Korean J Physiol Pharmacol.  2011 Dec;15(6):405-413. 10.4196/kjpp.2011.15.6.405.

Nitric Oxide-mediated Relaxation by High K+ in Human Gastric Longitudinal Smooth Muscle

• Kim YC
• Choi W
• Yun HY
• Sung R
• Yoo RY
• Park SM
• Yun SJ
• Kim MJ
• Song YJ
• Xu WX
• Lee SJ

• KMID: 2285428
• DOI: http://doi.org/10.4196/kjpp.2011.15.6.405

Abstract

This study was designed to elucidate high-K+induced response of circular and longitudinal smooth muscle from human gastric corpus using isometric contraction. Contraction from circular and longitudinal muscle stripes of gastric corpus greater curvature and lesser curvature were compared. Circular smooth muscle from corpus greater curvature showed high K+ (50 mM)-induced tonic contraction. On the contrary, however, longitudinal smooth muscle strips showed high K+ (50 mM)-induced sustained relaxation. To find out the reason for the discrepancy we tested several relaxation mechanisms. Protein kinase blockers like KT5720, PKA inhibitor, and KT5823, PKG inhibitor, did not affect high K+-induced relaxation. K+ channel blockers like tetraethylammonium (TEA), apamin (APA), glibenclamide (Glib) and barium (Ba2+) also had no effect. However, N(G)-nitro-L-arginine (L-NNA) and 1H-(1,2,4) oxadiazolo (4,3-A) quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase (sGC) and 4-AP (4-aminopyridine), voltage-dependent K+ channel (KV) blocker, inhibited high K+-induced relaxation, hence reversing to tonic contraction. High K+-induced relaxation was observed in gastric corpus of human stomach, but only in the longitudinal muscles from greater curvature not lesser curvature. L-NNA, ODQ and KV channel blocker sensitive high K+-induced relaxation in longitudinal muscle of higher portion of corpus was also observed. These results suggest that longitudinal smooth muscle from greater curvature of gastric corpus produced high K+-induced relaxation which was activated by NO/sGC pathway and by KV channel dependent mechanism.

Keyword

Human stomach; Relaxation; Nitric oxide (NO); Longitudinal smooth muscle; High K+

MeSH Terms

Apamin
Barium
Carbazoles
Contracts
Glyburide
Guanylate Cyclase
Humans
Intracellular Signaling Peptides and Proteins
Isometric Contraction
Muscle, Smooth
Muscles
Protein Kinases
Pyrroles
Relaxation
Stomach
Tetraethylammonium
Apamin
Barium
Carbazoles
Glyburide
Guanylate Cyclase
Intracellular Signaling Peptides and Proteins
Protein Kinases
Pyrroles
Tetraethylammonium

Figure

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  Fig. 1 Isometric contraction of circular and longitudinal smooth muscle of corpus greater curvature (GC). Circular muscle of human gastric corpus GC showed spontaneous contraction (A). In panel (B), high-K+ produced initial and tonic contraction. Data was summarized in (C). Longitudinal muscles of corpus GC also showed spontaneous contraction (D). However, high K+ produced sustained relaxation (E). Each data from circular and longitudinal muscle were summarized in (C, F).

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  Fig. 2 Effect of protein kinase inhibitors on high K+-induced relaxation of longitudinal smooth muscle of corpus GC. Sodium nitroprusside (SNP)-induced relaxation of longitudinal muscle was studied. SNP (3~5 µM) produced relaxation (A) and data was summarized in (B). High K+-induced relaxation was also studied in the presence of KT 5720, which is known to inhibit PKA. As shown in (C) and (D), high K+-induced sustained relaxation was not affected by pretreatment of KT 5720. High K+-induced relaxation was also studied by pretreatment of KT 5823, inhibitor of PKG. In the presence of KT 5823 (1 µM), high K+ produced sustained relaxation too (E).

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  Fig. 3 Effect of L-NNA, ODQ and 4-aminopyridine (4-AP) on high K+-induced relaxation of longitudinal smooth muscle of corpus GC. High K+-induced relaxation was also studied in the presence of L-NNA. As shown in (A) and (B), high K+-induced relaxation was blocked relaxation and transited it to contraction by pretreatment of L-NNA and ODQ. Data was summarized in (B). Effect of 4-aminopyridine (4-AP), KV channel blocker, on high K+-induced relaxation. In the presence or absence of NBC, pretreatment of 4-AP blocked relaxation and transited it to contraction (C, D).

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  Fig. 4 Isometric contraction of circular smooth muscle of corpus lesser curvature (LC) of human stomach. Contractile properties of circular and longitudinal smooth muscles of corpus LC was studied. Circular muscle of human gastric corpus LC showed spontaneous contraction (A). In panel (B), high-K+ produced initial and tonic contraction. Data was summarized in (C). Meanwhile, longitudinal muscles of corpus LC also showed spontaneous contraction (D). However, high K+ produced initial contraction followed by weak contraction in longitudinal muscle of corpus LC (E). Data was summarized in (F). We also studied effect of L-NNA on high K+-induced contraction in longitudinal muscle of corpus LC (G). L-NNA (100 µM) produced tonic (0.5 g) and phasic contractions (0.4 g) and high K+ in the presence of L-NNA produced initial (4.5 g) and sustained contraction (6.3 g), respectively. Data was summarized in (H). In (I) and (J), ACh-induced contraction is shown. ACh (10 µM) produced initial transient contraction followed by later sustained tonic contraction with superimposed phasic contractions.

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  Fig. 5 Isometric contraction of circular and longitudinal muscle of higher portion of corpus GC. Circular muscle of human gastric higher portion of corpus GC showed spontaneous contraction (A). In panel (B), high-K+ produced initial and tonic contraction. Longitudinal muscles also showed spontaneous contraction (C). However, high K+ produced sustained relaxation (D). This relaxation in longitudinal muscle was not affected by pretreatment of TEA 5 mM (E) and K+ channel blockers cocktail (F). However, high K+-induced relaxation was blocked and transited to contraction by pretreatment of L-NNA (G, H).

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