Phasic contractions

Palytoxin (PTX), isolated from the zanthid Palythoa species, caused a rapid contraction followed by a slow phasic contraction of the guinea pig vas deferens. The second component of PTX-induced contraction was markedly inhibited by adrenergic blocking agents, whereas the first component was blocked by ouabain. In pheochromocytoma cells,... 

Manometry remains the gold standard test, because phasic contractions are generally lumen occlusive in small bowel and thus reliably detected by intraluminal pressure measurements. Transit tests are more convenient nevertheless, they are time-consuming and do not provide the same detailed information about contractile activity [114, 115], These methods are briefly discussed. 

Nelson We have done experiments on urinary bladder from guinea pig and mouse, and ryanodine does not decrease the phasic contractions, it increases them. It looks like the net effect of activating the RyRs to brake contractility. Presumably it does this by decreasing excitability. 

Nelson I think it affects the bursting. There is another clock here. If we add iberiotoxin to bladder strips, the amplitudes and durations of the phasic contractions increase. We also observe a slowing of the phasic contraction frequency. This suggests that it is some sort of slow Ca2+ dependent process that causes longer periods between contractions. The net effect of iberiotoxin is a large increase in force amplitude and duration rise, the frequency goes down. 

Nelson A phasic contraction presumably results from a train of action potentials. 

Burdyga Yes. In the guinea-pig ureter application of caffeine (1—2 mM) increases the frequency of Ca2+ sparks and STOCs, and under current-clamp conditions this causes a decrease of the plateau component of the action potential, thus bringing down the Ca2+ and force. In contrast, CPA inhibits Ca2+ sparks and STOCs, and increases the duration of the plateau component of the action potential. This results in an increase in the duration of the Ca2+ transient and amplitude and duration of the phasic contraction. 

Arum palaestinum contains isoorientin and vitexin, which were studied for their antispasmodic activity on isolated organs. Isoorientin in concentrations ranging from 10 to 6 X 10 M decreased the frequency and the amplitude of the phasic contractions of uterine... 

The effect of. S divinorum on duodenal smooth muscle is not clear, although the extract appears to decrease the frequency of phasic contractions while increasing their duration. Typically, contractions occurred approximately once every two seconds when the muscle was bathed in pure Tyrode s solution. However, when bathed in 100% S. divinorum extract, contractions appeared to stop completely. When flushed with Tyrode s solution, the muscle recovered almost completely. Wlien the duodenum was bathed in 50%. S divinorum extract, the muscle would contract for approximately 15 seconds, relax for about 2 seconds, and then contract again. By comparison, when the muscle was bathed in extract of L. nobilis, the muscle would stop contracting and would not recover when flushed with Tyrode s solution. Figure 3 shows the tracings produced from a single strip of duodenal smooth muscle treated with. S divinorum. 

Besides sperm dysfunction, comparison of PMCA4 null 129/SvJ and Black Swiss mixed background mice revealed a strain specific smooth muscle phenotype, impaired phasic contractions and an apoptotic tendency for portal vein smooth... 

Garfield RE. 1995. Mechanism underlying phasic contractions of pregnant rat myometrium simulated by aluminum fluoride. Am J Obstet Gynecol 173 348-349. 

After a 15-min equilibration period at zero volume, variations in intraluminal pressure are recorded in response to continuous infusion of saline at a rate of 2.8 ml/h at 37 °C for 30-40 min by means of a peristaltic pump connected to the polyethylene tubing inserted into the bladder. This infusion rate simulates the maximal hourly diuresis within the physiological range. In each preparation the infusion is continued until micturition occurs. Micturition is referred as the emission of several drops of fluid during a sustained phasic contraction of the detrusor muscle which is followed by return to zero or, in any case, to a value lower than that recorded just before micturition. 

The leucokinins (LK s) are a new class of insect myotropic neuropeptides isolated from head extracts of the cockroach L. maderae. These octapeptides all contain a similar core sequence of 5 amino acids that extend from position 4 through 8. This sequence Phe-X-Ser-Trp-Gly-NH2 seems to be required for hindgut stimulation. The initial response of the hindgut to the LK s was characterized by an increase in the frequency and/or amplitude of phasic contractions (50, ). At higher peptide concentrations, a tonic component was generally present. All of the LK s showed a response at 3 x 10 M that was 5-10% above the mean level of spontaneous activity. The maximum response for each of the peptides was recorded at a concentration 2.1 X 10" M. Thus, the intrinsic activities for the LK s are nearly equal because the dose-response curves have about the same asymptotic limits. A comparison of the dose concentrations that gave a half maximal response (ED q) for the 8 peptides is shown in Table I. 

Hurwitz et al. (32) extended these ideas by giving evidence, again in a nonsecretory tissue, for two potential dependent calcium channels. These authors showed that the calcium channel associated with the phasic contraction of guinea pig ileal smooth muscle was blocked by lanthanum, but the calcium channel mediating the tonic contraction was not. In this system, both these channels were potential dependent. Hence, a variety of calcium channels may exist on cell surfaces. 

Because earlier studies in this and other laboratories showed that inhibitors of tyrosine kinase activity suppressed contraction of smooth muscle (Section II), we suspected that vanadate-induced contraction might be due to its efficacy as an inhibitor of tyrosine phosphatase activity. Our experiments showed that treatment of taenia coli with 1.5 mM vanadate induced a tonic contraction that was associated with enhanced tyrosine phosphorylation of at least three substrates (M 85,000, 116,000, and 205,000 Figs. 2A and 2B). Maximal force attained in response to vanadate was about one-fourth to one-third of the maximal force attained during the phasic contraction elicited by stimu-... 

The rabbit intestinal segments showed rhythmic contractions superimposed on the basal tonus. Porcine motilin caused an increase in the basal tonus in a concentration-dependent manner without affecting the frequency of phasic contractions. The sensitivity of the response to motilin decreased aboradly the minimum effective concentrations for the duodenum, jejunum, and ileum were 1 x 10 , 3 X 10, and 1 x 10 M, respectively. The maximal contractile responses of the duodenum, jejunum, and ileum were 89%, 50%, and 11%, respectively. 

The more stable analog of anandamide, methanandamide, does not affect indomethacin-induced phasic contractions of guinea-pig deum that are generated at the muscle level as they are left unchanged by tetrodotoxin (Heinemann et al., 1999). 

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