An attempt at localizing adenylate cyclase in rat calvaria. Influence of sodium fluoride and parathyroid hormone

Protein kinase A regulates the disposition of Ca2+ which enters the cytoplasmic space through store-activated Ca2+ channels in rat hepatocytes by diverting inflowing Ca2+ to mitochondria

The roles of a trimeric GTP-binding regulatory protein, protein kinase A and mitochondria in the regulation of store-activated (thapsigargin-stimulated) Ca2+ inflow in freshly-isolated rat hepatocytes were investigated. Rates of Ca2+ inflow were estimated by measuring the increase in the fluorescence of intracellular fura-2 following the addition of extracellular Ca2+ (Ca2+o) to cells incubated in the absence of added Ca2+o. Guanosine 5'-[gamma-thio]-triphosphate (GTP[S]) and AlF4(-) inhibited the thapsigargin-stimulated Ca2+o-induced increase in cytoplasmic free Ca2+ concentration ([Ca2+]c) and this inhibition was prevented by the Rp diastereoisomer of adenosine 3',5'-(cyclic)phosphoro[thioate]. cAMP, forskolin and glucagon (half-maximal effect at 10 nM) mimicked inhibition of the thapsigargin-stimulated Ca2+o-induced increase in [Ca2+]c by GTP[S], but had little effect on thapsigargin-induced release of Ca2+ from intracellular stores. Azide and carbonyl cyanide p-trifluoromethoxyphenylhydrazone inhibited the thapsigargin-stimulated Ca2+o-induced increase in [Ca2+]c in the presence of increased cAMP (induced by glucagon). In contrast, Ruthenium Red markedly enhanced the thapsigargin-stimulated Ca2+o-induced increase in [Ca2+]c in both the presence and absence of increased cAMP (induced by forskolin and dibutyryl cAMP). It is concluded that, in hepatocytes, protein kinase A regulates the disposition of Ca2+, which enters the cytoplasmic space through store-activated Ca2+ channels, by directing some of this Ca2+ to the mitochondria. The idea that caution should be exercised in using observed values of Ca2+o-induced increase in [Ca2+]c as estimates of rates of agonist-stimulated Ca2+ inflow is briefly discussed.

Electron-microscopic cytochemical localization of adenylate cyclase activity in the myoepithelial cells of the lactating mouse mammary gland

Adenylate cyclase activity was localized in the lactating mouse mammary gland using an ultrastructural histochemical technique. Reaction product was deposited on the plasma membrane of the myoepithelial cells adjacent to the secretory epithelium. No reaction product was encountered on the secretory epithelium. These findings suggest that the presence of cAMP, previously biochemically documented in lactating mammary gland, is mainly connected with myoepithelial cellular activity. The asymmetrical distribution of adenylate cyclase activity suggests that cAMP is involved in the intercellular communication between the secretory and myoepithelial cells and that the secretory epithelium takes part in the regulation of the contraction of myoepithelial cells.

Cytochemical localization of adenylate cyclase activity in rat bone marrow

The localization of adenylate cyclase (AC) in rat bone marrow was studied at the ultrastructural level using a cytochemical technique with adenosine triphosphate (ATP) as substrate. The strongest precipitate occurred around cytoplasmic membranes of cells of granulocytic lineage. Around cells of erythrocytic lineage, as well as megakaryocytes, lymphocytes and the plasma cells, the granules resulting from the cytochemical reaction revealed various degrees of density. The region within the bone marrow tissue where the cells manifested an increased reaction product was called 'reaction fields'. Most often the 'reaction fields' were formed by maturing cells of the granulocytic and erythrocytic lineages, surrounding the reticular cells. The reaction precipitate was also apparent around the advential and endothelial cells of the sinuses. Mature cells migrating from the bone marrow space to the sinus lumen also showed an intensified reaction product. The causes of such localization of AC were discussed.

Electrophysiological properties of osteoblastlike cells from the cortical endosteal surface of rabbit long bones

The mean transmembrane potential of cultured osteoblastlike cells isolated from the cortical endosteal surface of rabbit long bones was -16.9 +/- 0.64 mV (n = 335). Elevation of potassium concentration in medium caused a decrease in potential. As the external concentration of potassium reached 15 mmol/liter and above, there was a linear relationship between the potassium concentration in log scale and the membrane potential with a slope of -13 mV per 10-fold change in external potassium concentration. Dibutyryladenosine 3',5'-cyclic monophosphate, parathyroid extract, hydrocortisone, and sodium fluoride all depolarized the membrane of osteoblast-like cells after both short (1-2 h) and long (24 h) exposures at suitable doses, whereas calcitonin and prostaglandin E2 hyperpolarized the membrane after long exposures. The Na+, K+ and Cl- concentrations of cultured osteoblastlike cells were 0.538, 0.984, and 0.358 mmol/g protein or 52.6, 96.3, and 35.0 mmol/liter cell water, respectively. The protein content of these cells was 8.18 +/- 0.6 g/100 g cells and the water content was 83.7 g/100 g cells. The above-mentioned chemical and hormonal preparations in doses that produced significant changes in the membrane potential of these cultured cells did not alter their electrolyte or protein contents 24 h after exposure. Intracellular pH of cultured osteoblastlike cells as determined by [14C]-dimethyloxazolidine-2,4-dione and 3H2O averaged 7.03 +/- 0.11 when the pH of culture medium was maintained at 7.4. Calculations based on the values for the membrane potential and the electrolyte concentrations observed in this study indicate that Na+, and H+, and Cl- are actively transported out of the cells and K+ into the cells.

Ultrastructural demonstration of endogeneous peroxidase activity in mammalian epidermis

With the diaminobenzidine method, endogenous peroxidase activity was demonstrated in the nuclear envelope and in the endoplasmic reticulum of non-keratinized keratinocytes and Langerhans cells of the epidermis of the newborn mouse, adult guinea pig and man. In the guinea pig all non-keratinized layers of keratinocytes showed this enzyme activity, whereas in the two other species examined peroxidase activity was limited to the suprabasal layers. The most pronounced activity was found in the Langerhans cells. The melanocytes were negative. With the same method, cytochrome c/cytochrome oxidase activity could be localized in the mitochondria of all epidermal cells of mouse and man, but not in the guinea pig.

Multiple localizations of adenylate cyclase in rat hippocampus. A histochemical study

A new method for the histochemical demonstration of adenylate cyclase activity, introduced and biochemically tested by Poeggel et al. (1981 a), was employed in nervous tissue. Using this method a multiple pattern of activity was detectable. Activity occurs in nervous as well as glial elements. Biochemical results and physiological conclusions could be confirmed by ultrahistochemical visualization of adenylate cyclase activity in nervous tissue. The specificity of the reaction is controlled by a number of variations of the incubation methods.