Cyclic GMP System in epidermis: I. Effect of ischemia

Ionophore A23187 stimulates arachidonic acid release and cyclic GMP accumulation in pig epidermis

We studied the effect of Ionophore A23187 (A23187) on phospholipid degradation and the accumulation of cyclic GMP in pig epidermis. A23187 stimulated the release of AA, probably partially through the activation of phospholipase A2. A23187 also stimulated the accumulation of epidermal cyclic GMP, but the activity of cyclic GMP-dependent phosphodiesterases was not altered. Mepacrine, an inhibitor of phospholipase A2, inhibited the A23187-stimulated accumulation of cyclic GMP. The results suggest that A23187 stimulates the accumulation of epidermal cyclic GMP by a calcium-dependent process which also requires products of phospholipid degradation.

"Ischemic" rise of epidermal cyclic AMP is a beta-adrenergic adenylate cyclase-dependent process

The endogenous level of epidermal cyclic AMP does not remain constant but increases rapidly and transiently after removal of the tissue; this is known as the "ischemia" effect. UVB-irradiated epidermis which shows increased beta-adrenergic response revealed an increased ischemia effect, while psoriatic involved epidermis which shows decreased beta-adrenergic response revealed a decreased ischemia effect. Because of the similar rise-and-fall pattern between the ischemia effect and the beta-adrenergic response, the mechanism of the ischemia effect was investigated, especially in terms of the beta-adrenergic relationship. The ischemic rise of epidermal cyclic AMP was well preserved after 6 h pretreatment at 4 degrees C, and, following the pretreatment, the skin markedly increased its cyclic AMP level by the 37 degrees C treatment with 1 mM isobutylmethyl xanthine. The addition of propranolol or cimetidine at the time of 37 degrees C treatment (following the 4 degrees C pretreatment) had no effect on the ischemia effect; both skin groups markedly increased their cyclic AMP levels to an extent similar to that of the control skin. However, the addition of propranolol at the time of both preincubation (at 4 degrees C) and incubation (at 37 degrees C) markedly decreased the ischemic rise of cyclic AMP. Similar treatment by cimetidine had no effect on the ischemia effect. There was no significant difference in cyclic AMP phosphodiesterase activities among skin groups by propranolol or cimetidine pretreatment. These results indicate that the so-called ischemic rise of epidermal cyclic AMP is actually the beta-adrenergic adenylate cyclase-dependent process. Our results also indicate that the magnitude of the "ischemic" rise of cyclic AMP is generally parallel to the beta-adrenergic responsiveness of epidermis.

Agents that activate cyclic AMP-dependent protein kinase inhibit explant culture growth and mitotic activity

Epidermal cells contain 4 separate surface receptors which are linked to adenylate cyclase. Activation of any one of these receptors leads to the accumulation of cAMP within the cell which in turn leads to the activation of cAMP-dependent protein kinase. The levels of cAMP accumulation within the cell caused by the 4 activators are not the same. Epinephrine, histamine, adenosine, and prostaglandins of the "E" series cause easily measurable concentrations of cAMP within 5 min of exposure. Prostaglandin F2 alpha causes only a small nonsignificant increase. Similarly, 2 phosphodiesterase inhibitors, which inhibit the breakdown of cAMP formed within the cell, differ in their ability to accumulate cAMP when cells are exposed to these agents alone. Isobutylmethylxanthine causes a measurable increase in cAMP, while theophylline, a weak inhibitor of phosphodiesterase, gives a nonsignificant increase in cAMP. Recently, experiments have shown that agents that give only slight increases in cAMP by biochemical measurements, that is, prostaglandins F2 alpha and theophylline, are equally able to activate protein kinase within the cell. Since activation of protein kinase is the only mechanism for an increase in cAMP to have a physiologic effect, all of these agents that do activate protein kinase should cause physiologic effects. Using an explant culture system, we show in this paper that this supposition is correct and that all agents that activate protein kinase do result in inhibition of mitotic activity regardless of whether or not they are able to raise cAMP to a level that can be biochemically measured as being significantly different from the baseline value.

Phospholipase A2 activity modulates "ischemic effect" in pig skin

The level of cyclic AMP in the epidermis rapidly increase within 15 min after separation from the in vivo condition. This phenomenon is the so-called "ischemic effect." In order to elucidate the possible mechanism of the ischemic effect, the effects of melittin and mepacrine on the ischemic condition of the skin were studied. Melittin, a stimulator of phospholipase A2, lessened the increase of cyclic AMP, while mepacrine, an inhibitor of phospholipase A2, potentiated the increase of cyclic AMP during the ischemic condition. The overall results suggest that phospholipase A2 may play an important role in the induction of the ischemic condition through membrane alteration.

Decreased accumulation of cyclic adenosine 3',5'-monophosphate in "ischemic" skin after 12-0-tetradecanoyl-phorbol-13-acetate treatment

The effect of 12-0-tetradecanoyl-phorbol-13-acetate (TPA) on cyclic adenosine 3',5'-monophosphate (cyclic AMP) level in adult mouse skin in response to ischemia was examined. The incubation of skin pieces in a buffered salts medium at 37 degrees C resulted in a rapid accumulation of cyclic AMP. In mouse skin pieces maximum accumulation (about 6 times the basal level) occurred after 2 min incubation and was followed by a rapid decline in the cyclic AMP level. This "ischemic" rise in epidermal cyclic AMP was greatly reduced if skin was used 16 hr after a single application of 17 nmoles of TPA. The effect of TPA on cyclic AMP accumulation in response to ischemia was first observed at 1 hr after TPA treatment and was maximal at 4 hr. The lack of "ischemic" response in TPA-treated skin was not related to an increase in the activity of cyclic AMP phosphodiesterase after TPA application. In addition, the accumulation of cyclic AMP in skin in response to both ischemia and exposure to isoproterenol, adenosine, histamine, or prostaglandin E2 (PGE2) was not observed in skin treated with the tumor promoter TPA.

The effect of ischemia on cyclic adenosine 3',5'monophosphate accumulation in mouse skin

The incubation of adult mouse skin pieces in a buffered salts medium at 37 degrees C led to a rapid accumulation of cyclic adenosine 3'5-monophosphate (cyclic AMP) in the tissue. In mouse skin maximum accumulation occurred after 2 min incubation; levels reverted to near control levels after a further 7 min incubation. the increase in cyclic AMP contents of the skin pieces was probably not due to the release of materials which activate adenylate cyclase after binding to cellular receptors. Thus, cyclic AMP accumulation was unaffected by the inclusion of alpha- or beta-adrenergic antagonists, or by the pretreatment of adult mouse skin with indomethacin (an inhibitor of prostaglandin synthetase). Furthermore, adenosine, a known activator of epidermal adenylate cyclase, could not be detected in the incubation medium. The functional integrity of epidermal adenylate cyclase was maintained during the cyclic AMP accumulation in response to ischemia. Thus, adenosine, histamine, isoproterenol and prostaglandin E2 (PGE2) augmented the cyclic AMP response. Cyclic AMP accumulation at 37 degrees C was not observed in newborn mouse skin; this lack of cyclic AMP accumulation was probably not due to increased activity of low affinity cyclic AMP phosphodiesterase in newborn mouse skin.

Activation of cAMP-dependent protein kinase in epidermis by the compounds which increase epidermal cAMP

Pig epidermal slices were incubated with various compounds which increased epidermal cAMP (adenosine 3',5'-monophosphate), and the change in cAMP-dependent protein kinase activity ratio was studied by the method of Cherrington et al (J Biol Chem 251:5209-5218, 1976) with modification. Epinephrine (5 x 10(-5) M), histamine (10(-4) M) and adenosine (10(-3) M), potent agonists of epidermal adenyl cyclase, fully activated the protein kinase (PK) during an incubation of 30 to 45 seconds, that was much shorter than that required for maximal cAMP accumulation under the same conditions (5 min). With such a brief stimulus, the epidermal cAMP-PK system did not become refractory and responded to repeated stimuli. Prostaglandin E2 (PGE2) and isobuthylmethylxanthine (IBMX) and ethanol only partially activated the enzyme. Prostaglandin F2 alpha (PGF2 alpha) and theophylline which were much less effective in increasing epidermal cAMP, activated the enzyme to the same extent as PGE2 and IBMX respectively. These results suggest that protein kinase activation takes place in response to a cAMP increase in small locus of the cell. Such an increase in cAMP can be very small or even not measurable when measured as total cAMP in the tissue homogenate. Also, increases above this level may not be physiologic. It is concluded that measurement of cAMP-dependent protein kinase activity ratio is a more direct and more sensitive way to study the effect of compounds which act through cAMP mediated mechanisms.

Epidermal cyclic GMP is increased in psoriasis lesions

Cyclic GMP levels in epidermis of normal subjects and of psoriatic patients were measured with a highly sensitive radioimmunoassay method. Technical improvements for the assay are 2-fold: (1) skin samples were frozen in vivo before biopsy and local injection of any anesthetic was avoided to overcome ischemia effect which could lower cyclic GMP artificially; (2) epidermis was microdissected to avoid contamination of dermis and keratin layers. The results show that on a per mg tissue dry weight basis the cyclic GMP levels are about 200 fmol in the involved lesional epidermis and 70 fmol in the uninvolved or normal epidermis. Similarly increases in the cyclic GMP levels in the lesional epidermis are observed when the data are expressed either on a DNA or protein basis. The cyclic GMP level in normal epidermis from nonpsoriatic subjects is the same as that in the uninvolved epidermis of psoriasis patients.

Immunohistochemical localization of cyclic nucleotides in guinea pig lip

The cellular localization of cAMP and cGMP in the guinea pig lip was investigated with an indirect immunofluorescence technique. cAMP was distributed both in cell membranes and cytoplasmic elements with coarse and granular intranuclear fluorescence, while cGMP was localized in nuclear sites including nuclear membranes as well as cell membranes and cytoplasm. In the basal portion, both cAMP and cGMP fluorescence was weaker in cytoplasm and cell membranes than seen in the upper portion.