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Biomedical subjects

H Rasmussen

Publications and source records attributed to H Rasmussen.

At least 163 records · Page 9Linked to original sources
PubMed1985

Characteristics of angiotensin II-, K+- and ACTH-induced calcium influx in adrenal glomerulosa cells. Evidence that angiotensin II, K+, and ACTH may open a common calcium channel.

The characteristics of angiotensin II-, K+-, and adrenocorticotropin (ACTH)-induced calcium influx were studied in isolated adrenal glomerulosa cells. Basal calcium influx rate is 0.64 +/- 0.09 nmol/min/mg of protein. Addition of angiotensin II (1 nM) causes a rapid 230% increase in calcium influx rate. This angiotensin II-induced calcium influx is sustained and is rapidly reversed by angiotensin II antagonist, [Sar1,Ala8]angiotensin II. Addition of either K+ or ACTH (1 nM) causes a 340 or 160% increase, respectively, in the rate of calcium influx. The effect of either angiotensin II, K+, or ACTH on calcium influx is dependent on extracellular calcium. The apparent Km for calcium is 0.46, 0.35, and 0.32 mM, respectively. When the extracellular concentration of K+ is 2 mM, neither angiotensin II nor ACTH stimulates calcium influx. Conversely, when extracellular K+ is increased to 6 mM, both angiotensin II and ACTH cause a greater stimulation of calcium influx than at 4 mM K+. When extracellular K+ is increased to 10 mM, calcium influx is 360% of the basal influx seen at 4 mM K+, and neither angiotensin II nor ACTH further stimulates the influx rate. Nitrendipine (1 microM) blocks both angiotensin II- and K+-induced calcium influx completely. In contrast, 10 microM nitrendipine does not completely block ACTH-induced calcium influx. The calcium channel agonist, BAY K 8644, also stimulates calcium influx; 10 nM BAY K 8644 leads to a rate of calcium influx which is 185% of basal. This BAY K 8644-induced increase in calcium influx and that caused by either angiotensin II or ACTH are additive. In contrast, BAY K 8644 has more than an additive effect on the calcium influx when paired with 6 mM K+. These results suggest that angiotensin II, K+, and ACTH stimulate calcium influx via a common calcium channel but act by different mechanisms to alter its function.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1985

Role of calcium fluxes in the sustained phase of angiotensin II-mediated aldosterone secretion from adrenal glomerulosa cells.

When angiotensin II stimulates aldosterone secretion, it causes a rapid but transient mobilization of calcium from an intracellular pool and a sustained increase in the influx of calcium in adrenal glomerulosa cells. The present studies were undertaken to determine the respective roles of the two angiotensin II-induced changes in cellular calcium metabolism in modulating events during the sustained phase of cellular response which is thought to be mediated by the C-kinase branch of the calcium messenger system. The sustained response to angiotensin II is only 50% of maximal in cells pretreated with dantrolene in a concentration sufficient to inhibit the angiotensin II-induced mobilization of intracellular calcium. Also, if A23187 is added to cells simultaneously with 1-oleoyl-2-acetylglycerol (OAG), the aldosterone secretory response is similar to that seen after angiotensin II. However, if A23187 is added first and the transient aldosterone secretory response allowed to decay, and OAG then added, the sustained aldosterone secretory response is only 45-50% of maximal. Addition of the calcium channel agonist, BAY K 8644, with OAG leads to an aldosterone secretory response which is only 50% of maximal, but if upon addition of OAG and BAY K 8644 the cells are also exposed for 5 min to media containing 8 mM K+, then the sustained secretory response is maximal. These data imply that the initial transient rise in the [Ca2+] of the cell cytosol plays a role in determining the extent to which C-kinase is shifted from its calcium-insensitive to its calcium-sensitive form. The second group of experiments examined the relationship between the sustained angiotensin II-induced increase in plasma membrane calcium influx and the sustained aldosterone secretory response. The results show that in the presence of 1 microM nitrendipine or 2 mM extracellular K+, angiotensin II causes no increase in calcium influx and only a transient rather than a sustained increase in the rate of aldosterone secretion indicating that the sustained phase of the response is dependent upon a continued high rate of Ca2+ influx which regulates the rate of turnover of the activated C-kinase.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1985

Intracellular calcium and adenosine 3',5'-cyclic monophosphate as mediators of potassium-induced aldosterone secretion.

We compared the action of K+ on aldosterone secretion from isolated bovine adrenal glomerulosa cells with that of ionophore A23187. Addition of either 50 nM-A23187 or 8 mM-K+ to perifused cells induces a similar initial aldosterone-secretory responses, and a similar sustained increases in Ca2+ entry. However, K+-induced secretion is more sustained than is A23187-induced secretion, even though each agonist appears to act by increasing Ca2+ entry into the cells. When [3H]inositol-labelled cells are stimulated by 8 mM-K+, a small decrease in phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] is observed. This decrease is not accompanied by an increase in inositol trisphosphate (InsP3) concentration. Also, if [3H]arachidonic acid-labelled cells are exposed to 8 mM-K+, there is no increase in [3H]diacylglycerol production. When [3H]inositol-labelled cells are stimulated by 50 nM-A23187, a small decrease in PtdIns(4,5)P2 is observed. This decrease is not accompanied by an increase in InsP3. The cyclic AMP content of K+-treated cells was approximately twice that in A23187-treated cells. If cells are perifused simultaneously with 50 nM-forskolin and 50 nM-A23187, the initial aldosterone-secretory response is similar to that induced by A23187 alone, and the response is sustained rather than transient, and is similar to that seen during perifusion of cells with 8 mM-K+. This dose of forskolin (50 nM) causes an elevation of cyclic AMP concentration in A23187-treated cells, to a value similar to that in K+-treated cells. These results indicate that, in K+-treated cells, a rise in cyclic AMP content serves as a positive sensitivity modulator of the Ca2+ message, and plays a key role in mediating the sustained aldosterone-secretory response.

Adrenal Glands↗
PubMed1985

Protein kinase C activity in renal microvillus membranes.

Protein kinase C activity was found in rabbit renal microvillus membrane vesicles. C-kinase activity was assayed by examining H1 histone phosphorylation using microvillus membrane vesicles dispersed with Triton X. Calcium-activated protein kinase activity was only demonstrable in the presence of phosphatidylserine (PS). With PS (15 micrograms/ml) the Ka for activation by calcium was 1.04 microM. This was reduced to 0.38 microM by addition of diolein (3.75 micrograms/ml). These activations were dose-dependent and their combined synergistic activation could be reproduced by the combination of PS (15 micrograms/ml) and the phorbol ester, TPA (1.17 ng/ml). During microvillus membrane purification, protein kinase C activity enriched 5-fold relative to its activity in the homogenates. The activity was not due to trapped cytosol or adventitious association with microvillus membranes during homogenization. During further purification on sucrose gradients, the C-kinase activity coenriched with brush border and not with basolateral enzyme markers. We conclude that protein kinase C is a normal component of the renal microvillus membrane.

Animals↗
PubMed1985

Role of calcium and cAMP in the action of adrenocorticotropin on aldosterone secretion.

When the dose-response curve of adrenocorticotropin (ACTH)-induced aldosterone secretion is compared to that of ACTH-induced intracellular cAMP, the ED50 for intracellular cAMP is more than 10 times as high as that for aldosterone production. In contrast, the dose-response curve of forskolin-induced aldosterone secretion correlates well with that for forskolin-induced intracellular cAMP. ACTH, but not forskolin, increases calcium influx into glomerulosa cells without inducing the mobilization of calcium from an intracellular pool. The effect of ACTH on calcium influx is dose-dependent and ED50 is 3.5 X 10(-11) M. In a perifusion system, the effect of 1 nM ACTH on aldosterone secretion is much greater than that of 1 microM forskolin, even though these two stimulators induce identical increases in the intracellular cAMP. Perifusion with combined A23187 (50 nM) and forskolin (1 microM) stimulates aldosterone secretion to a value comparable to that induced by 1 nM ACTH. Likewise, BAY K 8644 (1 nM), which induces a comparable increase in calcium influx, potentiates the effect of 1 microM forskolin. When the intracellular [Ca2+] is fixed at either 100 or 300 nM, forskolin-stimulated intracellular cAMP content is identical, but ACTH-stimulated intracellular cAMP content at 100 nM [Ca2+]i is 60% of that at 300 nM [Ca2+]i. Both the ACTH- and forskolin-induced aldosterone secretion rate is higher at 300 nM than at 100 nM [Ca2+]i. These results indicate that ACTH stimulates calcium influx, that calcium potentiates ACTH-induced but not forskolin-induced cAMP generation, and that Ca2+ and cAMP act as synarchic messengers in ACTH-mediated aldosterone secretion.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1985

Activation of tracheal smooth muscle contraction: synergism between Ca2+ and activators of protein kinase C.

The effects of divalent ionophores (A23187 and ionomycin), Ca2+ channel agonist (BAY K 8644), and protein kinase C (C-kinase) activators [phorbol 12-myristate 13-acetate (PMA), mezerein] on bovine tracheal smooth muscle contraction were investigated. A23187 (5 microM) and ionomycin (0.5 microM) produced a prompt but transient contraction. C-kinase activators either produced no effect--e.g., PMA at 200 nM--or produced a rise in tension that was slow in onset but then gradually increased--e.g., mezerein at 400 nM. In contrast, ionophores and C-kinase activators, in combination, acted synergistically to produce a prompt and sustained contractile response that is reminiscent of that observed in response to carbachol, a cholinergic agonist. In addition, BAY K 8644 (20 nM), which has a minimal effect on tension by itself, could significantly enhance contraction induced by C-kinase activators. The contraction induced by all of these agents was quickly reversed either by removal of extracellular Ca2+ or upon addition of forskolin, an activator of adenylate cyclase. A similar reversal of carbachol-induced contraction by forskolin was observed with carbachol-induced contraction. These findings strongly suggest that C-kinase plays an important role in mediating tracheal smooth muscle contraction.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1985

Effects of ANG II and K+ on Ca efflux and aldosterone production in adrenal glomerulosa cells.

A comparison was made of the effects of angiotensin II (ANG II) and K+ on aldosterone secretion and calcium efflux from porcine adrenal glomerulosa cells. In the presence of 1.25 mM Ca2+ in the perifusion medium, both 1 x 10(-9) M ANG II and 12 mM K+ caused a 3-fold increase in rate of aldosterone secretion. ANG II caused a 3.5-fold increase in the fractional efflux ratios of radiocalcium from cells prelabeled with 45Ca, but K+ caused only a 1.5-fold increase. When the perifusate contained no Ca2+ or the Ca2+ was replaced by 0.6 mM Sr2+, the effects of K+ on both 45Ca efflux and aldosterone production were abolished. On the other hand, ANG II still caused approximately the same increase in the fractional efflux ratio of radiocalcium and 25-50% of the normal increase in aldosterone production rate. When the perifusate contained 1.25 mM calcium and 25 microM dantrolene, K+ produced the same 1.5-fold increase in calcium efflux and the same maximal rate of aldosterone production as seen in the absence of dantrolene. In contrast, dantrolene greatly inhibited ANG II-induced increase in the fractional efflux ratio of calcium, 1.5-fold compared with 3.5-fold in the absence of dantrolene. Likewise, dantrolene delayed the onset of the ANG II-induced increase in aldosterone secretion and reduced the maximal rate of secretion to 50%. Cells incubated with both dantrolene and media containing no Ca2+ or containing Sr2+ in place of Ca2+ showed no response to ANG II either in terms of calcium efflux or aldosterone production.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗
PubMed1985

Possible role of phospholipase A2 action and arachidonic acid metabolism in angiotensin II-mediated aldosterone secretion.

When [3H]arachidonic acid-labeled calf adrenal glomerulosa cells are stimulated by angiotensin II (AII), free [3H]arachidonic acid is released. AII treatment significantly decreases radioactivity in phosphatidylinositol but not in other phospholipids. Inhibitors of phospholipase A2 (PL-A2) activity, quinacrine and p-bromophenacyl bromide, inhibit AII-stimulated aldosterone secretion from glomerulosa cells in a dose-dependent manner. The effect of these inhibitors is irreversible when used at high concentration, but not when employed at lower concentration. Exogenous PL-A2 as well as arachidonic acid stimulates both radiocalcium efflux and aldosterone secretion. Unlike AII, stimulation of aldosterone secretion by PL-A2 is only transient. Radiocalcium efflux induced by PL-A2 is greater than that induced by AII and is not inhibited by either nitrendipine or dantrolene. Pretreatment with PL-A2 abolishes the radiocalcium efflux response to subsequent AII, whereas AII pretreatment does not abolish the subsequent PL-A2-mediated radiocalcium efflux response. The aldosterone secretory response to AII is not affected by 0.3 microM indomethacin but is inhibited by either of three compounds which inhibit lipoxygenase activity; 5,8,11,14-eicosatetraynoic acid, BW755c, or caffeic acid. In a static incubation system, AII-stimulated aldosterone secretion is inhibited 40-50% by any of these lipoxygenase inhibitors. In a perifusion system, BW755c partially inhibits only the sustained phase of AII-stimulated aldosterone secretion. However, BW755c has no effect on the secretion of aldosterone in response to combined A23187 plus 12-O-tetradecanoyl-phorbol-13-acetate. These results suggest that PL-A2 action is not obligatory in AII-induced aldosterone secretion and that lipoxygenase, but not cyclooxygenase, products of arachidonic acid metabolism may play a role in AII action as positive feed forward mediators.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1985

Plasma membrane calcium flux, protein kinase C activation and smooth muscle contraction.

Isolated perfused rabbit ear arteries contract when treated with 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of the calcium-activated, phospholipid-dependent protein kinase or C-kinase. Under conditions where the calcium concentration in the perfusate is 1.5 mM and the potassium concentration is 4.8 mM, there is a latent period of 70 +/- 19 min (mean +/- S.E.M., n = 10) between TPA addition and the onset of the contractile response. Once initiated, the contractile response is progressive and sustained. When perfusion conditions are altered in such a way as to modify calcium flux across the plasma membrane (i.e., raising the extracellular calcium concentration to 2.5 mM Ca++, raising the extracellular potassium concentration to 10 mM, and/or preincubating the tissues in media containing 100 nM Bay K 8644, a potent calcium channel agonist), the latency period between TPA addition and initiation of the contractile response is significantly reduced (2.5 mM Ca++, 37 +/- 7 min; 10 mM K+ and 2.5 mM Ca++, 11 +/- 3 min; 100 nM Bay K 8644 and 1.5 mM Ca++, 20 +/- 7 min; 100 nM Bay K 8644 and 2.5 mM Ca2+, 8.5 +/- 1.7 min; 10 mM K+ and 100 nM Bay K 8644, 11 +/- 5 min). Likewise, the combination of 2.5 mM calcium, 100 nM Bay K 8644, and 3.3 microM ouabain results in a contractile response 4.5 +/- 2.0 min after TPA addition (means +/- S.E.M., n = 4). Control tissues (absence of TPA addition) run simultaneously show no contractile responses to the various Ca++ flux regulators even after 90 min of incubation.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1984

The temporal integration of the aldosterone secretory response to angiotensin occurs via two intracellular pathways.

Angiotensin II (AII) regulates the secretion of aldosterone from adrenal glomerulosa cells by a calcium-dependent mechanism which involves both the uptake of calcium from the extracellular pool, and the release of calcium from a dantrolene-sensitive intracellular pool. In the present study, it was shown that AII induces the rapid (10 s) hydrolysis of phosphatidylinositol 4-phosphate and -4,5-bisphosphate, leading to the sustained production of inositol bis- and trisphosphate (Ins-P3), and diacylglycerol rich in arachidonic acid. Saponin-permeabilized glomerulosa cells accumulate calcium into a nonmitochondrial pool by an ATP-dependent manner. Ins-P3 (0.5-5 microM) induces a release of Ca2+ from this pool. This release was blocked by dantrolene (10 microM). Adrenal glomerulosa cells were shown to contain the calcium-activated, phospholipid-dependent protein kinase (C-kinase). Perfusion of glomerulosa cells with combined 12-O-tetradecanoyl phorbol 13-acetate and A23187 induced an immediately developing, sustained, maximal secretory response similar to that induced by AII. These data are interpreted in terms of a model in which, after AII addition, there is a flow of information through two separate branches of the calcium messenger system, each with its unique temporal role: a calmodulin branch activated by the transient rise in the [Ca2+] in the cell cytosol, which is largely responsible for the initial transient cellular response; and a C-kinase branch activated by the increase in both cytosolic [Ca2+] and the diacylglycerol content of the plasma membrane, which is largely responsible for the sustained phase of the cellular response. The temporal integration of these two phases underlies the observed pattern of cellular response.

Adrenal Cortex↗
PubMed1984

The role of fatty acids in the regulation of brush-border Ca2+ transport.

The role of the fatty-acid composition of the intestinal brush-border membrane in the control of transmembrane Ca2+ transport was examined by in vitro acylation of endogenous phospholipids. The initial rate of Ca2+ uptake into brush-border membrane vesicles was stimulated 1.6-fold by incubation with 50 microM linoleoyl CoA, which was the most effective CoA ester examined. Oleoyl CoA was also active, but stearoyl CoA, palmitoyl CoA and arachidonyl CoA displayed no activity. The effect of linoleoyl CoA was specific for Ca2+ transport; sodium-dependent phosphate uptake was slightly inhibited and the activity of alkaline phosphatase, a brush-border enzyme, was unaffected. Incubation of brush-border vesicles with either stimulatory (oleate) or nonstimulatory (stearate) CoA esters resulted in the incorporation of fatty acid into the four major phospholipid classes, suggesting a fatty-acid specificity of the Ca2+ transport phenomenon. These results are consistent with the hypothesis that fatty acids are important elements in the control of brush-border Ca2+ transport.

Acyl Coenzyme A↗
PubMed1984

Synergistic stimulation of prolactin release by phorbol ester, A23187 and forskolin.

The effects of 12-0-tetradecanoyl-phorbol-13-acetate (TPA), A23187, forskolin and thyrotropin-releasing hormone (TRH) on prolactin release from GH4C1 cells were compared. TPA caused a 2-fold release, maximum after 6 or more min, that was sustained for 30 min or more. A23187 caused only a small and variable response that peaked within 4 to 6 min. Combination of TPA and A23187 caused a rapid 3- to 5-fold increase in release that declined slowly. TRH increased prolactin release 3- to 5-fold, reaching a maximum within 4 min, followed by sustained release at lower rates. Forskolin had little effect by itself, but potentiated release caused either by combined TPA and A23187, or by TRH. These data are consistent with a model in which two branches of the Ca2+ messenger system participate in the action of TRH, a calmodulin branch and a C-kinase branch that interact to cause large amounts of sustained release. Forskolin, by regulating the cyclic AMP content of the cell determines the set point around which the Ca2+ messenger system operates.

Animals↗