Biomedical subjects

I Litosch

Publications and source records attributed to I Litosch.

28 records · Page 2Linked to original sources

PubMed1984

Synergistic activation of rat hepatocyte glycogen phosphorylase by A23187 and phorbol ester.

The combination of 1.6 microM 4 beta phorbol, 12 beta myristate, 13 alpha acetate (PMA) and 1 microM A23187 produced a five-fold greater stimulation of rat hepatocyte glycogen phosphorylase activity than was seen with PMA alone. Vasopressin activation of glycogen phosphorylase was comparable to that seen with PMA plus A23187. Glycogen phosphorylase activity due to PMA plus A23187 was increased significantly after 30 sec, maximal at 120 and sustained at elevated levels for 240 sec. In contrast, activation due to vasopressin was maximal at 30 sec followed by a decrease. The addition of PMA 5 min prior to the A23187 abolished the synergism between these two agents. These data are compatible with the hypothesis that diacylglycerol and Ca2+ synergistically increase glycogen phosphorylase activity in rat hepatocytes.

Animals↗

PubMed1984

Phosphoinositide breakdown in blowfly salivary glands.

In blowfly salivary glands, 5-hydroxytryptamine stimulated a rapid and sustained loss of [3H]inositol, [32P]phosphatidylinositol, phosphatidylinositol 4-phosphate, and phosphatidylinositol 4,5-bisphosphate. There was a corresponding increase in labeled inositol phosphates. In the absence of Ca2+, 5-hydroxytryptamine stimulated a rapid but transient loss of labeled phosphatidylinositol 4,5-bisphosphate. By 5 min, the amount of labeled phosphatidylinositol 4,5-bisphosphate recovered to control values. The divalent ionophore A23187 stimulated loss of labeled phosphatidylinositol 4,5-bisphosphate and increased the amount of labeled phosphatidylinositol. In homogenates, Ca2+ stimulated phosphatidylinositol 4,5-bisphosphate breakdown but not phosphatidylinositol breakdown. These results suggest that hormone-stimulated breakdown of labeled phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate occurs through a phospholipase C and is relatively independent of extracellular Ca2+. There is also a Ca2+-activated conversion of phosphatidylinositol 4,5-bisphosphate to phosphatidylinositol.

Animals↗

PubMed1983

Rapid changes in hepatocyte phosphoinositides induced by vasopressin.

Vasopressin stimulated a 40% decrease in [32P]phosphatidylinositol 4,5-bisphosphate and a 15% decrease in [32P]phosphatidylinositol within 30 s of addition to hepatocytes prelabeled for 60 min with 32P. In hepatocytes prelabeled with [3H]inositol for 60 min, vasopressin produced 20% breakdown of phosphatidylinositol and 33% breakdown of phosphatidylinositol 4,5-bisphosphate within 30 s. There was a 40% increase in total phosphatidylinositol 4,5-bisphosphate within 30 s of vasopressin addition. Breakdown of phosphatidylinositol accounted for disappearance of 95% of the inositol lipid label. In hepatocytes from rats labeled in vivo with [3H]inositol, vasopressin stimulated 10% loss of labeled phosphatidylinositol. Loss of [32P]phosphatidylinositol due to vasopressin was followed by reincorporation of label to levels greater than control while 32P reuptake into phosphatidylinositol 4,5-bisphosphate did not exceed control values. With in vitro [3H]inositol-labeled hepatocytes, loss of label from the phosphoinositides was followed by reuptake of tritium label to control levels. In hepatocytes labeled in vivo with [3H]inositol, reuptake of [3H]inositol label did not occur. These data indicate that the hormone-sensitive pool of hepatocyte phosphoinositides can be labeled by both in vitro and in vivo procedures. Vasopressin induces a rapid decrease of labeled phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate within 30 s.

Animals↗

PubMed1983

Hormonal regulation of phosphatidylinositol breakdown.

Cyclic AMP and Ca2+ are intracellular mediators of hormone action. Catecholamines interact with beta adrenoceptors to activate adenylate cyclase or with alpha 2 adrenoceptors to inhibit adenylate cyclase. Alpha 1 adrenoceptor activation results in elevation of cytosol Ca2+ and an increased breakdown of phosphatidylinositol. In blowfly salivary glands, 5-hydroxytryptamine (5-HT) interacts with beta type receptors resulting in adenylate cyclase activation while alpha type receptors are involved in phosphatidylinositol breakdown and elevation of cytosol Ca2+. The link between Ca2+ mobilization and phosphatidylinositol breakdown remains to be established but breakdown of the receptor-regulated pool of phosphatidylinositol is not secondary to the rise in Ca2+. Direct addition of 5-HT to cell-free homogenates of blowfly salivary glands results in activation of phosphatidylinositol breakdown in the absence of Ca2+. In rat liver plasma membrane preparations, vasopressin increases phosphatidylinositol breakdown in the absence of Ca2+ or cytosol if deoxycholate is present. The data do not indicate whether hormone activation increases the availability of substrate to enzymatic hydrolysis or activates phospholipase C. However, they demonstrate that hormones directly accelerate phosphatidylinositol breakdown.

Animals↗

PubMed1982

Forskolin as an activator of cyclic AMP accumulation and secretion in blowfly salivary glands.

Forskolin is a diterpene that activates adenylate cyclase in a variety of mammalian cells. In addition of forskolin to blowfly salivary glands increased cyclic AMP accumulation and salivary secretion. There was a small increase in transepithelial movement of labelled Ca2+. Forskolin did not induce breakdown of labelled phosphatidylinositol or inhibit the stimulation of phosphatidylinositol breakdown caused by 5-hydroxytryptamine. These data indicate that forskolin can mimic all the effects of 5-hydroxytryptamine on salivary-gland secretion that have been attributed to cyclic AMP.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1982

Regulation of adenylate cyclase and cyclic AMP phosphodiesterase by 5-hydroxytryptamine and calcium ions in blowfly salivary-gland homogenates.

Salivary-gland homogenates contain 5-hydroxytryptamine-stimulated adenylate cyclase. Half-maximal stimulation was obtained with 0.1 microM-5-hydroxytryptamine in the presence of added guanine nucleotides. Gramine antagonized the stimulation of cyclase caused by 5-hydroxytryptamine. In the presence of hormone, guanosine 5'-[gamma-thio]triphosphate produced a marked activation of adenylate cyclase activity. Stimulation of adenylate cyclase by forskolin or fluoride did not require the addition of guanine nucleotides or hormone. In the presence of EGTA, Ca2+ produced a biphasic activation of cyclase activity. Ca2+ at 1-100 microM increased activity, whereas 2000 microM-Ca2+ inhibited cyclase activity. The neuroleptic drugs trifluoperazine and chlorpromazine non-specifically inhibited adenylate cyclase activity even in the absence of Ca2+. The cyclic AMP phosphodiesterase activity in homogenates was not affected by Ca2+ or exogenous calmodulin. This enzyme was also inhibited by trifluoperazine in the absence of Ca2+. These results indicate that Ca2+ elevates adenylate cyclase activity, but had no effect on cyclic AMP phosphodiesterase of salivary-gland homogenates.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1982

5-HT-stimulated arachidonic acid release from labeled phosphatidylinositol in blowfly salivary glands.

In blowfly salivary glands, breakdown of phosphatidylinositol has been linked to the activation of hormone-sensitive Ca2+ channels. Addition of 5-hydroxytryptamine to blowfly salivary glands stimulated the breakdown of phosphatidylinositol prelabeled with 32P or [3H]arachidonic acid. This was associated with a transient accumulation of [3H]arachidonic-labeled diglyceride. There was no appreciable effect of 5-hydroxytryptamine on breakdown of phosphatidylethanolamine or phosphatidylcholine labeled with 32P or [3H]arachidonic acid, indicating that phosphatidylinositol was the immediate source of diglyceride. Extracellular Ca2+ was necessary for [3H]arachidonic acid but not 32P loss from phosphatidylinositol. Addition of arachidonic acid to salivary glands did not stimulate salivary gland secretion or 45Ca flux. In contrast, 5-hydroxytryptamine stimulated both salivary gland secretion and 45Ca flux. These results indicate that, although [3H]arachidonic acid is incorporated into phosphatidylinositol and its release from this phospholipid is increased by 5-hydroxytryptamine, the liberated arachidonic acid does not stimulate salivary gland secretion or 45Ca flux.

Animals↗

PubMed1982

Forskolin as an activator of cyclic AMP accumulation and lipolysis in rat adipocytes.

Forskolin increased cyclic AMP accumulation in isolated adipocytes and markedly potentiated the elevation of cyclic AMP due to isoproterenol. In adipocyte membranes, forskolin stimulated adenylate cyclase activity at concentrations of 0.1 microM or greater. Forskolin did not affect the EC50 for activation of adenylate cyclase but did increase the maximal effect of isoproterenol. Neither the soluble nor particulate low-Km cyclic AMP phosphodiesterase activity was affected by forskolin. Low concentrations of forskolin (0.1-1.0 microM), which significantly elevated cyclic AMP levels, did not increase lipolysis, whereas similar increases in cyclic AMP levels due to isoproterenol elevated lipolysis. Forskolin did not inhibit the activation of triacylglycerol lipase by cyclic AMP-dependent protein kinase or the subsequent hydrolysis of triacylglycerol. Higher concentrations of forskolin (10-100 microM) did increase lipolysis. Both the increased cyclic AMP production and lipolysis due to forskolin were inhibited by the antilipolytic agents insulin and N6-(phenylisopropyl)adenosine. Hypothyroidism reduced the ability of forskolin to stimulate cyclic AMP production and lipolysis. These results indicate that forskolin increases cyclic AMP production in adipocytes through an activation of adenylate cyclase. Lipolysis is activated by forskolin but at higher concentrations of total cyclic AMP than for catecholamines.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1981

Effect of thyroid status on alpha- and beta-catecholamine responsiveness of hamster adipocytes.

It has been suggested that part of the increased beta-catecholamine responsiveness in hyperthyroid animals is due to a decrease in alpha-catecholamine action. The present results indicate that neither hyperthyroidism nor hypothyroidism altered the alpha 2-adrenergic inhibition of adenylate cyclase or the alpha 1-adrenergic stimulation of phosphatidylinositol turnover in adipocytes from the white adipose tissue of hamsters. No effect of hyperthyroidism was found on the Kd for binding of [3H]dihydroergocryptine or the number of binding sites in membranes prepared from hamster adipocyte tissue. The stimulation of cyclic AMP due to beta-catecholamines was enhanced in adipocytes from hyperthyroid hamsters, as was lipolysis. However, in adipocytes from hyperthyroid hamsters the maximal stimulation of cyclic AMP due to isoproterenol, ACTH or epinephrine plus yohimbine, as seen in the presence of adenosine deaminase and theophylline, was less than in adipocytes from euthyroid hamsters. The activation of adenylate cyclase by isoproterenol was the same in membranes from hyperthyroid as compared to those from euthyroid hamsters in the absence or presence of guanine nucleotides. These data suggest that thyroid status has little effect on alpha-catecholamine action by enhances the activation of lipolysis by beta-catecholamine agonists.

Adipose Tissue↗

PubMed1980

Sickle red cell calcium metabolism: studies on Ca2+-Mg2+ATPase and Ca-binding properties of sickle red cell membranes.

Sickle (Hb SS) red cells, preloaded with 45Ca by reversal of hemolysis, exhibit an incomplete 45Ca extrusion, retaining approximately four times more 45Ca than normal cells. Studies indicated that neither the reduction in Hb SS cell Ca2+-Mg2+ ATPase activity (84% of normal) nor the activation of Ca2+-Mg2+ ATPase by calmodulin was sufficiently different from normal cells to attribute a major role to the calcium pump in 45Ca retention. These results suggested that 45Ca retention may reflect an alteration in the calcium-binding properties of Hb SS cell membranes. Low-affinity calcium-binding (freely dissociable) was similar in normal and Hb SS cell membranes. However, the total calcium bound with high-affinity (tightly bound) was four-to-five times greater in Hb SS cell membranes than in normal membranes. These results are compatible with the hypothesis that Hb SS cell 45Ca retention reflects an exchange of a fraction of the total 45Ca with a tightly bound calcium pool, larger in Hb SS cell membranes than in normal membranes. A comparable degree of red cell 45Ca retention, which did not correlate with the reticulocyte population, was observed in other chronic anemic states. These findings suggest that the increased high-affinity calcium binding by the membrane may be a consequence of cellular changes induced by the anemic condition.

Adolescent↗