Unique calcium dependencies of the activating mechanism of the early and late aldosterone biosynthetic pathways in the rat

1986 ◽  
Vol 110 (2) ◽  
pp. 315-325 ◽  
Author(s):  
R. J. Schiebinger ◽  
L. M. Braley ◽  
A. Menachery ◽  
G. H. Williams
Keyword(s):  
Angiotensin Ii ◽  
Calcium Channel ◽  
Biosynthetic Pathway ◽  
Calcium Influx ◽  
Extracellular Calcium ◽  
Aldosterone Secretion ◽  
Calcium Dependency ◽  
Pathway Activation ◽  
Dihydropyridine Calcium Channel Antagonist ◽  
Channel Dependent

ABSTRACT This study compared the extracellular calcium dependency and the enzymatic locus of that dependency for N6,O2′-dibutyryl cyclic AMP (dbcAMP)-, angiotensin II- and potassium-stimulated aldosterone secretion in dispersed rat glomerulosa cells. The need for extracellular calcium, calcium influx, and specifically for calcium influx through the calcium channel was examined. dbcAMP, angiotensin II and potassium, in the presence of calcium (3·5 mmol/l), significantly (P < 0·01) increased aldosterone output by at least 1·5-fold. Yet in the absence of extracellular calcium or in the presence of lanthanum (an inhibitor of calcium influx by most mechanisms) all three stimuli failed to increase aldosterone secretion. Nifedipine, a dihydropyridine calcium channel antagonist, significantly (P < 0·01) reduced angiotensin II- and potassium-stimulated aldosterone secretion, but had no effect on dbcAMP-stimulated aldosterone secretion (100 ± 14 vs 105 ± 19 pmol/106 cells). Likewise nitrendipine failed to inhibit ACTH-stimulated aldosterone secretion. Angiotension II and potassium activation of both the early aldosterone biosynthetic pathway (as reflected by pregnenolone production in the presence of cyanoketone) and also its late pathway (as reflected by the conversion of exogenous corticosterone to aldosterone in the presence of cyanoketone) were significantly (P < 0·01) inhibited by lanthanum, nifedipine and by reducing the extracellular calcium concentration. However, with dbcAMP stimulation, none of these manipulations modified pregnenolone production. Late pathway activation by dbcAMP was inhibited by lanthanum and a reduction in extracellular calcium, but not by nifedipine. These observations suggest that: (1) the extracellular calcium dependency of dbcAMP-, angiotensin II- and potassium-stimulated aldosterone secretion reflects a need for calcium influx; (2) with dbcAMP stimulation, activation of the late pathway is dependent on calcium influx by a calcium channel-independent mechanism, whereas activation of the early pathway is not dependent on extracellular calcium or calcium influx and (3) activation of both the early and late pathway by angiotensin II and potassium is dependent on calcium influx by a calcium channel-dependent mechanism. Therefore, we conclude that the mechanism of activation of the early aldosterone biosynthetic pathway by dbcAMP is different from angiotensin II or potassium and early pathway activation is distinct from that of late pathway activation with dbcAMP stimulation. J. Endocr. (1986) 110, 315–325

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

1985 ◽  
Vol 232 (1) ◽  
pp. 87-92 ◽  
Author(s):  
I Kojima ◽  
K Kojima ◽  
H Rasmussen
Keyword(s):  
Protein Kinase C ◽  
Angiotensin Ii ◽  
Protein Kinase ◽  
Calcium Release ◽  
Calcium Influx ◽  
Inhibitory Effect ◽  
Dependent Manner ◽  
Aldosterone Secretion ◽  
Kinase C ◽  
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.

Effect of osmolality on cytosolic free calcium and aldosterone secretion

1992 ◽  
Vol 262 (1) ◽  
pp. E68-E75 ◽  
Author(s):  
W. Wang ◽  
N. Hayama ◽  
T. V. Robinson ◽  
R. E. Kramer ◽  
E. G. Schneider
Keyword(s):  
Calcium Influx ◽  
Potassium Concentration ◽  
Sodium Concentration ◽  
Cytosolic Calcium ◽  
Extracellular Calcium ◽  
Free Calcium ◽  
Aldosterone Secretion ◽  
Voltage Dependent ◽  
Glomerulosa Cells ◽  
Dose Dependent

Alterations in extracellular osmolality have powerful inverse effects on basal and potassium- and angiotensin-stimulated aldosterone secretion. With the use of bovine glomerulosa cells grown in primary culture, the effects of alterations in osmolality on cytosolic calcium concentration ([Ca2+]c), efflux and uptake of 45Ca2+, and aldosterone secretion were determined. Alterations in osmolality, independent of sodium concentration, have inverse effects on aldosterone secretion, which are correlated with simultaneous changes in [Ca2+]c measured using fura-2. Reductions in osmolality cause dose-dependent biphasic increases in [Ca2+]c different from the monophasic increases in [Ca2+]c produced by increases in potassium concentration. Like potassium- and angiotensin-stimulated increases in [Ca2+]c, hypotonically induced increases in [Ca2+]c are associated with an increase in 45Ca2+ efflux. Reductions in osmolality also increased the uptake of 45Ca2+, an effect apparent at 2 min and persistent for at least 30 min. In the absence of extracellular calcium, reductions in osmolality, as increases in potassium concentration but not angiotensin, fail to increase [Ca2+]c, efflux of 45Ca2+, or aldosterone secretion. In conclusion, osmolality-induced alterations in aldosterone secretion are associated with parallel changes in [Ca2+]c, effects caused by alteration in the influx of extracellular calcium. On the basis of these and previous studies, we hypothesize that osmolality affects calcium influx by activating voltage-dependent or stretch-activated calcium channels.

Modulation of Ca2+ channels by atrial natriuretic peptide in the bovine adrenal glomerulosa cell

1991 ◽  
Vol 69 (10) ◽  
pp. 1553-1560 ◽  
Author(s):  
P. Q. Barrett ◽  
C. M. Isales ◽  
W. B. Bollag ◽  
R. T. McCarthy
Keyword(s):  
Patch Clamp ◽  
Calcium Channels ◽  
Atrial Natriuretic Peptide ◽  
Calcium Channel ◽  
Natriuretic Peptide ◽  
Calcium Influx ◽  
Secretory Response ◽  
Aldosterone Secretion ◽  
Channel Current ◽  
Atrial Natriuretic

In the bovine adrenal glomerulosa cell, calcium influx through voltage-dependent calcium channels is critical to maintaining an aldosterone secretory response. In patch clamp, atrial natriuretic peptide (ANP) inhibits T-type calcium channel current yet stimulates L-type calcium channel current. In the present study the channel effects of ANP observed in the patch-clamp configuration were extended and related to populations of cells. We observed the following. (i) The effect of ANP on T-channel current resulted in the reduction in the open state probability. ANP decreased the mean open state duration from 14.2 to 1.8 ms/sweep. (ii) In the weakly depolarized cell stimulated by 8 mM K+, ANP reduced the level of aequorin luminescence (a measure of cytosolic calcium) and completely inhibited the stimulated rate of aldosterone secretion, returning it to prestimulation values. These effects are consistent with a decrease in net calcium channel influx and the reported inhibition of T-channel current. In contrast, the calcium channel blocker, nitrendipine, which at low dose selectively blocks L-type calcium channel flux, only slightly reduced luminescence, and partially inhibited the sustained secretory response. (iii) In the strongly depolarized cell, stimulated by 60 mM K+, ANP increased the level of aequorin luminescence consistent with an increase in net calcium channel influx and the reported stimulation of L-channel current. These results indicate that under physiological conditions the inhibition of T-type calcium channels may be involved in the inhibition of the aldosterone secretion induced by ANP.Key words: ANP, aldosterone secretion, calcium channels, intracellular calcium, adrenal glomerulosa.

Inhibition by calcium channel blockers of the glycogenolytic effect of glucagon in perfused rat liver

1982 ◽  
Vol 99 (4) ◽  
pp. 559-566 ◽  
Author(s):  
Satoshi Kimura ◽  
Toshio Matsumoto ◽  
Ryoko Tada ◽  
Etsuro Ogata ◽  
Kaoru Abe
Keyword(s):  
Cyclic Amp ◽  
Calcium Channel ◽  
Rat Liver ◽  
Calcium Channel Blockers ◽  
Calcium Influx ◽  
Extracellular Calcium ◽  
Channel Blockers ◽  
Perfused Rat Liver ◽  
Glycogenolytic Effect ◽  
Glucose Output

Abstract. Verapamil and diltiazem, calcium channel blockers, inhibited significantly the glucagon-induced glucose output and 45Ca efflux from perfused rat liver at concentrations higher than 50 μm when the perfusate contained calcium. Although the blockers partially interfered with glucagon-induced elevation of cyclic AMP in the tissue, they also inhibited the effects of cyclic AMP. The blockers did not show the inhibitory effects in the absence of perfusate calcium. However, the inhibition of calcium influx into hepatocytes by omission of extracellular calcium or addition of EGTA did not interfere with these effects of glucagon and cyclic AMP. In the presence of extracellular calcium, the blockers did not inhibit cyanide-induced glucose output, indicating that the activity of glycogen phosphorylase and later processes leading to glucose output were not affected by the blockers. These data suggest that, in the presence of calcium, the blockers inhibit the effect of glucagon also at a step (or steps) subsequent to cyclic AMP production and before the activation of phosphorylase b, probably by inhibiting glucagon-induced mobilization of calcium from intracellular calcium pools rather than inhibiting calcium influx into hepatocytes.

Possible inhibition of canine ventricular sarcoplasmic reticulum by BAY K 8644

1989 ◽  
Vol 257 (2) ◽  
pp. H407-H414 ◽  
Author(s):  
L. V. Hryshko ◽  
T. Kobayashi ◽  
D. Bose
Keyword(s):  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Calcium Channel ◽  
Calcium Influx ◽  
Scattered Light ◽  
Negative Relationship ◽  
Extracellular Calcium ◽  
Bay K 8644 ◽  
Racemic Mixture ◽  
Channel Agonist

The calcium-channel agonist-antagonist racemic mixture of BAY K 8644 as well as the pure calcium-channel agonist enantiomer, converted rest potentiation in canine ventricular muscle to rest depression. The depressed postrest beats had increased action potential plateau heights and durations, suggesting that extracellular calcium entry was enhanced. BAY K 8644 did not alter the time to peak tension of either steady-state or postrest beats. Although BAY K 8644 slightly increased the amplitude of rapid-cooling contractures (RCC) immediately after an electrically evoked steady-state contraction (RCCss), the RCC amplitude rapidly decreased with increasing durations of rest. These results suggest that increased calcium influx because of BAY K 8644 increases the pool of releasable calcium during steady-state stimulation. However, they also indicate that BAY K 8644 causes acceleration of diastolic loss of calcium from the sarcoplasmic reticulum (SR). Scattered light intensity fluctuation measurements showed that the negative inotropic effect of BAY K 8644 on postrest contraction was not caused by calcium overloading of the SR, since BAY K 8644 reduced asynchronous myofilament motion. A negative relationship found between extracellular calcium and BAY K 8644-induced postrest depression also rules out the possibility that the latter effect is caused by intracellular calcium overload. BAY K 8644 seems to accelerate the loss of calcium from the SR during diastole by a pathway that does not appear to pass through the myofilaments.

Absence of blocking effects on cardiac slow calcium channels by the intracellular calcium antagonist 2-n-propyl-3-dimethylamino-5,6-methylenedioxyindene

1982 ◽  
Vol 60 (6) ◽  
pp. 841-849 ◽  
Author(s):  
Joseph J. Lynch ◽  
Ralf G. Rahwan
Keyword(s):  
Calcium Antagonist ◽  
Calcium Channels ◽  
Calcium Channel ◽  
Calcium Influx ◽  
Negative Inotropic Effect ◽  
Calcium Entry ◽  
Extracellular Calcium ◽  
Myocardial Cells ◽  
Inotropic Effects ◽  
Site Of Action

Extensive pharmacological evidence supports the contention that 2-n-propyl-3-dimcthylamino-5,6-methylenedioxyindene hydrochloride (pr-MDI) is a calcium antagonist with a predominantly intracellular site of action. On the other hand, electrophysiological evidence points to a possible membrane slow inward calcium channel blocking property of this agent. To gain further insight as to the site of action of pr-MDI, the interactions between the negative inotropic action of this agent and the positive inotropic actions of excess extracellular calcium (which directly penetrates the myocardial cells through the slow calcium channels), isoproterenol (which indirectly augments calcium influx through the slow calcium channels), and ouabain (which enhances calcium influx through membrane calcium entry routes distinct from the slow calcium channels) were investigated in the isolated, electrically driven guinea pig left atrium. Although excess extracellular calcium, isoproterenol, and ouabain reversed the negative inotropic effect of pr-MDI, an analysis of the concentration–response relationships to all three positive inotropic agents in the presence and the absence of pr-MDI demonstrated that this agent did not significantly inhibit the contractile effects of calcium, isoproterenol, or ouabain, at pr-MDI concentrations which exhibit intrinsic negative inotropic effects. It is concluded that pr-MDI does not block the membrane slow inward calcium channel nor other presumptive membrane routes of calcium entry into myocardial cells at concentrations of 10−4 M or less. At very high concentrations (T × 10−4 M) some inhibition of slow channel calcium influx may occur.

Spike aftercurrents in R15 of Aplysia: their relationship to slow inward current and calcium influx

1984 ◽  
Vol 51 (2) ◽  
pp. 387-403 ◽  
Author(s):  
D. V. Lewis
Keyword(s):  
Calcium Channel ◽  
Intracellular Calcium ◽  
Calcium Channel Blockers ◽  
Calcium Influx ◽  
Extracellular Calcium ◽  
Slow Inward Current ◽  
Extracellular Potassium ◽  
Channel Blockers ◽  
Tetraacetic Acid ◽  
Inward Current

Spikes in the bursting neuron, R15, are followed by depolarizing afterpotentials (35) and often by delayed hyperpolarizing afterpotentials as well. Placing the cell in a voltage clamp after a spike allows measurement of the depolarizing aftercurrent (DAC) and hyperpolarizing aftercurrent (HAC) that underlie the afterpotentials. Subthreshold depolarizations give rise to small DACs and HACs. The DAC and the slow inward current (SIC) of R15 are reduced or blocked in a similar manner by many experimental manipulations, e.g., application of dopamine, zero-calcium seawater, zero-sodium seawater, or calcium-channel blockers (Mn2+ and La3+), or cooling the cell from 21-22 degrees C to 10 degrees C. Neither the DAC nor the SIC were blocked by tetrodotoxin (100 uM) and neither was sensitive to altered extracellular potassium. Both the DAC and SIC become larger as the holding potential of the cell is progressively depolarized from -70 to -40 mV. DACs are sensitive to the injection of intracellular calcium chelators (EGTA (ethylene glycol-bis(beta-aminoethyl ether)-N,N1-tetraacetic acid) or EDTA [ethylenedinitrilo)tetraacetic acid]. DAC amplitude is approximately 90% reduced by intracellular EGTA concentration near 1mM. In contrast, the SIC is unchanged or much less affected by the calcium buffers. DACs are also more sensitive to low (1 mM) extracellular calcium than is the SIC. The HAC is also a calcium-dependent current. It is blocked by any experimental manipulation reducing calcium influx or intracellular calcium accumulation, i.e., reduced extracellular calcium, calcium-channel blockers, or intracellular EGTA. We suggest that the DAC and the SIC are carried by the same conductance mechanism. In the case of the DAC, the conductance might be activated by a rise in intracellular calcium activity accompanying the spike and, in the case of the SIC, depolarization per se may be the most important activating condition.

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