Muscarinic activity modulated by C-type natriuretic peptide in gastric smooth muscles of guinea-pig stomach

Excitatory regulation of angiotensin II on gastric motility and its mechanism in guinea pig

In the present study, we investigated the effect of Ang II on gastric smooth muscle motility and its mechanism using intracellular recording and whole-cell patch clamp techniques. Ang II dose-dependently increased the tonic contraction and the frequency of spontaneous contraction in the gastric antral circular smooth muscles of guinea pig. ZD7155, an Ang II type 1 receptor (AT(1)R) blocker, completely blocked the effect of Ang II on the spontaneous contraction of gastric smooth muscle. In contrast, TTX, a sodium channel blocker, failed to block the effect. Furthermore, nicardipine, a voltage-gated Ca(2+)-channel antagonist, did not block the effect of Ang II on the tonic contraction of gastric smooth muscle, but external free-calcium almost completely blocked this effect. Both ryanodine, an inhibitor of calcium-induced Ca(2+) release (CICR) from ryanodine-sensitive calcium stores, and thapsigargin, which depletes calcium in calcium stores, almost completely blocked the effect of Ang II on tonic contraction. However, 2-APB, an inositol trisphosphate (IP(3)) receptor blocker, significantly, but not completely, blocked the Ang II effect on tonic contraction. We also determined that Ang II depolarized membrane potential and increased slow wave frequency in a dose-dependent manner. It also inhibited delayed rectifying potassium currents in a dose-dependent manner, but did not affect L-type calcium currents or calcium-activated potassium currents. These results suggest that Ang II plays an excitatory regulation in gastric motility via AT(1)R-IP(3) and the CICR signaling pathway. The Ang II-induced inhibition of delayed rectifying potassium currents that depolarize membrane potential is also involved in the potentiation of tonic contraction and the frequency of spontaneous contraction in the gastric smooth muscle of guinea pig.

Effect of dendroaspis natriuretic peptide (DNP) on L-type calcium channel current and its pathway

Dendroaspis natriuretic peptide (DNP), a newly-described natriuretic peptide, relaxes gastrointestinal smooth muscle. L-type calcium channel currents play an important role in regulating smooth muscle contraction. The effect of DNP on L-type calcium channel currents in gastrointestinal tract is still unclear. This study was designed to investigate the effect of DNP on barium current (I(Ba)) through the L-type calcium channel in gastric antral myocytes of guinea pigs and cGMP-pathway mechanism. The whole-cell patch-clamp technique was used to record L-type calcium channel currents. The content of cGMP in guinea pig gastric antral smooth muscle and perfusion solution was measured using radioimmunoassay. DNP markedly enhanced cGMP levels in gastric antral smooth muscle tissue and in perfusion medium. DNP concentration-dependently inhibited I(Ba) in freshly isolated guinea pig gastric antral circular smooth muscle cells (SMCs) of guinea pigs. DNP-induced inhibition of I(Ba) was partially blocked by LY83583, an inhibitor of guanylate cyclase. KT5823, a cGMP-dependent protein kinase (PKG) inhibitor, almost completely blocked DNP-induced inhibition of I(Ba). However, DNP-induced inhibition of I(Ba) was potentiated by zaprinast, an inhibitor of cGMP-sensitive phosphodiesterase. Taken together, DNP inhibits L-type calcium channel currents via pGC-cGMP-PKG-dependent signal pathway in gastric antral myocytes of guinea pigs.

Dual effect of exogenous hydrogen sulfide on the spontaneous contraction of gastric smooth muscle in guinea-pig

Hydrogen sulfide (H(2)S) is produced endogenously in mammalian tissues and is important in both physiological and pathological processes. Despite its importance, little is known regarding the effect of H(2)S on gastrointestinal motility. We evaluated the effect of H(2)S on the spontaneous contraction of gastric antrum smooth muscle in the guinea pig (Cavia porcellus) using a physiograph. In addition, we investigated whether the effect of H(2)S was mediated by ionic channels by recording membrane currents in freshly dispersed gastric antrum myocytes using a whole-cell patch clamp. Sodium hydrogen sulfide (NaHS), an H(2)S donor, had a dual effect on the spontaneous contraction of gastric antrum muscle strips. At high concentrations (0.3-1.0 mM), NaHS suppressed the amplitude of spontaneous contraction. At low concentrations (0.1-0.3 mM), NaHS enhanced the resting tension of muscle strips while slightly reducing the contractile amplitude. The excitatory effect on spontaneous contraction, caused by low concentrations of NaHS, was abolished when the muscle strips were pretreated with 10 mM tetraethylammonium (TEA), a nonselective potassium channel blocker, or 0.5 mM 4-Aminopyridine (4-AP), a voltage-gated K(+) channel blocker. However, the excitatory effect of NaHS was not completely blocked by low concentrations of TEA (1 mM). Pretreatment with both TEA (1 mM) and 4-AP (0.5 mM) completely abolished the excitatory effect. The dose-response curve for the inhibitory effect of NaHS on the spontaneous contraction of gastric smooth muscle was shifted significantly to the left by TEA and 4-AP. Both Pinacidil, a K(ATP) channel opener, and NaHS significantly inhibited TEA-potentiated spontaneous contraction. Glibenclamide, a K(ATP) channel blocker, partially, but significantly, reversed the reduction in amplitude. NaHS enhanced the amplitude of the K(ATP) current, but inhibited the voltage-gated K(+) channel current (IK(V)) in a dose-dependent manner. NaHS had no effect on STOC at low concentrations (0.1-1.0 mM) but significantly inhibited STOC at high concentrations (4-10 mM). Our results suggest that H(2)S has multiple actions during the regulation of gastric motility in the guinea-pig. An excitatory effect is mediated via inhibition of the voltage-gated K(+) channel and an inhibitory effect is mediated via activation of the K(ATP) channel.

Duodeno-jejunal junction dyssynergia: Description of a novel syndrome

AIM: To investigate the hypothesis that duodeno-jejunal dyssynergia existed at the duodeno-jejunal junction.

METHODS: Of 112 patients who complained of epigastric distension and discomfort after meals, we encountered nine patients in whom the duodeno-jejunal junction did not open on duodenal contraction. Seven healthy volunteers were included in the study. A condom which was inserted into the 1^st duodenum was filled up to 10 mL with saline in increments of 2 mL and pressure response to duodenal distension was recorded from the duodenum, duodeno-jejunal junction and the jejunum.

RESULTS: In healthy volunteers, duodenal distension with 2 and 4 mL did not produce pressure changes, while 6 and up to 10 mL distension effected significant duodenal pressure increase, duodeno-jejunal junction pressure decrease but no jejunal pressure change. In patients, resting pressure and duodeno-jejunal junction and jejunal pressure response to 2 and 4 mL duodenal distension were similar to those of healthy volunteers. Six and up to 10 mL 1^st duodenal distension produced significant duodenal and duodeno-jejunal junction pressure increase and no jejunal pressure change.

CONCLUSION: Duodeno-jejunal junction failed to open on duodenal contraction, a condition we call ‘duodeno-jejunal junction dyssynergia syndrome’ which probably leads to stagnation of chyme in the duodenum and explains patients' manifestations.