Quantitative histochemical investigations of semipermeable membrane techniques for the assay of acid phosphatase in skeletal muscle. I. Meijer's method

A lysosome-targeted near-infrared fluorescent probe for imaging of acid phosphatase in living cells

Fluorescent probes for the detection of acid phosphatases (ACP) are important in the investigation of the pathology and diagnosis of diseases. We reported a lysosome-targeted near-infrared (NIR) fluorescent probe SHCy-P based on a novel NIR-emitting thioxanthene-indolium dye for the detection of ACP. The probe showed a long wavelength fluorescence emission at λ_em = 765 nm. Due to the ACP-catalyzed cleavage of the phosphate group in SHCy-P, the probe exhibited high selectivity and sensitivity for the 'turn-on' detection of ACP with a limit of detection as low as 0.48 U L^-1. The probe SHCy-P could also be used to detect and image endogenous ACP in lysosomes. In light of these prominent properties, we envision that SHCy-P will be an efficient optical imaging approach for investigating the ACP activity in disease diagnosis.

Macrophages in the small intestinal muscularis externa of embryos, newborn and adult germ-free mice

Previously, we demonstrated the presence of a constant and regularly distributed macrophage population of ramified cells in the intestinal muscle layers of smaller rodents. The function of these resident macrophages under normal conditions remains unknown. Histochemistry, immunohistochemistry and electron microscopy were applied to the muscularis externa of 15- and 17-day-old embryos, 2-day-old mice, adult germ-free and conventional mice. Since lipopolysaccharides (LPS) activates macrophages and inflammation affects gut motility, LPS-treated mice were also included in the study. Two macrophage antibodies, F4/80 and 2F8 were used to demonstrate the presence of macrophages in the muscle layers. The localization was confirmed by electron microscopy. In contrast to conventional adult mice, the muscle layers in embryos, newborn and germ-free adult mice were devoid of class II MHC antigen reactive cells. The acid phosphatase reaction and antibodies directed towards a lysosomal protein (Lamp-2) were used in order to verify other activation markers. None of these showed specific staining of the muscularis macrophages. Only LPS-treated adult mice showed iNOS-positive cells in whole mounts. We conclude that the characteristic organization and distribution of muscularis macrophages in adult mice are also present in embryos, newborn and germ-free mice and thus develop independently of foreign antigens. Further, these macrophages are truly resident and appear to have differential responses to exogene stimuli.

Changes in acid phosphatase activity in rat liver after ischemia

The effect of ischemia on the stability, i.e. the permeability of the lysosomal membrane of rat liver has been studied using quantitative histochemical analysis of acid phosphatase activity. Ischemia in vitro was performed for 0-240 min at 37 degrees C and ischemia in vivo for 60 min was followed by 1, 5, 24 and 48 h of reperfusion. Acid phosphatase activity was demonstrated in cryostat sections using naphthol AS-BI phosphoric acid as substrate and polyvinyl alcohol was added to the incubation medium to counteract diffusion phenomena. Ischemia in vitro up to 240 min did not affect the localization nor the total activity of acid phosphatase activity. After 60-min ischemia in vivo followed by 1-h reperfusion distinct areas showed decreased acid phosphatase activity. A further decrease in activity was observed after 5 h reperfusion. Final reaction product generated by acid phosphatase activity was rather diffusely distributed in border zones between normal and damaged tissue after 24 and 48 h of reperfusion following 60 min ischemia in vivo. It is concluded that not ischemia itself but rather reperfusion affects the stability of the lysosomal membrane due to the occurrence of oxygen-derived free radicals and/or imbalanced Ca2+ concentration. Restoration of the blood flow causes leakage of acid phosphatase from the lysosomes into the cytoplasm of liver parenchymal cells and from there to the blood.

Acid phosphatase activity in soleus and plantaris muscle fibres of normal and dystrophic hamsters. A quantitative histochemical study

The activity of acid phosphatase in skeletal muscle fibres of the plantaris and soleus of normal and dystrophic male hamsters was quantified using a histochemical post-coupling semipermeable membrane technique. Although the absolute levels of activity were found to vary widely from one animal to another, the ratio of the mean activities in the two muscles in each animal was virtually constant. In normal muscles, the ratio was about 0.73 and in dystrophic muscles, about 0.77. The activity in plantaris muscle fibres was always significantly lower than that in the corresponding soleus fibres, and in normal fibres compared to dystrophic ones. Another difference was that in normal fibres the mean activity declined to a constant level in mature animals older than about 3 months. In contrast, the activity in dystrophic muscles appeared to fall exponentially throughout life. The functional significance of these findings is discussed.

Acid phosphatase activity of human gingival fibroblasts measured using a simultaneous coupling semi-permeable membrane technique

Acid phosphatase activity has been measured in cultured human gingival fibroblasts using a validated histochemical simultaneous coupling semi-permeable membrane technique. The histochemical reaction was linear over a three hour incubation period and had a pH optimum of 5.0. The activity was not increased by prior exposure to hypotonic acetate buffer and was inhibited by fluoride and molybdate but not by formaldehyde. These results indicate that the semi-permeable membrane technique described may be used for observing and measuring acid phosphatase activity in cultured fibroblasts. From results obtained using inhibitors, it appears that in these cells most of the acid phosphatase observed is lysosomal. The absence of any activation of activity following pre-incubation with hypotonic buffer indicates that the method is not suitable for monitoring lysosomal membrane function.

Quantitative histochemical investigations of semipermeable membrane techniques for the assay of acid phosphatase in skeletal muscle. IV. A post-coupling technique

A post-coupling semipermeable membrane technique for determining the activity of acid phosphatase in sections of skeletal muscle has been developed and investigated for its reproducibility and validity. Cryostat sections of unfixed muscle mounted on dry dialysis membranes are first incubated for 1-4 at 37 degrees C on a gelled medium containing 4 mM naphthol AS-BI phosphate buffered at pH 5. They are next transferred to another gel containing only hexazotised Pararosanaline and incubated for a further 30 min. Finally, they are treated with 70% ethanol, dried in air, and mounted. The final reaction product (FRP) deposited within muscle fibres is mostly distributed as a fine reticular network, tentatively identified as sarcoplasmic reticulum. Large FRP "granules' of the kind observed with Meijer's simultaneous coupling membrane technique are not formed. The method is reproducible and valid in terms of several working criteria. For example, the mean absorbance of the FRP at its absorption maximum increases linearly with incubation time; and in model sections containing various amounts of a subcellular fraction rich in acid phosphatase, the mean absorbance after a constant incubation time is proportional to the enzyme concentration. FRP is formed at approximately twice the rate it is deposited in the simultaneous coupling method. The most important advantage of the post-coupling method over the simultaneous coupling method is that the inhibition of the enzyme by coupling reagents is avoided.

Quantitative histochemical investigations of semipermeable membrane techniques for the assay of acid phosphatase in skeletal muscle. III. A modified simultaneous coupling technique

Meijer's semipermeable membrane technique for acid phosphatase was modified by treating sections immediately after incubation with 70% ethanol for 30 min at room temperature instead of with formalin. The modification improved the validity of the technique considerably, by stabilising the specific final reaction product formed in presumed enzyme-containing sites. The modified technique thus seems promising for assaying the activity of acid phosphatase in sections of skeletal muscle.

Quantitative histochemical investigations of semipermeable membrane techniques for the assay of acid phosphatase in skeletal muscle. II. Non-specific reactions in control sections

The absorbances of skeletal muscle fibres at 530 nm in control sections of either fresh or boiled tissue, incubated according to Meijer's semipermeable membrane technique for acid phosphatase, increase linearly with incubation time. Moreover, the absorbances continue to increase even after the incubation has been terminated by immersion of the sections in formalin. The comparatively weakly absorbing yellow reaction product originally formed is transformed with 24 h of mounting the sections into a strongly absorbing purple material with an absorption maximum at 570 nm. The original yellow product seems to be hexazotised Pararosanaline adsorbed onto tissue proteins. The formation of the purple product can be prevented by treating control sections immediately after incubation with 70% ethanol for 30 min at room temperature in place of formalin. Ethanol stabilises the yellow non-specific reaction product but does not extract it from tissue sections. The ethanol treatment thus seems useful for improving the validity of Meijer's technique.