The distribution of cholinesterase types in mammalian tissues

The use of buccal swabs as a minimal-invasive method for detecting effects of pesticide exposure on enzymatic activity in common wall lizards

Habitat loss and environmental pollution are among the main causes responsible for worldwide biodiversity loss. The resulting species and population declines affect all vertebrates including reptiles. Especially in industrialized countries, pollution by agrochemicals is of remarkable importance. Here, habitat loss has historically been associated with expansion of agriculture. Species persisting in such environments do not only need to cope with habitat loss, but more recently, also with chemical intensification, namely pesticide exposure. In this study, we examined effects of different fungicide and herbicide applications on the common wall lizard (Podarcis muralis) in grape-growing areas. We used three enzymatic biomarkers (GST, GR, AChE) and for the first time saliva from buccal swabs as a minimal-invasive sampling method for detection. Our results demonstrate absorption of substances by lizards and effects of pesticide exposure on enzymatic activities. Our findings are in accordance with those of previous laboratory studies, although samples were retrieved from natural habitats. We conclude that buccal swabs could become a useful tool for the detection of pesticide exposure in reptiles and have the potential to replace more invasive methods, such as organ extraction or cardiac puncture. This is an important finding, as reptiles are non-target organisms of pesticide applications, and there is a strong need to integrate them into pesticide risk assessments.

Enzymatic activity in the M band

Experiments which combined histochemistry and electron microscopy were performed in studying the sites of enzymatic hydrolysis of thiolacetic acid in the presence of lead ions in diaphragmatic and cardiac muscle. It was found that in these striated muscles the electron opaque, final product of the histochemical reaction (PbS) was discretely deposited on the swelling of the thick elemental filaments that occurs at the M band. Additional sites of enzymatic activity occurred in mitrochondria and in round sarcoplasmic bodies. A reaction, probably non-enzymatic, also occurred in contraction bands in the area of the Z bands and in the sarcoplasmic reticulum. To ascertain the enzymatic nature of the reaction and to define the enzyme involved, control experiments were carried out and the effect of various esterase inhibitors was assayed. It is suggested that the M band enzyme is a cholinesterase, but the enzymes in the mitochondria and the sarcoplasmic bodies that hydrolyze the substrate appear to be different. A possible role of the M band enzyme is discussed.

CHOLINESTERASE IN DENERVATED END PLATES AND MUSCLE FIBRES

Parallel studies were made of cholinesterase activities and localizations in denervated rat and rabbit gastrocnemius muscle. Koelle's histochemical reaction was used for demonstrating the localization of cholinesterases. Enzyme activities in whole sliced muscle were measured by electrometric titration. The Cartesian ampulla-diver technique was used for cholinesterase activity determinations in end plate regions or in small pieces of the muscle fibre itself. No changes in the activity of cholinesterases (ChE) were found in the whole denervated muscle which would account for its chemical supersensitivity. The ChE distribution pattern was changed so that the end plate region became less active in the denervated muscle than in the normal one. The decrease in ChE activity in the end plates seems to be largely compensated for by an increase of this enzyme elsewhere in the muscle. A possible connection between the spatial spread of cholinesterase activity and the enlargement of the acetylcholine-sensitive surface is discussed.

THE LOCALIZATION OF CHOLINESTERASE ACTIVITY IN RAT CARDIAC MUSCLE BY ELECTRON MICROSCOPY

A method has been developed for localizing sites of cholinesterase activity in rat cardiac muscle by electron microscopy. The method utilizes thiocholine esters as substrates, and is believed to be dependent on the reduction of ferricyanide to ferrocyanide by thiocholine released by enzymatic activity. The ferrocyanide thus formed is captured by copper to form fine, electron-opaque deposits of copper ferrocyanide, which sharply delineate sites of enzymatic activity at the ultrastructural level. Cholinesterase activity in formalin-fixed heart muscle was localized: (a) in longitudinal elements of the sarcoplasmic reticulum, but not in the T, or transverse, elements; and (b) in the A band, with virtually no activity noted in the M band, or in the H zone. The I band was also negative. No activity was detected in the sarcolemma, or in invaginations of the sarcolemma at the level of the Z band. The perinuclear element of the sarcoplasmic (endoplasmic) reticulum was frequently strongly positive. Activity at all sites was completely abolished by omitting the substrates, or by inhibition with eserine 10(-4)M and diisopropylfluorophosphate 10(-5)M. Eserine 10(-5)M completely inhibited reaction in the sarcoplasmic reticulum, and virtually abolished that in the A band. These observations, together with the use of the relatively specific substrates and suitable controls to eliminate non-enzymatic staining, indicate that cholinesterase activity was being demonstrated. The activity in rat heart against different substrates was that of non-specific cholinesterases, in accordance with biochemical data. The activity in the A band was considered to be probably due to myosincholinesterase. It is proposed that the localization of cholinesterases in myocardium at the ultrastructural level should be taken into account in considering the possible functions of these myocardial enzymes, and it is hoped that knowledge of their localization will open up new avenues of approach in considering their physiological role in myocardium, which at present is not definitely known.

Butyrylcholinesterase activity in the developing auditory brainstem, the choroid plexus and the pituitary of the perinatal rat

The butyrylcholinesterase activity in the vasculature of the brain, choroid plexus, and pituitary, was studied histochemically in rats during postnatal days 1, 7, 14, 21 and 28. The brainstem auditory nuclei were used for comparison of vessels at different ages. We found intense butyrylcholinesterase activity in all intraparenchymal blood vessels, especially capillaries, in all ages. In the meningeal vessels, activity was especially prominent in 1 and 7 day old animals when the perineural meninges was relatively thick. In the pituitary, reaction for the enzyme was found in nonvascular elements, especially in the intermediate and posterior lobes. Vessels of the choroid plexus were associated with punctate regions of butyrylcholinesterase activity. These results do not support the suggestion of a major role for butyrylcholinesterase in the blood-brain barrier.

Secretion of acetylcholinesterase by a mouse hepatocyte X rat liver cell hybrid culture

A hybrid cell line (E-2) that secretes the enzyme acetylcholinesterase (AChE) has been prepared. The E-2 cell was the product of a fusion between primary mouse hepatocytes and a chemically transformed rat liver cell line (FRL), neither of which expresses AChE activity. The enzyme was determined to be AChE on the basis of its susceptibility to inhibition by BW284c51 but not by iso-OMPA, as well as its substrate specificity. Although the secreted enzyme was salt soluble and its activity not modified by the addition of the nonionic detergent, Triton X-100, the activity of the cellular enzyme (derived from homogenates of E-2 cells) was greatly enhanced in the presence of the detergent.

Activity, molecular forms, and cytochemistry of cholinesterases in developing rat diaphragm

Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) were studied in the diaphragm of early postnatal rats, using radiometric determination of enzyme activities, velocity sedimentation for separation of molecular forms, and electron microscopic cytochemistry to localize enzymes. AChE activity did not change significantly during the first 2 months after birth. The level of 16 S AChE was high at early stages, but decreased to adult levels between days 19 and 32 after birth. In newborn and 8-day-old rats, 16 S and 13 S AChE were present in both endplate and extrajunctional muscle. In newborn muscle, BuChE activity was higher than AChE activity, but decreased 6-fold by day 32. Newborn muscle contained 16 S, 10 S, and 4 S BuChE. The principal form throughout development was 4 S BuChE, but all forms diminished as total BuChE activity decreased with maturation. At early postnatal neuromuscular junctions, end product of both AChE and BuChE was present in the cleft, as well as in Schwann cells. More Schwann cells wee present in early stages than in later stages, and this might account for part of the later decrease of BuChE activity measured biochemically.

Tissue choline studied using a simple chemical assay

An enzymatic-radioisotopic assay was used to measure free choline in unextracted tissue. The lowest concentration of free choline in any tissue studied was present in human cerebrospinal fluid (mean, 5.7 microM; range, 1.8 + 31.2 microM). A postmortem increase in concentration of free choline occurred in blood (0.2 nmol/min.ml), kidney (13 nmol/min.g) and liver (22 nmol/min.g) of mice. The concentration of free choline in these tissues was estimated by extrapolation to be 5, 77, and 29 nmol/g (or ml), respectively. Several treatments were found to increase the concentration of free choline. For example, intraperitoneal administration of choline or 2-amino-2-methyl-propanol (a choline oxidase inhibitor) induced an increase in the level of choline i blood, kidneys, liver, and brain of mice, and administration of 2-dimethylaminoethanol (deanol) caused an increase in kidney and liver choline. The level of choline in blood was increased when rats were treated orally with either antibiotics or esters of choline such as phosphorylcholine, glycerylphosphorylcholine, laroylcholine, or propionylcholine. The results show that the concentration of free choline may be regulated by intestinal metabolism, availability of esterified precursors, and activity of enzymes that metabolize choline.

Radiolabeled benzoylcholine derivatives as possible myocardial-imaging agents

Two radioiodinated analogs of benzoylcholine were investigated as possible myocardial-imaging agents. O-([2-125I]Iodobenzoyl)-choline and N-([2-125I]iodobenzoyl)cholamine were prepared by nucleophilic substitution of sodium [125I]iodide for stable iodine in O-(N,N]dimethylaminoethyl)-2-iodobenzoate and N-(N',N'-dimethylaminoethyl)-2-iodobenzamide, respectively, and by methylation with methyl iodide. The in vivo distribution of each compound in mice was determined as a function of time. Favorable heart-to-blood and heart-to-lung ratios were obtained with N-([2-125I]iodobenzoyl)cholamine.

Haemodynamic responses to antagonism of pancuronium and alcuronium block

Using non-invasive methods, haemodynamic responses to antagonism of pancuronium (Pc) and alcuronium (Ac) block were compared in patients anaesthetized with thiopental-N2O-fentanyl and undergoing minor surgery. Neuromuscular block (90%) was maintained with Pc in 10 patients and Ac in 10 patients. After surgery, atropine 0.015 mg kg-1 and neostigmine 0.03 mg kg-1 (AN) were given simultaneously. The rate of reversal of the block was equal in the two groups. Between 4 and 16 min after AN, the decrease of heart rate (HR) was more pronounced in patients who had received Pc. The mean of the lowest HR was 43.2 beats min-1 in the Pc group, compared with 62.0 beats min-1 in the Ac group. The bradycardia was associated with a moderate decrease in arterial pressure in patients treated with Pc. However, due to an increase in stroke volume, mean cardiac output (CO) was not lower in the Pc group. Some patients treated with Pc developed a temporary nodal rhythm after AN and this was associated with a considerable decrease in CO. It is concluded that, in spite of marked bradycardia during antagonism of Pc block, circulation is well maintained, provided that sinus rhythm is present.

Mechanisms of neurohumoral regulation of heart function in aging

Changes in hemodynamics and myocardial contractile capacity following the stimulation of extracardial nerves and administration of various doses of acetylcholine, norepinephrine, propranolol, phentolamin, atropine, serpasil and benzohexonium were studied in albino rats, rabbits and cats of various age. The shifts in cardiac acetylcholine and norepinephrine content and the activity of some enzymes of their catabolism were determined as well. Functional changes were compared with the structural shifts in intramural nervous system. In old animals there was a rise in threshold of voltage, which induced threshold reaction at stimulation of n. vagus and n. sympaticus and there was a change in heart sensitivity to acetycholine and norepinephrine, propranolol, atropine, serpasil and benzohexonium. A relationship was shown between age changes in nervous regulation of heart and transmitter metabolism. The intensity of acetylcholine and norepinephrine synthesis was decreased in old age, the transmitter metabolism in various parts of the heart was not uniformly altered, the sensitivity of epicardial chemoreceptors to nicotine, veratrum, acetylcholine was increased. The reflexes from cardiac mechanoreceptors were diminished.

The effect of cholinesterase inhibitors on the antimuscarinic effect of hemicholinium-3 (HC-3) in the rat

The effect of hemicholinium-3 (HC-3) on responses of the rat isolated bladder and ileum to acetylcholine and carbachol was investigated in the absence and presence of a number of anticholinesterases. Responses of the bladder to acetylcholine were potentiated by DFP, edrophonium, BW284C51 and physostigmine but were unaffected by the specific butyrylcholinesterase inhibitor iso-OMPA. Responses to carbachol were not potentiated by the anticholinesterases. HC-3 (1.7 X 10(-4) M) inhibited responses to carbachol without affecting those to acetylcholine. In the presence of physostigmine or DFP responses to acetylcholine were inhibited by HC-3 but no such inhibition was observed in the presence of BW284C51, edrophonium or iso-OMPA or a combination of the latter two anticholinesterases. Responses to carbachol were also inhibited to a greater extent in the presence of DFP. In the ileum, responses to acetylcholine were increased in the presence of DFP, edrophonium and physostigmine but were unaffected by iso-Ompa. responses to carbachol were not increased by any of the anticholinesterases. HC-3 (2.8 X 10(-4) M) inhibited responses to both acetylcholine and carbachol in the ileum and the degree of inhibition was not significantly altered by the presence of any of the anticholinesterases used. Although a weak anticholinesterase, HC-3 was also found to decrease the inhibitory action of physostigmine on the hydrolysis of acetylcholine by homogenates of rat ileum. A similar effect was noted with DFP but not with edrophonium. The results obtained do not support a prejunctional action for HC-3 in antagonizing responses to carbachol. It is concluded that in addition to an inhibitory action on the post-junctional muscarinic receptor HC-3 may interfere with the anticholinesterase activity of some cholinesterase inhibitors such as physostigmine and DFP but not edrophonium.

Investigation of central cholinergic mechanisms in the conscious mouse

1. An investigation of central cholinoceptors in the mouse has been made by injecting cholinomimetic drugs into the cerebral ventricles and seeing how their effects were modified by prior administration of atropine-like substances and other drugs.2. Carbachol or oxotremorine injected in small doses intracerebroventricularly into conscious mice caused hypothermia, gross tremor and a variety of parasympathomimetic effects including lachrymation and salivation. Acetylcholine injected in this way was active only in much larger doses.3. Methacholine and pilocarpine also caused a variety of parasympathomimetic effects after intracerebroventricular injection but virtually no hypothermia or tremor.4. Nicotine injected intracerebroventricularly caused mild hypothermia, fine tremor but no parasympathomimetic effects.5. Atropine-like drugs, tricyclic antidepressants and amphetamine antagonized the hypothermia induced by intracerebroventricular carbachol or oxotremorine.6. The sites of action of the atropine-like drugs are in the brain; those of the tricyclic antidepressants and amphetamine are in the periphery probably on heat generating beta-adrenoceptor mechanisms.7. It is concluded that the atropine sensitive cholinoceptors in the brain vary in their sensitivities to cholinomimetic drugs, other than acetylcholine, and may exist in isoreceptor forms.8. Peripheral atropine sensitive cholinoceptors may also exist in isoreceptor forms.