Metabolic dependency of ionophore A23187‐induced contraction of ileal longitudinal smooth muscle

Abstract

1. Tonic contraction in response to K+ is well known to be highly dependent on aerobic metabolism in ileal muscle. The ionophore A23187 (10(-5) M) induced an initial contraction and successive rhythmic contraction in ileal muscle, but did not induce tonic contraction. This study, therefore, was performed to investigate the metabolic dependency during contraction induced by A23187. 2. Under hypoxic conditions, A23187 (10(-5) M) induced an initial contraction accompanied by an increase in lactate release. However, it induced only small rhythmic contractions and decreases in ATP, phosphocreatinine (PCr) and glycogen contents. 3. In glucose-free medium, A23187 (10(-5) M) induced an initial contraction and concomitant significant decrease in the ATP and glycogen contents. However, it did not induce successive rhythmic contractions. In 'glycogen-depleted muscle' stimulated repeatedly with 60 mM K+ in glucose-free medium, 60 mM K+ induced a phasic contraction without tonic contraction. A23187 induced no contraction under these conditions. 4. These results suggested that the initial contraction induced by A23187 was dependent on endogenous glycogen, while successive rhythmic contractions were dependent on aerobic metabolism after supply of external glucose to the ileal muscle.

The spasmolytic effect of Aloysia citriodora, Palau (South American cedrón) is partially due to its vitexin but not isovitexin on rat duodenums

“…This mechanism of papaverine was also the most important in other spontaneously depolarized smooth muscles as guinea-pig urinary bladder (Shimizu et al, 2000a) and rat uterus (Shimizu et al, 2000b). Thus, we assayed AEC on rat duodenums upon a hypoxic-free glucose medium (Nasu and Nishikawa, 2000), founding that the tonic contraction was more sensitive than the phasic, as it was reported (Nakagawa et al, 1976). In ileal muscle the phasic contraction depends on the endogenous glycogen while the tonic depends on aerobic metabolism (Nasu and Nishikawa, 2000).…”

“…Thus, we assayed AEC on rat duodenums upon a hypoxic-free glucose medium (Nasu and Nishikawa, 2000), founding that the tonic contraction was more sensitive than the phasic, as it was reported (Nakagawa et al, 1976). In ileal muscle the phasic contraction depends on the endogenous glycogen while the tonic depends on aerobic metabolism (Nasu and Nishikawa, 2000). Fig.…”

Signal Transduction Underlying the Inhibitory Mechanism of Fluoxetine on Electrical Field Stimulation Response in Rat Ileal Smooth Muscle

“…To evaluate the mechanism of FLX, muscle strips were incubated with each antagonist for 20 min and contraction was induced by EFS. They were then administrated with FLX and the inhibitory effect of FLX on EFS-induced muscle contraction was compared in the absence and presence of antagonists; L-NAME (10 µmol/l) [48], atropine (1 µmol/l) [49], guanethidine (10 µmol/l) [50], bicuculline (10 µmol/l), phacolfen (10 µmol/l), methysergide (100 µmol/l), ketanserin (1 µmol/l), ondansetron (1 µmol/l), GR 113808 (10 µmol/l) [49], nifedipine (1 µmol/l), calcium ionophore A23187 (1 µmol/l) [51], U73122 (1 µmol/l), chelerythrine (10 µmol/l), ML-9 (10 µmol/l), Y27632 (1 µmol/l) [52], TEA (10 mmol/l), 4-AP (100 µmol/l) and glybenclamide (10 µmol/l) [33]. Muscle strips were equilibrated for 30 min after washing with Kreb's solution for 3 times between each part within each sets of experiment.…”