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Biomedical subjects

H Rasmussen

Publications and source records attributed to H Rasmussen.

At least 145 records · Page 8Linked to original sources
PubMed1987

The effects of bombesin on polyphosphoinositide and calcium metabolism in Swiss 3T3 cells.

Bombesin, a peptide mitogen for a variety of cell types, acts as a typical Ca2+-mobilizing hormone in Swiss 3T3 fibroblasts. At its mitogenic concentrations (1-25 nM), bombesin stimulates polyphosphoinositide turnover, i.e. breakdown of phosphatidylinositol 4,5-bisphosphate and a concomitant increase in inositol phosphates in a time- and dose-dependent manner. In particular, bombesin induces an initial transient increase in inositol 1,4,5-trisphosphate concentration, followed by an increase in the concentration of inositol 1,3,4-trisphosphate. Also, within 30 s of bombesin addition, the mass of 1,2-diacylglycerol nearly doubles and remains at this level for up to 60 min. Intracellular [Ca2+] measurements with a photoprotein, aequorin, demonstrate that bombesin stimulates a transient rise in cytosolic free Ca2+ concentration. A mobilization of Ca2+ from an intracellular pool is observed as a dose-dependent, transient increase in 45Ca2+ efflux from prelabeled cells, both in the presence and absence of extracellular Ca2+. Bombesin also induces a sustained increase in Ca2+ influx rate and stimulates 3-O-methyl-D-glucose transport across the plasma membrane. These composite results indicate that the mitogenic effect of bombesin is mediated through an activation of the Ca2+ messenger system.

3-O-Methylglucose↗
PubMed1987

Measurement of cytoplasmic free Ca2+ concentration in bovine tracheal smooth muscle using aequorin.

The cytoplasmic free Ca2+ concentration in bovine tracheal smooth muscle strips was measured using aequorin. Carbachol induces a rapid rise in aequorin luminescence, which reaches a peak within 1-2 min and then falls to a plateau level in 5-6 min. This plateau gradually declines but remains significantly above the base-line value after 2 h. The initial Ca2+ transient is due to Ca2+ mobilization from an intracellular caffeine-sensitive pool. The plateau appears to be due to Ca2+ influx. Histamine or 5-hydroxytryptamine (serotonin) also induce a Ca2+ transient followed by a plateau phase which is lower than that induced by carbachol. The isometric tension generated by either of these two agonists shows a gradual decline in contrast to the sustained plateau seen in the carbachol-induced contraction. Extracellular high K+ induces a dose-dependent increase in aequorin luminescence that is totally due to Ca2+ influx across the plasma membrane and is greatly inhibited by a Ca2+-channel antagonist, nimodipine. These results suggest that two temporally and spatially different Ca2+-dependent mechanisms are involved in carbachol-induced tracheal smooth muscle contraction.

Aequorin↗
PubMed1987

Calcium in the regulation of aldosterone secretion and vascular smooth muscle contraction.

A model of angiotensin II action has been developed in which the flow of information from cell surface to cell interior proceeds by two temporally distinct branches: a calmodulin branch largely responsible for initiating the response; and a C-kinase branch for sustaining it. There are at least two initial events: a prompt and sustained increase in calcium influx rate, and prompt hydrolysis of phosphatidylinositol 4,5-bisphosphate. The latter leads to the generation of water-soluble inositol 1,4,5-trisphosphate and lipid soluble diacylglycerol. The rise in inositol 1,4,5-trisphosphate concentration causes the redistribution of intracellular calcium, a transient rise in the calcium concentration in the cytosol, and the activation of calmodulin-dependent enzymes, including protein kinase(s). As a result, several cellular proteins are rapidly phosphorylated and initiate the cellular response. The rise in calcium and these initial phosphorylation events are transient, however, so that an additional mechanism is necessary to sustain the response. The rise in diacylglycerol content, along with the transient rise in cytosolic calcium, leads to a shift of the C-kinase from a calcium-insensitive to a calcium-sensitive, plasma membrane-associated form. In this location, the activity of C-kinase is regulated by the rate of calcium flux across the plasma membrane. As a result of the activity of the C-kinase, a second set of cellular proteins becomes phosphorylated, and these control the sustained phase of the response.

Adrenocorticotropic Hormone↗
PubMed1987

Measurement of cytoplasmic free Ca2+ concentration in rabbit aorta using the photoprotein, aequorin. Effect of atrial natriuretic peptide on agonist-induced Ca2+ signal generation.

Addition of norepinephrine, angiotensin II, or histamine leads to a transient rise in the cytoplasmic Ca2+ concentration ([Ca2+]i), as measured with aequorin, in rabbit aortic strips. Each induces a [Ca2+]i transient which peaks in 2 min and then falls either back to baseline (angiotensin II) or to a plateau (norepinephrine and histamine). The [Ca2+]i transient is due to the mobilization of Ca2+ from a caffeine-sensitive, intracellular pool. An elevation of [K+] to 35 mM leads to a monotonic sustained rise in [Ca2+]i which depends entirely on extracellular Ca2+, but an increase to 100 mM leads to a [Ca2+]i transient from the mobilization of intracellular Ca2+. Atrial natriuretic peptide does not alter basal [Ca2+]i nor inhibit the [Ca2+]i transient induced by either histamine or angiotensin II, but blocks that induced by norepinephrine, and blocks the plateau phase induced by either histamine or norepinephrine. The peptide inhibits the contractile response to all three agonists and to K+.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1987

Interactions of cholecystokinin and glucose in rat pancreatic islets.

The effects of sulfated cholecystokinin (CCK-8S) and glucose on insulin secretion and polyphosphoinositide (PPI) metabolism were studied in isolated rat islets. Both agonists stimulate PPI hydrolysis, inositol phosphate accumulation, 3H efflux from [3H]inositol-prelabeled tissue, and 45Ca efflux from prelabeled cells. However, the effects of CCK-8S on PPI metabolism are considerably greater than those of glucose. Furthermore, the effects of CCK-8S on PPI and Ca2+ metabolism are observed whether islets are incubated in either 2.75 or 7 mM glucose, but CCK-8S only stimulates insulin secretion (a biphasic response) when the higher glucose concentration is present. Addition of 1 microM forskolin to islets incubated in media containing 2.75 mM glucose does not influence basal insulin secretion but sensitizes the islets to the action of CCK-8S. In the presence of forskolin, CCK-8S induces a very marked first phase but no second phase of insulin secretion. We postulate that CCK-8S acts in this tissue via receptor-linked PPI hydrolysis, leading to an inositol trisphosphate-induced Ca2+ efflux. These receptor-mediated effects of CCK-8S are not altered either by the ambient glucose concentration or the cAMP content of the islets, but these two factors determine the responsiveness of the islets (in terms of insulin secretion) to a given CCK-8S signal.

Animals↗
PubMed1987

Protein kinase C in the regulation of smooth muscle contraction.

The cellular and molecular mechanisms underlying smooth muscle contraction are reviewed in the light of recent studies of smooth muscle ultrastructure and of the role of polyphosphoinositide turnover and protein kinase C function in smooth muscle contraction. A new model of smooth muscle contraction is proposed that differs radically from accepted views, particularly the latch bridge hypothesis, in terms of both Ca2+ messenger function and the molecular events underlying this process. A coordinate fibrillar domain model of contraction is proposed in which the initial and sustained phases of contraction are mediated by different cellular and molecular events. The initial phase of response is mediated by a rise in [Ca2+]c and the resulting calmodulin-dependent activation of both myosin light chain kinase and the dissociation of caldesmon from the actin-caldesmon-tropomyosin-myosin fibrillar domain. These events lead to an interaction between actin and the phosphorylated light chains of myosin just as in previous models. However, this initial phase is followed by a sustained phase in which a rise in [Ca2+]sm stimulates the plasma membrane-associated, Ca2+-sensitive form of protein kinase C that results in the phosphorylation of both structural and regulatory components of the filamin-actin-desmin fibrillar domain. These events underlie the tonic phase of contraction.

Adenosine Triphosphatases↗
PubMed1986

Carbachol-induced protein phosphorylation changes in bovine tracheal smooth muscle.

The changes in protein phosphorylation associated with bovine tracheal smooth muscle contraction were studied by labeling intact muscle strips with [32P]PO4(3-) and analyzing the phosphoproteins by two-dimensional gel electrophoresis. Among 20 to 30 phosphoproteins resolvable with the two-dimensional electrophoresis system, the phosphorylation of 12 proteins was reproducibly affected by treatment with carbachol, in a time-dependent manner. Five of these proteins have been identified as 20-kDa myosin light chain, caldesmon, synemin, and two isoelectric variants of desmin. The other 7 are low molecular weight (Mr less than 40,000) cytosolic proteins. One cytosolic protein and myosin light chain are quickly but transiently phosphorylated by carbachol, the peak of myosin light chain phosphorylation being at about 1 min after agonist addition. In contrast, both variants of desmin, synemin, caldesmon, and 5 cytosolic proteins are phosphorylated at varying rates and remain phosphorylated for the duration of carbachol action. These "late" phosphorylation changes occur simultaneously with the dephosphorylation of one cytosolic protein. These carbachol-induced phosphorylation changes, like the contractile response, appear to be calcium-dependent. The addition of 12-deoxyphorbol 13-isobutyrate, a protein kinase C activator, causes a dose-dependent, sustained contraction of tracheal smooth muscle which develops more slowly than that induced by carbachol. This contractile response is associated with the same protein phosphorylation changes as those observed after prolonged carbachol treatment. In contrast, forskolin, an adenylate cyclase activator and a potent smooth muscle relaxant, induces the phosphorylation protein 3 and one variant of desmin. These observations strongly suggest that different phosphoproteins may be mediators of tension development and tension maintenance in agonist-induced contraction of tracheal smooth muscle.

Animals↗
PubMed1986

Carbachol induces a rapid and sustained hydrolysis of polyphosphoinositide in bovine tracheal smooth muscle measurements of the mass of polyphosphoinositides, 1,2-diacylglycerol, and phosphatidic acid.

The effects of carbachol on polyphosphoinositides and 1,2-diacylglycerol metabolism were investigated in bovine tracheal smooth muscle by measuring both lipid mass and the turnover of [3H]inositol-labeled phosphoinositides. Carbachol induces a rapid reduction in the mass of phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-monophosphate and a rapid increase in the mass of 1,2-diacylglycerol and phosphatidic acid. These changes in lipid mass are sustained for at least 60 min. The level of phosphatidylinositol shows a delayed and progressive decrease during a 60-min period of carbachol stimulation. The addition of atropine reverses these responses completely. Carbachol stimulates a rapid loss in [3H]inositol radioactivity from phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-monophosphate associated with production of [3H]inositol trisphosphate. The carbachol-induced change in the mass of phosphoinositides and phosphatidic acid is not affected by removal of extracellular Ca2+ and does not appear to be secondary to an increase in intracellular Ca2+. These results indicate that carbachol causes phospholipase C-mediated polyphosphoinositide breakdown, resulting in the production of inositol trisphosphate and a sustained increase in the actual content of 1,2-diacylglycerol. These results strongly suggest that carbachol-induced contraction is mediated by the hydrolysis of polyphosphoinositides with the resulting generation of two messengers: inositol 1,4,5-trisphosphate and 1,2-diacylglycerol.

Animals↗
PubMed1986

Temporal patterns of protein phosphorylation after angiotensin II, A23187 and/or 12-O-tetradecanoylphorbol 13-acetate in adrenal glomerulosa cells.

The temporal patterns of protein phosphorylation in the adrenal glomerulosa cell were analysed by two-dimensional electrophoresis after stimulation with 10 nM-angiotensin II or various agents [10 nM-12-O-tetradecanoylphorbol 13-acetate (TPA), 50 nM-A23187, 1 microM-nitrendipine], administered singly or in combination. These patterns were compared with the temporal patterns of aldosterone secretion induced by the same agonists and antagonists. After 1 and 30 min of stimulation with angiotensin II, different patterns of protein phosphorylation were observed. A comparison of these patterns reveals that: the phosphorylation of only one protein was persistently enhanced during the continuous incubation with angiotensin II; the phosphorylation of five proteins was transiently enhanced (at 1 min but not 30 min); and the phosphorylation of three proteins did not occur at 1 min but was seen at 30 min. Addition of the phorbol ester TPA alone, which at 30 min is without effect in enhancing aldosterone production, has no effect on protein phosphorylation. The combined addition of TPA and the Ca2+ ionophore, A23187, which, like angiotensin II, evokes a sustained increase in aldosterone production, reproduced the temporal patterns of protein phosphorylation seen after angiotensin II action. Manipulations (A23187 alone, angiotensin II plus nitrendipine) which evoke only a transient rise in aldosterone production rate induce a transient rise in cellular protein phosphorylation. The 1 min patterns of phosphorylation seen after A23187 or combined angiotensin II and nitrendipine (a Ca2+ channel antagonist) are similar to those observed after 1 min of angiotensin II stimulation. These results suggest that, when angiotensin II acts, the initial cellular response is mediated by a different mechanism than that responsible for the sustained response.

Adrenal Glands↗
PubMed1986

Short term memory in the calcium messenger system. Evidence for a sustained activation of protein kinase C in adrenal glomerulosa cells.

If adrenal glomerulosa cells are treated with angiotensin II for a period of 20-30 min, their subsequent response to either a rechallenge with the same concentration of angiotensin II or treatment with BAY K 8644, a calcium channel agonist, differs from the responses of control cells. Perifusion of control cells with 10 nM-angiotensin II leads to an increase in aldosterone secretory rate from 44 +/- 7 to 166 +/- 9 pg/min per 10(6) cells, but perifusion of cells pretreated for a 20 min period with angiotensin II leads to an increase in secretory rate from 51 +/- 9 to 209 +/- 18 pg/min per 10(6) cells. Likewise, treatment of control cells with 10 nM-BAY K 8644 leads to no significant increase in aldosterone secretory rate, but treatment of previously exposed cells to angiotensin II leads to an increase in rate from 51 +/- 9 to 130 +/- 11 pg/min per 10(6) cells. This memory effect is time-dependent in two ways: cells must be exposed to angiotensin II for 20 min or more before it is apparent; the longer the time between removal of angiotensin II and the rechallenge, the less effect these agents have on aldosterone secretory rate. When cells are exposed to angiotensin II for 20 min and then treated with [Sar1,Ala8]angiotensin II, a competitive antagonist of angiotensin II action, the aldosterone secretory rate falls to basal with a half time of 5-7 min. If BAY K 8644 is added simultaneously with [Sar1,Ala8]angiotensin II, the secretory rate falls with a halftime of 35-60 min. BAY K 8644 increases Ca2+ influx rate to the same extent in the presence or absence of [Sar1,Ala8]angiotensin II, and does not alter the effect of either angiotensin II or [Sar1,Ala8]angiotensin II on the production of inositol tris-, bis-, or mono-phosphate. In cells treated with 10 nM-angiotensin II for either 20, 30 or 45 min, the extent of phosphorylation of four cellular proteins is increased. If cells treated for 20 min with angiotensin II are then treated with [Sar1,Ala8]angiotensin II, and examined 15 min later (35 min), there is no longer an increase in the extent of phosphorylation of any of the four proteins. If such cells are then treated with 10 nM-BAY K 8644 and re-examined 5 min later (40 min), all four patients show an increase in the extent of phosphorylation.(ABSTRACT TRUNCATED AT 400 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1986

C-kinase activation prolongs Ca2+-dependent inactivation of K+ currents.

Voltage-dependent K+ currents, IA and ICa2+-K+, across the soma membrane of the Hermissenda Type B photoreceptor, have been shown to remain reduced during retention of classically conditioned behavior. IA and ICa2+-K+ undergo prolonged reduction due to [Ca2+]i elevation produced by a single pairing of a light step with a command depolarization or by iontophoretic injection of Ca2+. One pathway which could contribute to the conversion of transient Ca2+-mediated reduction of K+ currents to the persistent reduction observed with conditioning is that involving C-kinase. To examine the role of C-kinase in the long-term regulation of K+ currents, isolated Type B somata were exposed to at least 25-30 minutes' incubation in artificial sea water (ASW) containing the C-kinase activators 1-oleoyl-2-acetyl-glycerol (OAG) or 12-deoxyphorbol 13-isobutyrate 20-acetate (DPBA) or control substances [e.g., distearyolglycerol (DiSG)]. After exposure to activator (but not to control solutions) and voltage-clamp conditions which caused elevation of cytosolic Ca2+, reductions of IA and ICa2+-K+ were observed which did not reverse (up to 3 hr), even after the activator was removed. Without conditions which induced elevation of cytosolic calcium prolonged incubation with the C-kinase activators had no effect on the membrane currents. Similar exposure of homogenates of the Hermissenda nervous system to OAG and Ca2+ caused enhanced phosphorylation of specific proteins, indicating the presence of C-kinase in the Hermissenda nervous system.

Animals↗
PubMed1986

The effect of vitamin D on bone in vivo.

The linear rate of bone mineral apposition (BMAR) was measured in vitamin D-deficient and vitamin D-sufficient adult rats before and during treatment with either 25-hydroxyvitamin D3 (25OHD3), 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], or 24,25-dihydroxyvitamin D3 [24,25-(OH)2D3]. Dietary vitamin D restriction caused a fall in BMAR which began after 1 week and fell progressively to a value of 35-50% of control values by 4 weeks. The fall in BMAR was related to a fall in the serum concentrations of 25(OH)D3 and 24,25-(OH)2D3, without a fall in the 1,25-(OH)2D3 concentration. Dietary supplementation of the D-deficient animals with either 25OHD3 or 24,25-(OH)2D3 at doses of 200 ng/day restored BMAR. If vitamin D-deficient animals were thyroparathyroid-ectomized before supplementation with vitamin D metabolites, 24,25-(OH)2D3 administration was without effect on BMAR. The combined administration of PTH and 24,25-(OH)2D3 to such animals led to a restoration of the BMAR to normal. In vitamin D-sufficient animals, parathyroidectomy led to a 50% reduction in BMAR, which could be restored by treatment with PTH alone but not with 24,25-(OH)2D3. Simultaneous treatment of these animals with PTH and 24,25-(OH)2D3 led to a greater than normal increase in BMAR (130% of control) in these animals. These data support the concept that 24,25-(OH)2D3 has a role in the regulation of bone formation and/or mineralization, and demonstrate the interrelation between the effects of PTH and 24,25-(OH)2D3 on bone.

24,25-Dihydroxyvitamin D 3↗
PubMed1985

Mechanism of inhibitory action of TMB-8 [8-(NN-diethylamino)octyl-3,4,5-trimethoxybenzoate] on aldosterone secretion in adrenal glomerulosa cells.

The mechanism of 8-(NN-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) action was evaluated in isolated adrenal glomerulosa cells. TMB-8 inhibits both angiotensin II- and K+-stimulated aldosterone secretion in a dose-dependent manner. The ID50 for angiotensin II- and K+-stimulated aldosterone secretion is 46 and 28 microM, respectively. In spite of the fact that 100 microM-TMB-8 inhibits angiotensin II-stimulated aldosterone secretion almost completely, TMB-8 (100 microM) does not inhibit angiotensin II-induced 45Ca2+ efflux from prelabelled cells nor does it affect inositol 1,4,5-trisphosphate-induced calcium release from non-mitochondrial pool(s) in saponin-permeabilized cells. TMB-8 has no inhibitory effect on A23187-induced aldosterone secretion, but 12-O-tetradecanoylphorbol 13-acetate-induced aldosterone secretion is completely abolished. TMB-8 effectively inhibits both angiotensin II- and K+-induced increases in calcium influx but has no effect on A23187-induced calcium influx. TMB-8 inhibits the activity of protein kinase C dose-dependently. These results indicate that TMB-8 inhibits aldosterone secretion without inhibiting mobilization of calcium from an intracellular pool. The inhibitory effect of TMB-8 is due largely to an inhibition of plasma membrane calcium influx, but this drug also inhibits the activity of protein kinase C directly.

Adrenal Glands↗
PubMed1985

A transient rise in intracellular free calcium is not a sufficient stimulus for respiratory burst activation in human polymorphonuclear leukocytes.

Binding of murine monoclonal antibody PMN7C3 to human neutrophils results in a large rapid, dose dependent transient increase in intracellular free calcium as measured by QUIN-2 fluorescence. Unlike other calcium mobilizing agents PMN7C3 does not induce any increase in respiratory burst activity over basal level. The PMN7C3 effect requires multivalent binding. Chelation of extracellular calcium does not significantly decrease the fluorescence transient generated by exposure to PMN7C3. Lowering of basal levels of intracellular free calcium concentration by maintaining QUIN-2-loaded PMN in calcium free medium eliminates the fluorescence transient. The observations demonstrate that a cell surface receptor mediated intracellular free calcium transient may be generated without any associated respiratory burst activation.

Antibodies, Monoclonal↗