Agonist-induced frequency modulation of Ca2+ oscillations in salt gland secretory cells

1991 ◽  
Vol 261 (1) ◽  
pp. C177-C184 ◽  
Author(s):  
K. M. Crawford ◽  
E. L. Stuenkel ◽  
S. A. Ernst
Keyword(s):  
Intracellular Calcium ◽  
Frequency Modulation ◽  
Calcium Concentration ◽  
Salt Gland ◽  
Effective Concentration ◽  
Secretory Cells ◽  
Oscillatory Frequency ◽  
Fura 2 ◽  
Dose Dependent ◽  
Sustained Increase

Oscillations in intracellular calcium concentration ([Ca2+]i) induced by the acetylcholine analogue carbachol (CCh) were characterized by microspectrofluorimetry of fura-2 in single secretory cells from the avian salt gland. The frequency of oscillations increased in graded fashion with [CCh] between 25 nM (2.7 +/- 0.6 min-1) and 250 nM (11.8 +/- 1.4 min-1), whereas the amplitude of the spikes was independent of [CCh]. An interperiod return to prestimulatory [Ca2+]i was generally seen only at very low (25 nM) CCh. Between 50 and 250 nM CCh, oscillations were associated with sustained elevated [Ca2+]i levels. The amplitude of the oscillatory spikes was found not to exceed that of initial spikes arising from prestimulatory [Ca2+]i, despite the dose-dependent [effective concentration at 50% (EC50) = 200 nM CCh] sustained rise in [Ca2+]i. At 1 microM CCh, oscillations gave way to a maximal sustained increase in [Ca2+]i. Reduction of [Ca2+]o to 1.5 microM during an oscillatory train or blockage of Ca2+ influx with Ni+ resulted in a reduction in sustained Ca2+i levels and in frequency, but not amplitude, of oscillations. A relationship between the sustained partial rise in [Ca2+]i derived from Ca2+ influx and the oscillatory frequency at a given [CCh] was further indicated by the lower frequency (P less than 0.01) of the early spikes in a train when interspike [Ca2+]i initially returned to near-basal levels. In some cells, oscillations were slow enough (less than 2 min-1) to resolve an interperiod of elevated baseline [Ca2+]i, showing that the latter can occur independent of the repetitive Ca2+ spikes. (ABSTRACT TRUNCATED AT 250 WORDS)

Multiple calcium mobilization pathways in single avian salt gland cells

1990 ◽  
Vol 258 (2) ◽  
pp. C289-C298 ◽  
Author(s):  
E. L. Stuenkel ◽  
S. A. Ernst
Keyword(s):  
Salt Gland ◽  
Transient Increase ◽  
Secretory Cells ◽  
Free Medium ◽  
Subsequent Removal ◽  
Intracellular Pool ◽  
Gland Cells ◽  
Agonist Stimulation ◽  
Induced Changes ◽  
Sustained Increase

Agonist-induced changes in intracellular Ca2+ concentration ([Ca2+]i) in individual secretory cells from the avian salt gland were detailed using dual-wavelength microspectrofluorimetry of the Ca2(+)-sensitive fluorescent probe fura-2. Resting [Ca2+]i averaged 42 +/- 5 nM. Stimulation with the cholinergic agonist carbachol (1 microM) resulted in a rapid increase in [Ca2+]i to 308 +/- 26 nM, which was sustained at a nearly constant elevated level (328 +/- 31 nM) throughout agonist application. In the absence of extracellular Ca2+ or in the presence of an inorganic blocker of Ca2+ entry (Ni2+, 1 mM), only a transient increase in [Ca2+]i occurred on agonist stimulation, whereas subsequent readmission of Ca2+ or washout of Ni2+ reinitiated a sustained increase in [Ca2+]i. The initial transient response results from Ca2+ release from intracellular stores, whereas the sustained phase represents entry of extracellular Ca2+ into the cytoplasm. Repetitive stimulations in Ca2(+)-free medium alternating with Ca2(+)-containing medium were performed to examine the mechanisms involved in refilling of the agonist-sensitive intracellular pool. After depletion of the intracellular pool by stimulation in Ca2(+)-free medium, removal of the agonist and readmission of Ca2+ resulted in a rapid transient increase in [Ca2+]i that could be blocked by Ni2+, La3+, or elevated K+. Subsequent removal of extracellular Ca2+ and restimulation nonetheless showed that complete refilling of the intracellular pool had occurred in each case. These results suggest that two separate Ca2(+)-entry mechanisms, one sensitive to Ni2+, La3+, and elevated K+ and responsible for the agonist-induced increase in [Ca2+]i and one insensitive to the blockers and involved in refilling of the intracellular pool, may exist in salt gland cells. Spontaneous oscillations of [Ca2+]i that are independent of extracellular Ca2+ have also been observed in 10% of the cells. The abolition of the oscillations by depletion of the agonist-sensitive pool suggests this pool as the Ca2+ source for the oscillations.

Axotomy induces a transient and localized elevation of the free intracellular calcium concentration to the millimolar range

1995 ◽  
Vol 74 (6) ◽  
pp. 2625-2637 ◽  
Author(s):  
N. E. Ziv ◽  
M. E. Spira
Keyword(s):  
Intracellular Calcium ◽  
Calcium Concentration ◽  
Intracellular Calcium Concentration ◽  
Concentration Gradients ◽  
Fura 2 ◽  
Direct Demonstration ◽  
Free Intracellular Calcium ◽  
Axonal Transection ◽  
Transient Elevation

1. Axonal transection triggers a cascade of pathological processes that frequently lead to the degeneration of the injured neuron. It is generally believed that the degenerative process is triggered by an overwhelming influx of calcium through the cut end of the axon. 2. Theoretical considerations and indirect observations suggest that axotomy is followed by an increase in the free intracellular calcium concentration ([Ca2+]i) to the millimolar level. In contrast, only relatively modest and transient elevation in [Ca2+]i to the micromolar level was revealed by recent fura-2 studies. 3. In the current study we used the low-affinity Ca2+ indicator mag-fura-2 to reexamine the spatiotemporal distribution pattern of Ca2+ after axotomy and to map the free intracellular Mg2+ concentration gradients. 4. We report that axotomy elevates [Ca2+]i well beyond the "physiological" range of calcium concentrations, to levels > 1 mM near the tip of the cut axon and to hundreds of micromolars along the axon further away from the cut end. Nevertheless, [Ca2+]i recovers to the control levels within 2-3 min after the resealing of the cut end. 5. A comparison of the behavior of fura-2 and mag-fura-2 in the cytosol of the axotomized neurons reveals that the determination of [Ca2+]i by fura-2 largely underestimates the actual intracellular Ca2+ concentrations. 6. Experiments in which one branch of a bifurcated axon was transected revealed that the elevation in [Ca2+]i is confined to the transected axonal branch and does not spread beyond the bifurcation point. 7. After axotomy, the intracellular Mg2+ concentration equilibrates rapidly with the external concentration and then recovers at a rate somewhat slower than that of [Ca2+]i. 8. To the best of our knowledge, this study is the first direct demonstration that axotomy elevates [Ca2+]i to the millimolar range and that neurons are able to recover from these extreme calcium concentrations.

Volume regulation and intracellular calcium in the rabbit proximal convoluted tubule

1991 ◽  
Vol 260 (6) ◽  
pp. F861-F867 ◽  
Author(s):  
J. S. Beck ◽  
S. Breton ◽  
R. Laprade ◽  
G. Giebisch
Keyword(s):  
Intracellular Calcium ◽  
Cell Volume ◽  
Sodium Transport ◽  
Calcium Concentration ◽  
Basolateral Membrane ◽  
Potassium Conductance ◽  
Proximal Convoluted Tubule ◽  
Intracellular Calcium Concentration ◽  
Cell Swelling ◽  
Sustained Increase

The hypothesis that an increase of calcium leads to activation of calcium-activated ionic conductances during cell swelling was examined in the isolated perfused proximal convoluted tubule of the rabbit. Reduction of bath and luminal osmolality by 90 mosmol/kgH2O caused the cells to swell by 23.6 +/- 1.5% (n = 5) and intracellular calcium to rise from 227 +/- 35 to 347 +/- 60 nM (n = 6). Both these increases were transient, with volume decreasing to 5.5 +/- 1.2% above control and intracellular calcium concentration decreasing to 272 +/- 46 nM after 5-9 min. The addition of glucose and alanine to the tubule lumen to increase transcellular sodium transport caused a sustained increase in cell volume of 15.6 +/- 3.4% (n = 4). In parallel experiments, no significant increase in intracellular calcium concentration was observed. Addition of 1 microM of the calcium ionophore, ionomycin, reversibly increased intracellular calcium by 224 +/- 60 nM from a control value of 301 +/- 29 nM (n = 7) and reversibly depolarized the basolateral membrane by 3.6 +/- 0.9 mV (n = 5). However, there was no initial increase in the apparent transference number for potassium or chloride and no significant change in cell volume. We conclude from these observations that the sustained increase in basolateral potassium conductance observed when cells are swollen by hypotonicity or increased sodium transport (J. S. Beck and D. J. Potts. J. Physiol. Lond. 425: 369-378, 1990) is not due to a calcium-activated potassium conductance.

Deafferentation increases the intracellular calcium of cochlear nucleus neurons in the embryonic chick

1995 ◽  
Vol 74 (3) ◽  
pp. 1355-1357 ◽  
Author(s):  
L. Zirpel ◽  
E. A. Lachica ◽  
W. R. Lippe
Keyword(s):  
Intracellular Calcium ◽  
Frequency Distribution ◽  
Cochlear Nucleus ◽  
Calcium Concentration ◽  
Embryonic Chick ◽  
In Ovo ◽  
Neuron Degeneration ◽  
Fura 2 ◽  
The Mean ◽  
Normal Input

1. Ratiometric fura-2 imaging was used to measure the intracellular calcium concentration ([Ca2+]i) of neurons in the embryonic avian cochlear nucleus, nucleus magnocellularis (NM), after an in ovo unilateral cochlea removal (deafferentation). 2. The mean [Ca2+]i of NM neurons receiving normal input was 113 nM. 3. Deafferentation increased the mean [Ca2+]i of NM neurons to 247, 311, 339, and 314 nM at 1, 3, 6, and 12 h after cochlear removal, respectively. These values did not differ significantly. 4. The percent frequency distribution of deafferented NM neuron [Ca2+]i shifts away from normative levels toward higher [Ca2+]i at 1 and 3 h after cochlear removal, but shifts back toward normative levels at 6 and 12 h after cochlear removal. 5. This increased [Ca2+]i following cochlear removal temporally coincides with well-characterized changes in NM neurons following activity deprivation. 6. These data suggest that deregulation of [Ca2+]i homeostasis plays a key role in NM neuron degeneration and death following activity deprivation.

Mechanisms of ACTH- and angiotensin II-stimulated 1α-hydroxycorticosterone secretion in the dogfish, Scyliorhinus canicula

1993 ◽  
Vol 10 (3) ◽  
pp. 235-244 ◽  
Author(s):  
K J Armour ◽  
L B O'Toole ◽  
N Hazon
Keyword(s):  
Angiotensin Ii ◽  
Cyclic Amp ◽  
Intracellular Calcium ◽  
Calcium Concentration ◽  
Extracellular Calcium ◽  
Scyliorhinus Canicula ◽  
Interrenal Gland ◽  
Messenger System ◽  
Dose Dependent Increase ◽  
Dose Dependent

ABSTRACT An isolated perifused interrenal gland preparation from the lesser-spotted dogfish, Scyliorhinus canicula, was used to investigate the mechanisms of action of ACTH and angiotensin II (AII) on elasmobranch adrenocortical cells. ACTH-stimulated 1α-hydroxycorticosterone secretion was unaffected by dantrolene and significantly decreased in the absence of extracellular calcium. Dibutyryl cyclic AMP produced a dose-dependent increase in 1α-hydroxycorticosterone secretion. The results suggest that the mechanism of ACTH action in elasmobranchs may be similar to that reported for mammals and amphibians, involving the synergistic action of calcium with the cyclic AMP messenger system. AII-stimulated 1α-hydroxycorticosterone secretion was significantly inhibited in the presence of dantrolene and in the absence of extracellular calcium, indicating that both extracellular and intracellular calcium are required for the full action of AII. These results are consistent with results in mammals and amphibians where AII stimulates phosphatidylinositol 4,5-bisphosphate hydrolysis and changes in intracellular calcium concentration, and they suggest that AII may operate via this mechanism to stimulate 1α-hydroxycorticosterone secretion in elasmobranchs.

Endothelial cell calcium increases during flow-induced dilation in isolated arterioles

1993 ◽  
Vol 264 (2) ◽  
pp. H653-H659 ◽  
Author(s):  
J. C. Falcone ◽  
L. Kuo ◽  
G. A. Meininger
Keyword(s):  
Endothelial Cells ◽  
Endothelial Cell ◽  
Endothelial Function ◽  
Intracellular Calcium ◽  
Digital Image ◽  
Calcium Concentration ◽  
Strong Support ◽  
Fluorescence Microscope ◽  
Fura 2 ◽  
Flow Through

The influence of flow on endothelial intracellular calcium concentration ([Ca2+]i) was determined in intact, isolated arterioles by selectively loading endothelial cells with the calcium-sensitive fluorescent dye fura-2. A fluorescence microscope coupled to a digital image processor was used to simultaneously measure fura-2 fluorescence and microvessel diameter. Flow through the arteriole significantly increased endothelial [Ca2+]i and dilated arterioles. Acetylcholine also increased in endothelial [Ca2+]i and caused vasodilation. In comparison, adenosine did not alter endothelial [Ca2+]i but dilated arterioles. Removal of the endothelium abolished the responses to flow and acetylcholine but not adenosine. These results provide strong support for the involvement of calcium in endothelium-dependent dilation of isolated arterioles by flow and agonists and emphasize the importance of studying endothelial function in intact vessels.

scholarly journals Endogenous and exogenous adenosine inhibit granulocyte aggregation without altering the associated rise in intracellular calcium concentration

Blood ◽  
1988 ◽  
Vol 72 (1) ◽  
pp. 29-33
Author(s):  
KM Skubitz ◽  
NW Wickham ◽  
DE Hammerschmidt
Keyword(s):  
Intracellular Calcium ◽  
Calcium Concentration ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Maximal Inhibition ◽  
Kinase C ◽  
Dose Dependent Fashion ◽  
Granulocyte Function ◽  
Dose Dependent

The effects of adenosine, adenosine deaminase (ADA), and an irreversible ADA inhibitor 2′-deoxycoformycin (DCF) on granulocyte aggregation in response to four different stimuli: the synthetic chemotaxin N-formyl-met-leu-phe (FMLP), zymosan-activated plasma (ZAP), the calcium ionophore A23187, and phorbol myristate acetate (PMA) were studied. Adenosine inhibited granulocyte aggregation in response to 10(- 7) mol/L FMLP in a dose-dependent fashion; inhibition in the presence of 1 mumol/L adenosine was 25% +/- 3% (SD) and was 50% (the maximal inhibition observed) with 1 mmol/L adenosine. Quantitatively similar results were obtained when ZAP or A23187 was used as the aggregant but the response to PMA was not affected. ADA not only reversed the inhibition due to adenosine but actually augmented the aggregation to FMLP by 118% +/- 9%. Similar results were obtained with ZAP and A23187 but not with PMA. These effects of ADA depended on its enzymatic activity as they could be blocked by preincubation with DCF. Fluorescent measurement of intracellular calcium in fura-2 loaded granulocyte suspensions established that neither adenosine nor ADA affected subsequent FMLP-stimulated calcium responses. Adenosine, therefore, may inhibit granulocyte responsiveness by blocking signal transduction at a point after calcium entry/mobilization but before activation of protein kinase C. Furthermore, the augmentation of responses seen with ADA suggests that endogenous adenosine may be a physiologic autocrine regulator of granulocyte function.

scholarly journals Endogenous and exogenous adenosine inhibit granulocyte aggregation without altering the associated rise in intracellular calcium concentration

Blood ◽  
1988 ◽  
Vol 72 (1) ◽  
pp. 29-33 ◽  
Author(s):  
KM Skubitz ◽  
NW Wickham ◽  
DE Hammerschmidt
Keyword(s):  
Intracellular Calcium ◽  
Calcium Concentration ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Maximal Inhibition ◽  
Kinase C ◽  
Dose Dependent Fashion ◽  
Granulocyte Function ◽  
Dose Dependent

Abstract The effects of adenosine, adenosine deaminase (ADA), and an irreversible ADA inhibitor 2′-deoxycoformycin (DCF) on granulocyte aggregation in response to four different stimuli: the synthetic chemotaxin N-formyl-met-leu-phe (FMLP), zymosan-activated plasma (ZAP), the calcium ionophore A23187, and phorbol myristate acetate (PMA) were studied. Adenosine inhibited granulocyte aggregation in response to 10(- 7) mol/L FMLP in a dose-dependent fashion; inhibition in the presence of 1 mumol/L adenosine was 25% +/- 3% (SD) and was 50% (the maximal inhibition observed) with 1 mmol/L adenosine. Quantitatively similar results were obtained when ZAP or A23187 was used as the aggregant but the response to PMA was not affected. ADA not only reversed the inhibition due to adenosine but actually augmented the aggregation to FMLP by 118% +/- 9%. Similar results were obtained with ZAP and A23187 but not with PMA. These effects of ADA depended on its enzymatic activity as they could be blocked by preincubation with DCF. Fluorescent measurement of intracellular calcium in fura-2 loaded granulocyte suspensions established that neither adenosine nor ADA affected subsequent FMLP-stimulated calcium responses. Adenosine, therefore, may inhibit granulocyte responsiveness by blocking signal transduction at a point after calcium entry/mobilization but before activation of protein kinase C. Furthermore, the augmentation of responses seen with ADA suggests that endogenous adenosine may be a physiologic autocrine regulator of granulocyte function.

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