A mesoscopic description of contractile cytoskeletal meshworks

Epithelial morphogenesis plays a major role in embryonic development. During this process cells within epithelial sheets undergo complex spatial reorganization to form organs with specific shapes and functions. The dynamics of epithelial cell reorganization is driven by forces generated through the cytoskeleton, an active network of polar filaments and motor proteins. Over the relevant time scales, individual cytoskeletal filaments typically undergo turnover, where existing filaments depolymerize into monomers and new filaments are nucleated. Here we extend a previously developed physical description of the force generation by the cytoskeleton to account for the effects of filament turnover. We find that filament turnover can significantly stabilize contractile structures against rupture and discuss several possible routes to instability resulting in the rupture of the cytoskeletal meshwork. Additionally, we show that our minimal description can account for a range of phenomena that were recently observed in fruit fly epithelial morphogenesis.

[Pentachlorophenol--results of a Bavarian human monitoring program]

In connection with an investigation of state-owned buildings for wood preservatives, human monitoring on pentachlorophenol (PCP) was performed on 484 subjects from Northern Bavaria and 299 persons from Southern Bavaria during the period November 1994 to October 1995. Altogether, a similar pattern of concentrations resulted, the 95th percentile amounting to 15 (Northern Bavaria) and 20 micrograms PCP/l blood plasma (Southern Bavaria), respectively. An inquiry of the exposure conditions of the subjects studied in Southern Bavaria revealed that 28% had been exposed to wood containing 5-100 mg PCP/kg (slightly elevated) and 61 % to wood with > 100 mg PCP/kg (definitely treated). One-third each of the subjects had been exposed to dust containing 5 mg PCP/kg (normal), 5-10 mg/kg (slightly elevated) and > 10 mg/kg (clearly elevated), respectively. The mean exposure period was approx. 10 years with a mean daily stay of 8 hrs. No statistically significant correlations were found between the human monitoring data and PCP concentrations in wood or dust or the stated complaints.

[Evaluation of wood preservative pollutants of indoor air]

The evaluation of indoor pollution by wood preservatives and pesticides has been a matter of increasing interest for the past years. The present paper reviews actual knowledge. The so-called "wood preservative syndrome" is referred to. Basics and evaluation criteria concerning the investigation of external exposure (wood, dust, air) and human biomonitoring is summarized. Several substances, in particular pentachlorophenol, lindane and pyrethroids, and principle possibilities to decrease exposure are considered.

Pharmacodynamics of MDL 72974A: absence of effect on the pressor response to oral tyramine

MDL 72974A, a new irreversible selective inhibitor of monoamine oxidase (MAO)-B which is not metabolized to amphetamine-like compounds, is currently being developed for the treatment of Parkinson's disease. In this double blind, placebo controlled randomized study 24 healthy volunteers (n = 6/dose) received single oral doses of placebo, 1, 12 or 24 mg of MDL 72974A qd over two weeks. Sensitivity to orally administered tyramine was determined under fasting conditions before and after drug administration and the doses of tyramine yielding a 30 mmHg increase of SBP (PD30) compared. The 2-fold increase of tyramine sensitivity at end of treatment seen at all MDL 72974A dose levels, however, is within the variability range of the tyramine pressor response. MDL 72974A selectively inhibits MAO-B at doses up to 24 mg orally and has a favourable safety profile.

Pre- and postjunctional effects of phorbol 12-myristate-13-acetate in the mouse vas deferens

The protein kinase C stimulator phorbol 12-myristate-13-acetate (PMA) increased the release of noradrenaline from field-stimulated mouse vasa deferentia and antagonized the inhibitory effect of xylazine and FK 33-824. The mechanical response to field stimulation was not modified by PMA in unpretreated vasa, but the contractility was partly restored when the stimulation-response curve had been depressed by xylazine or FK 33-824. In contrast, PMA decreased the contractile response to exogenous noradrenaline and bethanechol. A similar but smaller reduction was obtained with 1,2-dioctanoyl-sn-glycerol. In vasa depolarized by KCl, PMA and verapamil reduced the amplitude of contractions elicited by CaCl2. Only the effect of verapamil could be reversed by the calcium ionophore A 23187, while the effect of PMA was greatly attenuated in muscles pretreated with ouabain. Phorbol 12-myristate-13-acetate-4-O-methylether was ineffective in all experiments. These results suggest that PMA increases noradrenaline release (prejunctional effect) and decreases vasal contractility (postjunctional effect) by activation of protein kinase C.

Negative chronotropic but no antiarrhythmic effect of (+)- and (-)-naloxone in rats and guinea pigs

STUDY OBJECTIVE

The aim was to investigate the antiarrhythmic effects of (+)- and (-)-naloxone in various arrhythmia models in vivo.

DESIGN

Naloxone (1-40 mg.kg-1), naltrexone (20-40 mg.kg-1), or standard antiarrhythmic drugs (quinidine, lignocaine, phenytoin, (+)-sotalol) were injected intravenously. Ventricular extrasystoles were then elicited by infusion of either ouabain (guinea pigs) or aconitine (rats), or by electrical stimulation (guinea pigs).

EXPERIMENTAL MATERIAL

Male Wistar rats and guinea pigs (n = 6-10) were used. Arterial blood pressure and ECG were recorded continuously.

MEASUREMENTS AND MAIN RESULTS

Naloxone and naltrexone decreased the heart rate. The effect of naloxone was not stereospecific and is apparently not mediated by opioid receptors. Naloxone had no influence on ouabain induced arrhythmias or fibrillation threshold in guinea pigs. The appearance of aconitine induced extrasystoles was accelerated by 20 mg.kg-1 (-)-naloxone but delayed by 40 mg.kg-1. No effects were seen with (+)-naloxone or (-)-naltrexone.

CONCLUSIONS

The results show that naloxone does not possess prominent antiarrhythmic properties.

Pre- and postjunctional effects of N-ethylmaleimide in the isolated mouse vas deferens

The influence of N-ethylmaleimide (NEM) on contractions due to exogenously applied noradrenaline and bethanechol and on the inhibitory effects of clonidine, of the enkephalin derivative, FK 33-824, and 2-chloroadenosine (2-CLA) on field stimulation-response curves and [3H]noradrenaline [( 3H]NA) release was studied in the isolated mouse vas deferens. Exposure to NEM (60 microM: 10 min) caused a 30% reduction of the maximal contraction due to NA but nearly abolished the response to bethanechol. NEM partially reversed the depression of the pulse width-response curves by clonidine and FK 33-824 but was without effect with 2-CLA. The contractions evoked by stimulation frequencies above 20 Hz were depressed by NEM both in presence and absence of the agonists. NEM diminished the inhibition of the stimulation-evoked release of [3H]NA by the three agonists. The prejunctional effect of NEM was markedly influenced by the stimulation parameters. These findings support the suggestion that the inhibition mediated by alpha 2-adrenoceptors, mu- and P1-receptors in the mouse vas deferens is NEM-sensitive and possibly transmitted by a pertussis toxin-sensitive G-protein.

The field-stimulated vas deferens of the streptozotocin-diabetic mouse: effects of prazosin, alpha, beta-methylene ATP, and variation of stimulation parameters

The question of diabetic neuropathy was studied in the field-stimulated isolated vas deferens of the mouse. The animals were treated with either buffer or streptozotocin (170 mg/kg i.v.) 2 or 4 weeks, respectively, beforehand. Stimulus-response relationships were tested by variation of frequency (VF) at constant pulse width and by variation of pulse width (VP) at constant frequency. The adrenergic twitch component was eliminated by prazosin (1 microM) and the purinergic component by alpha, beta-methylene ATP (MeATP, 10 microM). The diabetes did not alter the muscular contractility (tested with KCl) and left the twitch-inhibiting effects of prazosin and MeATP unchanged, thereby revealing no difference in susceptibility between noradrenergic and purinergic mechanisms. However, in diabetic vasa, the maximal effectiveness of stimulation was decreased with VF but not VP, whereas the sensitivity of intramural neurons (50% effective frequency or pulse width, respectively) was unchanged with VF and reduced with VP. This may suggest that the diabetic neuron release less transmitter (VF), which can be compensated for by the activation of less sensitive neurons (VP). Actually, the uptake of 3H-noradrenaline into the (4 weeks-) diabetic vas was normal but the stimulation-induced fractional release of tritium was decreased by 26%. It is concluded that a sympathetic neuropathy occurred in the vas deferens of the streptozotocin-diabetic mouse.

Noradrenergic, purinergic, and cholinergic transmission in the mouse vas deferens: influence of field-stimulation parameters, reserpinization, 6-hydroxydopamine and 4-aminopyridine

In the field-stimulated mouse vas deferens the twitch inhibiting potency of prazosin (1 microM) and alpha,beta-methylene ATP (MeATP, 10 microM) was studied, using two types of stimulation-response curves, (a) variation of frequency from 3 to 100 Hz at a constant pulse width of 0.1 ms and (b) variation of pulse width from 0.04 to 0.8 ms at a constant frequency of 15 Hz. Prazosin and MeATP reduced the twitch response by eliminating the noradrenergic and purinergic component, respectively. After the combined application of both compounds a small third twitch component remained that was most prominent at high frequencies. Reserpinization reduced the effect of prazosin but enhanced that of MeATP and increased the cholinergic component. 6-Hydroxydopamine enhanced the effects of prazosin and MeATP to the same extent, but left the cholinergic component intact. In vasa pre-loaded with [3H]-noradrenaline, field stimulation induced a larger release of tritium at high frequency and short pulse duration (100 Hz, 0.1 ms) than at lower frequency and long pulse duration (15 Hz, 0.3 ms). Prazosin (1 microM) augmented both the spontaneous and the stimulation-induced overflow of tritium, whereas MeATP (10 microM) had only a negligible negative effect on the outflow of label. In conclusion, the twitch contraction of the mouse vas deferens has a small cholinergic component in addition to the noradrenergic and purinergic components. Adrenergic and purinergic transmission seem not to run strictly in parallel: the purinergic component dominates during stimulation at low frequency and long pulse duration, and after reserpinization; 4-aminopyridine enhances the adrenergic mechanism more than the purinergic one.

Failure of coffee to inhibit the pharmacodynamic activity of morphine in vivo

High doses of caffeine-containing as well as decaffeinated instant coffee neither inhibited morphine-induced analgesia in mice nor the morphine-induced fall of blood pressure, heart rate and respiratory rate in rats. On the contrary, caffeine-containing coffee even enhanced the analgesic effects of morphine in mice. Coffee thus does not exhibit opiate-antagonizing activity in the whole organism in vivo. The very weak morphine-antagonistic efficacy of coffee powder in the myenteric plexus-longitudinal muscle preparation from the guinea pig ileum is of no practical importance.

Importance of frequency and pulse with in field stimulation of the mouse vas deferens: different behaviour of twitch-inhibiting drugs

The effect of six twitch-inhibiting drugs on the stimulus-response relationship in the field-stimulated mouse vas deferens was compared by means of stimulus response curves which were obtained in two ways, that is, variation of frequency at constant pulse width and variation of pulse width at constant frequency. The twitch-inhibiting potency (in the range of maximal twitch responses) differed with the type of stimulation in a way permitting two groups of substances to be defined: group A (tetrodotoxin, procaine, verapamil) was more effective on frequency-response curves and group B (FK 33-824, clonidine, nifedipine) on pulse-width response curves; the latter applied also to subnormal calcium concentrations in the bath solution. The results suggest that the effect of inhibitory drugs on the field-stimulated vas of the mouse varies greatly with the type of field stimulation.