Signal transduction of bombesin-induced circular smooth muscle cell contraction in cat esophagus

AIM： To investigate the mechanism of bombesin-induced circular smooth muscle cell contraction in cat esophagus. METHODS： Specific G protein or phospholipase C involved in cat esophagus contraction was identified, muscle cells were permeabilized with saponin. After per- meabilization of muscle cells, the Gi3 antibody inhibited bombesin-induced smooth muscle cell contraction. RESULTS： Incubation of permeabilized circular muscle cells with PLC-β3 antibody could inhibit bombesin-induced contraction. H-7, chelerythrine （PKC inhibitor） and genistein （protein tyrosine kinase inhibitor） inhibited bombesin-induced contraction, but DAG kinase inhibitor, R59949, could not inhibit it. To examine which mitogen-activated protein kinase （MAPK） was involved in bombesin-induced contTaction, the specific MAPK inhibitors （MEK inhibitor, PD98059 and p38 MAPK inhibitor, SB202190） were used. Preincubation of PD98059 blocked the contraction induced by bombesin in a concentration-dependent manner. However, SB202190 had no effects on contraction. CONCLUSION： Bombesin-induced circular muscle cell contraction in cat esophagus is mediated via a PKC or a PTK-dependent pathway or p44/p42 HAPK pathway.

Observations on the Contraction and Movement of Fat-Storing Cells in Culture

The Wister fat-storing cells were isolated by perfusion with collagenase and centrifugation with metrizamide density cushion technique and cultured in vitro. The fatstoring cells were confirmed by the presentation of the lipid drop in the cytoplasm and the visualization of dismin with anti-dismin antibody by using indirect immunofluorescence method. By the videotape recorder (VIR) and the imagine analysis system, we observed the wandering immigration, the abrupt contraction of fat-storing cells with spike, then becoming a ball-like shape in its division phase. After that the cell began to extend and the contraction of these cells can be induced by the presence of 10-2 mmol/L endothelin-1 , 1 mmol/L of substance P and 2×10-5 mmol/L noradrenalin. After removal of these agents the contracted cells would become extended. All these findings indicate that the fat-storing cells have ability of contraction and movement.

Effect of the ginsenoside Rb1 on the spontaneous contraction of intestinal smooth muscle in mice

AIM: To investigate the effect and the possible mechanism of ginsenoside Rb1 on small intestinal smooth muscle motility in mice. METHODS: Intestinal smooth muscle strips were isolated from male ICR mice (5 wk old), and the effect of ginsenoside Rb1 on spontaneous contraction was recorded with an electrophysiolograph. The effect of ginsenoside Rb1 on ion channel currents, including the voltage-gated K + channel current (IK V ), calcium-activated potassium channel currents (IK Ca ), spontaneous transient outward currents and ATP-sensitive potassium channel current (IK ATP ), was recorded on freshly isolated single cells using the whole-cell patch clamp technique. RESULTS: Ginsenoside Rb1 dose-dependently inhibited the spontaneous contraction of intestinal smooth muscle by 21.15% ± 3.31%, 42.03% ± 8.23% and 67.23% ± 5.63% at concentrations of 25 μmol/L, 50 μmol/L and 100 μmol/L, respectively (n=5,P<0.05). The inhibitory effect of ginsenoside Rb1 on spontaneous contraction was significantly but incompletely blocked by 10 mmol/L tetraethylammonium or 0.5 mmol/L 4-aminopyridine, respectively (n=5, P<0.05). However, the inhibitory effect of ginsenoside Rb1 on spontaneous contraction was not affected by 10 μmol/L glibenclamide or 0.4 μmol/L tetrodotoxin. At the cell level, ginsenoside Rb1 increased outward potassium currents, and IK V was enhanced from 1137.71 ± 171.62 pA to 1449.73 ± 162.39 pA by 50 μmol/L Rb1 at +60 mV (n=6, P<0.05). Ginsenoside Rb1 increased IK Ca and enhanced the amplitudes of spontaneous transient outward currents from 582.77 ± 179.09 mV to 788.12 ± 278.34 mV (n=5, P<0.05). However, ginsenoside Rb1 (50 μmol/L) had no significant effect on IK ATP (n=3, P<0.05). CONCLUSION: These results suggest that ginsenoside Rb1 has an inhibitory effect on the spontaneous contraction of mouse intestinal smooth muscle mediated by the activation of IK V and IK Ca , but the K ATP channel was not involved in this effect.