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M J Berridge

Publications and source records attributed to M J Berridge.

At least 73 records · Page 4Linked to original sources
PubMed1993

Quantal Ca2+ release from caffeine-sensitive stores in adrenal chromaffin cells.

In populations of fura-2-loaded chromaffin cells, caffeine caused a concentration-dependent increase in the intracellular Ca2+ concentration ([Ca2+]i), in the presence or absence of external Ca2+ ([Ca2+]o), that was saturable, reversible, and inhibited in a use-dependent fashion by ryanodine. These data confirm that caffeine mobilizes Ca2+ from the ryanodine-sensitive intracellular stores in chromaffin cells. In nominally Ca(2+)-free medium, sustained stimulation of cell populations or single cells with low caffeine concentrations failed to completely empty the caffeine-sensitive stores. In each case, there was a transient [Ca2+]i elevation, but a subsequent challenge with a higher caffeine concentration evoked a further [Ca2+]i rise, indicating that Ca2+ stores within individual cells were heterogeneous in their sensitivities to caffeine and that caffeine-induced Ca2+ release was quantal. The heterogeneous sensitivity was also demonstrated using ryanodine; pretreatment of cell populations with increasing caffeine concentrations with a constant ryanodine concentration, caused a dose-dependent irreversible inhibition of the response to the subsequent addition of a maximal caffeine concentration. We conclude that, within single chromaffin cells, intracellular Ca2+ stores are heterogeneous in their sensitivity to caffeine and the fraction of Ca2+ stores mobilized by caffeine increases in direct proportion to the caffeine concentration.

Adrenal Medulla↗
PubMed1993

The role of endoplasmic reticulum calcium pumps during cytosolic calcium spiking in pancreatic acinar cells.

Many cell types show repetitive short lasting cytosolic calcium spikes with long interspike periods when stimulated with submaximal concentrations of agonists linked to the phosphoinositide signaling pathway. In pancreatic acinar cells these spikes have been shown to be evoked by constant levels of inositol trisphosphate through a mechanism of calcium-induced calcium release and do not depend acutely on the presence of external calcium. However, the processes involved in the interspike period have remained unclear. Here we report that the endoplasmic reticulum Ca(2+)-ATPase play a significant role, not only in resequestering calcium after a spike, but also in regulating the long interspike period. Decreasing the activity of the endoplasmic reticulum calcium pumps leads to shorter interspike intervals and thus higher spiking frequencies, while the duration of each spike increases. The endoplasmic reticulum Ca(2+)-ATPases are able to entirely suppress a response that can subsequently be evoked by partial inhibition of the pumps. This suggests that during the interspike period there is a considerable amount of calcium released from intracellular stores, which is rapidly buffered by the endoplasmic reticulum calcium pumps and the cytosolic calcium-binding proteins. A calcium spike will be initiated by calcium-induced calcium release only when the buffering is saturated.

Animals↗
PubMed1993

Inositol trisphosphate and calcium signalling.

Inositol trisphosphate is a second messenger that controls many cellular processes by generating internal calcium signals. It operates through receptors whose molecular and physiological properties closely resemble the calcium-mobilizing ryanodine receptors of muscle. This family of intracellular calcium channels displays the regenerative process of calcium-induced calcium release responsible for the complex spatiotemporal patterns of calcium waves and oscillations. Such a dynamic signalling pathway controls many cellular processes, including fertilization, cell growth, transformation, secretion, smooth muscle contraction, sensory perception and neuronal signalling.

Animals↗
PubMed1993

Fertilisation and thimerosal stimulate similar calcium spiking patterns in mouse oocytes but by separate mechanisms.

Exposure of freshly ovulated mouse oocytes to a fertilising spermatozoon, thimerosal, Sr2+ or acetylcholine induced similar Ca2+ spiking responses. We propose that each of the four agents reduces the threshold for Ca2+ release from internal stores, but by different mechanisms. All agents except thimerosal stimulated oocyte activation, but thimerosal caused dissassembly of the meiotic spindle and thus prevented progress into interphase. Dithiothreitol (DTT) completely blocked and reversed the spiking responses induced by thimerosal, but facilitated and accelerated those induced by spermatozoa, Sr2+ and acetylcholine. The stimulatory effect of DTT was not simply a consequence of progress into interphase, but was attributable, at least in part, to an enhancement of divalent cation entry, as measured by Mn2+ quench analysis of fura-2 in both fertilised and unfertilised oocytes. Possible mechanisms by which DTT might achieve its effects are discussed.

Animals↗
PubMed1993

Spatial localization of agonist-induced Ca2+ entry in bovine adrenal chromaffin cells. Different patterns induced by histamine and angiotensin II, and relationship to catecholamine release.

The spatial organization of agonist-induced Ca2+ entry in single bovine adrenal chromaffin cells has been investigated using video-imaging techniques to visualize fura-2 quenching by the Ca2+ surrogate, Mn2+. The potent secretagogue histamine, in addition to releasing Ca2+ from intracellular stores, resulted in a large influx of external Mn2+ that occurred over the entire surface of the cell. The influx of Ca2+ that this mirrors was found to be an obligatory requirement for the triggering of catecholamine release by histamine, which suggests that such a global influx of Ca2+ into the cell probably underlies the ability of this agonist to stimulate a large secretory response. By contrast, the weaker secretagogue angiotensin II, which also acts through the second messenger inositol trisphosphate, produced a localized entry of external Mn2+ in 64% of cells. In these cells, localized Mn2+ entry always occurred at the pole of the cell in which the angiotensin II-induced rise in [Ca2+]i was largest. Since exocytosis in response to angiotensin II has previously been shown to be restricted to this same pole of the cell (Cheek et al. (1989). J. Cell Biol. 109, 1219-1227), these results suggest that localized influx of Ca2+ in response to angiotensin II could underlie the polarized exocytotic response observed with this stimulus. These results directly demonstrate that different agonists can induce different patterns of divalent cation influx in the same cells and, furthermore, suggest how these different patterns can have a direct influence on cellular function.

Adrenal Medulla↗
PubMed1992

The thiol reagent, thimerosal, evokes Ca2+ spikes in HeLa cells by sensitizing the inositol 1,4,5-trisphosphate receptor.

The thiol reagent, thimerosal, has been shown to cause an increase in intracellular Ca2+ concentration ([Ca2+]i) in several cell types, and to cause Ca2+ spikes in unfertilized hamster eggs. Using single cell video-imaging we have shown that thimerosal evokes repetitive Ca2+ spikes in intact Fura-2-loaded HeLa cells that were similar in shape to those stimulated by histamine. Both thimerosal- and histamine-stimulated Ca2+ spikes occurred in the absence of extracellular (Ca2+ o), suggesting that they result from mobilization of Ca2+ from intracellular stores. Whereas histamine stimulated formation of inositol phosphates, thimerosal, at concentrations that caused sustained Ca2+ spiking, inhibited basal and histamine-stimulated formation of inositol phosphates. Thimerosal-evoked Ca2+ spikes are therefore not due to the stimulated production of inositol 1,4,5-trisphosphate (InsP3). The effects of thimerosal on Ca2+ spiking were probably due to alkylation of thiol groups on intracellular proteins because the spiking was reversed by the thiol-reducing compound dithiothreitol, and the latency between addition of thimerosal and a rise in [Ca2+]i was greatly shortened in cells where the intracellular reduced glutathione concentration had been decreased by preincubation with DL-buthionine (S,R)-sulfoximine. In permeabilized cells, thimerosal caused a concentration-dependent inhibition of Ca2+ accumulation, which was entirely due to inhibition of Ca2+ uptake into stores because thimerosal did not affect unidirectional 45Ca2+ efflux from stores preloaded with 45Ca2+. Thimerosal also caused a concentration-dependent sensitization of InsP3-induced Ca2+ mobilization: half-maximal mobilization of Ca2+ stores occurred with 161 +/- 20 nM InsP3 in control cells and with 62 +/- 5 nM InsP3 after treatment with 10 microM thimerosal. We conclude that thimerosal can mimic the effects of histamine on intracellular Ca2+ spiking without stimulating the formation of InsP3 and, in light of our results with permeabilized cells, suggest that thimerosal stimulates spiking by sensitizing cells to basal InsP3 levels.

Calcium↗
PubMed1992

All-or-nothing Ca2+ mobilization from the intracellular stores of single histamine-stimulated HeLa cells.

1. Histamine-stimulated mobilization of intracellular Ca2+ stores was monitored in intact and permeabilized populations of HeLa cells using both the fluorescent Ca2+ indicator Fura-2 and 45Ca2+ measurements. Digital video imaging of Fura-2-loaded cells was used to measure the intracellular calcium concentration ([Ca2+]i) of single cells. 2. In populations of HeLa cells, histamine caused a concentration-dependent increase in cytoplasmic [Ca2+]. The initial transient increase was independent of extracellular Ca2+ (Ca2+o) and was followed by a sustained increase that was abolished by removal of Ca2+o. 3. In Ca(2+)-free medium ([Ca2+]o < 1 microM), a maximal histamine concentration (25 microM) caused a transient increase in [Ca2+]i, and a subsequent challenge with histamine failed to evoke a further response indicating that the inositol 1,4,5-trisphosphate (InsP3)-sensitive Ca2+ stores had been completely emptied. Lower concentrations of histamine (0.5-10 microM) caused smaller, concentration-dependent increases in [Ca2+]i that were also transient. After exposure to these low histamine concentrations, where [Ca2+]i returned to baseline within 2 min, addition of a higher histamine concentration evoked a further increase in [Ca2+]i. The second increase in [Ca2+]i was inversely proportional to the increase caused by the first exposure to histamine, indicating that Ca2+ released in the initial response was not substantially resequestered into histamine-sensitive stores. 4. Single HeLa cells challenged with low concentrations of histamine in Ca(2+)-free medium responded with transient increases in [Ca2+]i, but individual cells differed in their sensitivity with 51% of cells responding to 1 microM, and 98% responding to 25 microM-histamine. 5. When single cells in Ca(2+)-free medium were challenged with stepwise increases in histamine concentration, they responded to each step with a transient [Ca2+]i increase after which [Ca2+]i returned to baseline within 1 min. Prolonging the interval between histamine additions by up to 25 min did not affect the [Ca2+]i increase evoked by a subsequent histamine addition. 6. Unidirectional 45Ca2+ efflux from saponin-permeabilized HeLa cells showed that, under conditions that prevented Ca2+ resequestration, submaximal concentrations of InsP3 rapidly emptied only a fraction of the InsP3-sensitive Ca2+ stores. The failure of low InsP3 concentrations to fully mobilize the InsP3-sensitive Ca2+ stores was not a consequence of InsP3 degradation. 7. We conclude that within single HeLa cells, intracellular Ca2+ stores are heterogeneous in their sensitivity to InsP3, and the fraction of Ca2+ stores mobilized by InsP3 increases as the InsP3 concentration increases.

Biological Transport↗
PubMed1992

Luminal Ca2+ promoting spontaneous Ca2+ release from inositol trisphosphate-sensitive stores in rat hepatocytes.

1. Spontaneous Ca2+ release from the inositol 1,4,5-trisphosphate (InsP3)-sensitive stores in permeabilized hepatocytes was monitored using Fluo-3 to measure the free [Ca2+] of the medium bathing the cells. 2. Permeabilized cells rapidly sequestered Ca2+, reducing the [Ca2+] to 103 +/- 5 nM. Under conditions that depended critically upon cell density and the amount of Ca2+ in the medium, this was followed by a slow increase in [Ca2+] culminating in a substantial Ca2+ spike representing synchronous discharge from the InsP3-sensitive stores. 3. During the latency preceding the Ca2+ spike, the stores increased their sensitivity to InsP3. This sensitization seemed to be an all-or-none phenomenon. 4. Oxidized glutathione and thimerosal promoted the spontaneous release by sensitizing the InsP3 receptor. 5. An increase in the [Ca2+] within the stores was required for both the increased sensitivity to InsP3 and the subsequent spike. 6. Caffeine (6 mM) antagonized the effect of very low InsP3 concentrations and abolished the Ca2+ spike, without itself releasing Ca2+. 7. Our results suggesting that luminal Ca2+ may sensitive InsP3-sensitive stores leading to spontaneous Ca2+ mobilization will be discussed in the light of a modified version of the two-pool model for explaining cytosolic Ca2+ oscillations.

Action Potentials↗
PubMed1991

Spontaneous calcium release from inositol trisphosphate-sensitive calcium stores.

Inositol 1,4,5-trisphosphate (InsP3) functions as a second messenger to mobilize Ca2+ from intracellular reservoirs. The release mechanism displays all-or-none characteristics, that may account for other observations that the InsP3-induced mobilization of Ca2+ is quantal. Quantal release may depend on the sensitivity of the InsP3 receptor being regulated by the Ca2+ concentration in the lumen of the endoplasmic reticulum. We report here that the InsP3-sensitive store in hepatocytes discharges spontaneously when overloaded with Ca2+. The release, which is blocked by heparin, is preceded by an increasing sensitivity of the InsP3 receptor to endogenous InsP3, and is promoted by those sulphydryl reagents (oxidized glutathione and thimerosal) that induce Ca2+ oscillations in intact cells (ref. 8, and T. A. Rooney, D. C. Renard, E. J. Sass and A. P. Thomas, manuscript in preparation). This novel process could have a role in generating both Ca2+ oscillations and Ca2+ waves.

Animals↗
PubMed1991

Bovine adrenal chromaffin cells contain an inositol 1,4,5-trisphosphate-insensitive but caffeine-sensitive Ca2+ store that can be regulated by intraluminal free Ca2+.

We have characterized some properties of the caffeine-sensitive Ca2+ store in bovine chromaffin cells. Addition of 10 mM-caffeine to permeabilized cells that were allowed to sequester Ca2+ in the presence of the precipitating anion pyrophosphate induced a transient rise in free Ca2+ concentration that was blocked by 10 microM-Ruthenium Red. Caffeine was able to release Ca2+ after the InsP3-sensitive Ca2+ pool had been completely emptied, and 10 microM-InsP3 still released Ca2+ in the presence of a high dose (50 mM) of caffeine, indicating that there are selectively sensitive Ca2+ pools in these cells. The progressive hydrolysis of pyrophosphate by a cytosolic pyrophosphatase induced a spontaneous Ca2+ release after a latency. Caffeine prevented this spontaneous Ca2+ release, indicating that the pyrophosphate-sensitive Ca2+ pool was caffeine-sensitive. On varying the free Ca2+ concentration within the caffeine-sensitive pool (by using methylenediphosphonic acid, pyrophosphate or no precipitating anion), we observed that the Ca(2+)-releasing effect of caffeine was dependent on an elevated intraluminal free Ca2+ concentration. In conclusion, the caffeine-sensitive Ca2+ store in bovine chromaffin cells is largely distinct from the InsP3-sensitive Ca2+ store, and its release mechanism shares characteristics with the ryanodine receptor of muscle cells.

Adrenal Medulla↗
PubMed1991

Caffeine inhibits inositol-trisphosphate-induced membrane potential oscillations in Xenopus oocytes.

Immature Xenopus oocytes injected with inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) give a complex electrophysiological response comprising an a early depolarizing spike followed by a burst of oscillations. These two components have been interpreted on the basis of an interaction between two internal calcium stores: an Ins(1,4,5) P3-sensitive pool responsible for the early spike which then primes an Ins(1,4,5) P3-insensitive pool to begin to oscillate through a process of calcium-induced calcium release (Berridge, M. J., J. Physiol., Lond. 403, 589-599 (1988)). The role of the latter was investigated in Xenopus oocytes by using the drug caffeine which can trigger calcium-induced calcium release in muscle cells. Caffeine had no effect on the early Ins(1,4,5)P3-induced spike but it suppressed the subsequent oscillations. The spontaneous oscillations observed in some oocytes were also abolished by caffeine. Oscillation amplitude and duration was slightly reduced following incubation of oocytes with adenosine or isobutylmethylxanthine. Because these two agents gave large membrane hyperpolarizations indicative of an increase in cyclic AMP, it can be concluded that this second messenger is not responsible for the inhibitory action of caffeine. The ability of caffeine to abolish oscillations while not affecting the early Ins(1,4,5) P3 response is discussed with regard to the two-pool model for generating calcium oscillations.

Animals↗
PubMed1991

Fura-2 imaging of thyrotropin-releasing hormone and dopamine effects on calcium homeostasis of bovine lactotrophs.

Dual wavelength digital imaging microscopy to detect fura-2 has been employed to characterize in normal bovine PRL-secreting cells the effects of TRH and dopamine on the intracellular ionized calcium concentration [( Ca2+]i). Concentrations of TRH greater than 10 nM caused a rapid but transient increase in [Ca2+]i, arising mainly from intracellular calcium stores, since it was unaffected by lowering extracellular calcium with EGTA or blocking calcium channels with Co2+. The threshold for TRH action was close to 0.1 nM. TRH action was dose dependent, with lower concentrations (less than 1-10 nM) slowing the time to peak [Ca2+]i response. The TRH-induced [Ca2+]i rise had a Q10 of about 2. TRH caused multiple transient increases in [Ca2+]i, but a recovery time of 10-15 min was required for full restoration of the TRH-induced response. In some cells the [Ca2+]i response to TRH was polarized to one region of the cell, suggesting the following possibilities, none of them exclusive: 1) Ca2+ release sites may be localized within the cell; or 2) an efficient local mechanism exists for lowering Ca2+ once it is liberated inside the cells; or 3) barriers may exist to diffusion of Ca2+ released within the cell. Extracellular application of Co2+, Mn2+, and EGTA under basal conditions resulted in lowering of [Ca2+]i within seconds, consistent with tonic Ca2+ influx under resting conditions which could contribute to the basal release of hormone. Dopamine, a PRL release-inhibiting factor, also lowered [Ca2+]i under basal conditions. However, the [Ca2+]i response of lactotrophs to TRH was unaffected by dopamine. This suggests that dopamine and TRH act via separate intracellular pathways to modulate hormone secretion. Applications of forskolin preceding the TRH-induced transient rise in [Ca2+]i resulted in a prolonged plateau rise in [Ca2+]i. This was mainly due to increased influx of Ca2+ since addition of Co2+ or EGTA-containing or Ca(2+)-free medium during this phase of response lowered the plateau concentration of [Ca2+]i.

Animals↗