Ultrastructural localization and differentiation of membrane-bound ATP utilizing enzymes including adenyl cyclase in normal and psoriatic epidermis

Transmembrane cation fluxes and fatty acid composition of erythrocytes in psoriatic patients

Cation transport systems and lipid composition of erythrocyte membrane were studied in 27 psoriatic patients and in 34 healthy individuals. Whereas intracellular Na and K content, Na- and K-passive permeability and Li-Na countertransport of psoriatics did not show any statistical difference from normals, the Na/K ATPase pump activity was significantly higher and Na-K cotransport was significantly lower. Membrane lipid composition of psoriatics was different from normals: an increase in arachidonic acid and in unsaturated (poly- and total unsaturated) fatty acid content was found. A positive correlation was demonstrated between unsaturated/saturated fatty acid ratio and Na/K ATPase pump activity. These results demonstrate an alteration of erythrocyte Na/K ATPase pump and Na-K cotransport in psoriasis. These alterations of cation transport are associated with a perturbation of membrane fatty acid composition which appears a widespread phenomenon in cells of psoriatic patients.

Red blood cell sodium and potassium fluxes in psoriatic patients

Psoriasis might be a widespread membrane disorder. Therefore, the red blood cell sodium, potassium and lithium outward fluxes (through Na-K-ATPase, Na-K-Cl co-transport, Li-Na countertransport and passive permeability), as well as the Na and K content, were studied in 31 psoriatic patients and 23 normal controls. A significant increase in intracellular potassium content, in the maximal velocity of the Na-K ATPase and of Na-K-Cl co-transport as well as in the outward passive permeability for Na were found in the psoriatic patients compared with controls. On the contrary, no differences were observed in sodium content, Li-Na countertransport and passive potassium permeability between the two groups. These results are compatible with a selective increase in inward, as well as outward, membrane permeability to sodium, which is compensated for by increased activity of the Na-K pump, and of the outward Na-K-Cl cotransport with a secondarily increased erythrocyte potassium content. They indicate that the red blood cell might be a useful model for the study of membrane transport in psoriatics.

A histochemical study on the vitamin D synthesis into the epidermis

Using a suitable histochemical method vitamins D and 7-dehydrocholesterol could be shown into the epidermis of several mammal species. As the histochemical method used is able to discriminate vitamins D and 7-dehydrocholesterol from cholesterol and its esters, the sites where these vitamins were synthesized within the epidermis layers could be established. Vitamins D and 7-dehydrocholesterol were found into the epidermis in the same sites where cholesterol and its esters take place, such as: the keratinizing cell thick membrane and the stratum spinosum and stratum granulosum keratinocytes cytoplasm. Inside the keratinocyte cytoplasm vitamin D shows a granular pattern and appears weakly bound to proteins. The reactivity of such granules seems to be partially blocked as could be shown by an hydrolysis accomplished previously. After the hydrolysis reactive vitamin D was also found inside the epidermis intercellular space. The results suggest that vitamin D is synthesized into the cytoplasm of stratum spinosum and stratum granulosum keratinocytes, where it appears weakly bound to proteins. Afterwards it reaches the intercellular space, where its synthesis is accomplished and it becomes firmly protein-bound losing its histochemical reactivity. However, after a suitable hydrolysis the histochemical reactivity could be recovered. From the intercellular spaces vitamin D could take 2 fates: It was partially incorporated on the keratinizing cell thick membrane out surface and eliminated by means of the epidermis exfoliation. It was partially absorbed after passing across the basement membrane. On the other hand, the vitamin D placed inside the stratum spinosum and stratum granulosum keratinocytes cytoplasm become incorporated on the inner surface of the keratinizing cell thick membrane. The relationship between vitamin D biosynthesis and the epidermis lamellar bodies was discussed.

Erythrocyte membrane phosphorylation in untreated and in etretinate-treated psoriatic patients

Levels of phosphorylation were decreased in bands 2 to 2.1, 2.9 to 3 and 4.5 to 4.8 of erythrocyte membranes from psoriatic patients compared with control values. In addition, higher than control levels of 32P were incorporated into a new polypeptide band (mol.wt. 18-20,000 daltons) of red cell membranes from patients. Uptake of 32P by these bands returned towards normal after the patients received oral etretinate treatment. These results suggest there is a generalized plasma membrane defect in psoriasis and that etretinate may affect the metabolism of red cell membrane proteins.

Altered erythrocyte membrane phosphorylation in psoriasis

Autophosphorylation by [gamma-32P]ATP of erythrocyte membranes from controls, psoriatic patients and patients with skin disorders other than psoriasis was compared by polyacrylamide gel electrophoresis. Compared with controls, membranes from psoriatic patients showed significantly less 32P incorporation in the band 2 region (nomenclature of Fairbanks et al., 1971). In addition, psoriasis and some of the other skin diseases examined displayed decreased phosphorylation in the region of bands 2.9-3 and 4.5-4.8. A new polypeptide band in the 18-20,000 dalton region was also observed in the diseases examined. Altered epidermal plasma membranes have been implicated in the pathogenesis of psoriasis, and our findings suggest the defective plasma membranes may be a generalized phenomenon in this disorder.

Characterization of alpha- and beta-adrenergic agonist stimulation of adenylate cyclase activity in human epidermal keratinocytes in vitro

Adrenergic receptors are responsible for selective recognition and binding of catecholamines and may in turn have an effect on epidermal cell growth and maturation via adenosine-3',5'-monophosphate (cAMP). Using endogenous catecholamines and drugs specific for alpha- and beta-receptor subtypes, we have characterized the adrenergic receptor coupled to adenylate cyclase in cultured human epidermal keratinocytes. The relative potency order of stimulation of adenylate cyclase was: isoproterenol greater than epinephrine much greater than norepinephrine. The predominant adrenergic receptor is of the beta 2-subtype, as also confirmed by use of the selective antagonists propranolol, butoxamine, and atenolol. No evidence of alpha-adrenergic receptor mediation of adenylate cyclase was noted with the alpha 2-specific agonist, clonidine. Phenylephrine, the alpha 1-specific agonist, affected cAMP formation but this response could not be totally inhibited with prazosin, suggesting an unknown mechanism of action. Human keratinocytes retained the same beta-adrenergic receptor potency order properties throughout growth and maturation.

Adenylate cyclase activity during growth and maturation of keratinocytes: comparison of two methods of study

The adenylate cyclase activity of primary cultures of guinea-pig ear keratinocytes was studied at different times by challenge with various agonists after labelling of ATP by exposure of the cells to [3H]-adenine. The [3H]-cAMP (cyclic adenosine-3',5-monophosphate) formed was assayed by scintillation counting. In other experiments, cells were exposed to the equivalent amount of unlabelled adenine, challenged and cAMP was then assayed by radioimmunoassay. These absolute amounts were compared to [3H]-cAMP levels expressed as percentage conversion of [3H]-ATP. Comparison of the two methods suggested that the use of the prelabelling method would result in underestimation of cAMP formed. It was found that the response of the enzyme to different agonists changed with the length of time of the cells in culture.

Plasma membranes in psoriatic cells. A freeze-fracture study

A freeze-fracture study of affected and unaffected psoriatic skin has demonstrated the presence of marked modification of the plasma membrane in the psoriatic lesion. In the lower layers of the epidermis, an increase of membrane associated particles was observed in many keratinocytes, possibly representing the morphological intramembranous equivalent of changes in the outer cell membrane demonstrated with cytochemical techniques. Furthermore, in the malphighian layer, numerous gap junctions have been found, which may be interpreted as a phenomenon compensating the uncontrolled proliferation, and may represent a point of differentiation between cell proliferation in psoriasis and neoplasia. This technique confirmed the poor tendency to adhesion of keratinocytes in extrajunctional areas, which had already been shown by other morphological techniques.

Thin-layer chromatography of phospholipid components of normal and psoriatic epidermis

The phospholipid pattern of human epidermis from 23 psoriatic patients and from 14 healthy individuals has been determined using lipid thin-layer chromatography. An increased amount of total phospholipids and statistically significant differences in some phospholipid components were found in psoriatic patients as compared to healthy controls. These abnormalities may be related to the altered architecture of the plasma membranes and their surface coats observed in psoriatic keratinocytes.

Electron microscopic cytochemical demonstration of adenyl cyclase activity in psoriatic epidermis

Isoproterenol and sodium fluoride stimulated adenyl cyclase activity was detected in epidermal tissue from 2 patients with untreated psoriasis by an electron microscopic cytochemical technique. Adenyl cyclase activity was present on the outer surface of the cell membranes, predominantly in the basal cells and in the 4-5 lower Malpighian cell layers, while the superficial layers, stratum granulosum and stratum corneum showed no activity. The precipitates (lead-PPi complexes) after isoproterenol stimulation were larger and fewer in number than those seen after sodium fluoride stimulation. Isoproterenol stimulation was abolished by propranolol. Neither the uninvolved epidermis from the 2 patients with psoriasis nor the normal skin from 2 volunteer individuals showed any difference from the psoriatic epidermis.

[Disturbed distribution of surface glycoconjugates of the plasma cell membrane in psoriasis. Cytochemical detection using the alcianblue-lanthan-reaction (author's transl)]

Lanthanum has been used as a tracer for the intercellular space and the surface coats in different epithelia including human epidermis, however, lanthanum compounds may or may not penetrate into skin specimes and reaction product may or may not be present in the intercellular space. After treatment with alcian blue prior exposure to lanthanum the trilaminar plasma membrane was more regularly stained and a thin coat of reaction product corresponding to superficial glycoconjugates outlined the cell surface and filled the narrow intercellular space in normal epidermis. In psoriatic epidermis the quantity of superficial membrane-bound glycoconjugates was rather reduced, their distribution and compartmentalization was profoundly changed and the outer leaflet of the trilaminar plasma membrane was not always clearly seen, having a "moth-eaten appearance" in some places. These findings show once more that alterations of the cell membranes and their surface architecture are present in psoriasis. They may play a major role in the pathogenesis of the disease, influencing the activities of membrane-bound enzymes and the flow of the epidermal growth control mechanism. The glycocalyx may serve in this mechanism as an accumulator of energy rich compounds or as a receptor site of membrane-bound ezymes. According to our views it represents a "ground substance" of epidermal origin, which controls the social behaviour of the keratinocytes in tissue.

[Lack of beta-adrenergic stimulation of membrane bound adenyl cyclase in psoriasis as compared to normal epidermis (author's transl)]

Glucagon and beta-adrenergic compounds such as 1-isoproterenol stimulated the low activity of an ATP-utilizing enzyme located on the cell membranes of normal keratinocytes. Addition of beta-antagonist propranolol to the incubation medium prevented the stimulatory effect of 1-isoproterenol. We considered, therefore, the reaction product being due to epidermal membrane-bound adenyl cyclase activity. In psoriatic epidermis the basal adenyl cyclase activity was low, similar to normal epidermis, however, glucagon and 1-isoproterenol failed to stimulate the enzyme activity in psoriasis under the same conditions. It seems, therefore, that the beta-adrenergic-cAMP cascade as a regulatory epidermal control mechanism of induced proliferation is ineffective in this disease.