclamide, 4-AP, apamin, quinidine and TEA), a large inward current was activated. However, the amplitude of the steadystate current produced under [K+]degree (140 mM) was significantly smaller when Na+ in pipette solution was replaced with K+ - and Li+ in the presence of K+ channel blocker cocktail than under 110 mM [Na+]i. In the presence of K+ channel blocker cocktail under low Cl- pipette solution, this current was still activated and seemed K+ -selective, since reversal potentials (E(rev)) of various concentrations of [K+]degree-induced current in current/voltage (I/V) relationship were nearly identical to expected values. R-56865 (10-20 microgram), 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.

Keyword

Muscle, Smooth; Myocytes, Smooth Muscle; Gastrointestinal Tract; Stomach; Na+ -activated K+ Current (I(K(Na))); Guinea Pigs

MeSH Terms

Tetraethylammonium Compounds/pharmacology
Stomach/*physiology
Sodium/metabolism/*pharmacology
Potassium Channels/*physiology
Potassium Channel Blockers/pharmacology
Myocytes, Smooth Muscle/*physiology
Membrane Potentials
Male
Guinea Pigs
Female
Chlorides/pharmacology
Calcium/metabolism
Animals

Figure

• 

  Fig. 1 Na+-induced inward current in guinea pig gastric myocytes. Whole-cell current was recorded at a holding potential of -60 mV. Under K+-rich pipette solution, less than -50 pA of inward current is produced by the application of 140 mM [K+]o in Aa. Panel Ab shows 60 mM [K+]o-induced large inward current produced under 110 mM [Na+]i. In the right panel, representative I/V relationship of Na+-induced inward current activated by 60 mM [K+]o is shown. In B, Na+-induced inward currents are blocked by total replacement of [K+]o by 140 mM [NMDG+]o and [Cs+]o under 110 mM [Na+]i, respectively.

• 

  Fig. 2 Characteristics of Na+-induced inward current in guinea pig gastric myocytes. Ionic selectivity of the Na+-induced inward current was studied. I/V relationship of K+-induced inward current under 80 mM [Na+]i is shown in A, where ramp-hyperpolarizing pulse was applied. Reversal potentials (Erev) of each current recorded under 60 mM [K+]o was shifted to rightwards direction under and 140 mM [K+]o. Each reversal potential recorded was close to calculated one. Panel B shows inhibitory effects of 5 mM TEA on Na+-induced inward currents. In C, effects of K+ channel blockers on Na+-induced inward currents induced by 140 mM [K+]o under 110 mM [Na+]i, 110 mM [Li+]i and low [Cl-]i conditions are summarized (see the result for the detail). Averaged results are shown (mean±SEM) and numbers in parentheses indicate the number of cells examined.

• 

  Fig. 3 Characteristics of Na+-induced inward current in the presence of K+ channel blockers and low Cl--pipette solution in guinea pig gastric myocytes. (A) At a holding potential of -60 mV, K+-induced inward current was activated by application of 140 mM [K+]o in the presence K+ channel blocker cocktail (mixture of Ba2+ (100 µM), glibenclamide (10 µM), TEA (10 mM), 4-AP (10 mM), and apamin (300 nM)). Panel Ba shows I/V relationship of K+-induced inward current under low Cl- and 110 mM [Na+]i in the presence of K+ channel blocker cocktail. In Bb, Erev obtained in I/V relationship of Fig. 3Ba were plotted against [K+]o to identify the major charge carrier of this current. The dotted data was fit very well with the line which represents the theoretical Ek calculated from Nernst equation. The obtained data have a slope of 56 mV per 10-fold change of [K+]o.

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  Fig. 4 Effect of R-56865 on Na+-induced inward current in guinea pig gastric myocytes. (A) In the presence of K+ channel blockers cocktail under low Cl- pipette solution, K+-induced inward current is activated by application of 140 mM [K+]o at a holding potential of -60 mV. This current is blocked by application of 10 µM R-56865 in a reversible manner. In Panel B, inhibitory effects of R-56865 (10 and 20 µM) on Na+-induced inward current are summarized. The numbers above the columns indicate the number of cells examined.

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