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Biomedical subjects

M J Berridge

Publications and source records attributed to M J Berridge.

At least 109 records · Page 6Linked to original sources
PubMed1988

Effects of pertussis toxin on growth factor-stimulated inositol phosphate formation and DNA synthesis in Swiss 3T3 cells.

We have compared the effects of pretreatment of Swiss 3T3 cell with pertussis toxin on the stimulation of DNA synthesis and phosphoinositide hydrolysis in response to a wide variety of mitogens. The toxin substantially inhibited the stimulation of DNA synthesis in response to a phorbol ester or various peptide and polypeptide growth factors irrespective of their ability to activate phosphoinositidase C. Production of inositol phosphates in response to platelet-derived growth factor, fibroblast growth factor and prostaglandin F2 alpha were unaffected by the toxin while bombesin- and vasopressin-stimulated formation of inositol phosphates were inhibited by only 27 and 23% respectively. These results argue against a major role for a pertussis toxin-sensitive G protein in coupling any of these mitogen receptors to activation of a phosphoinositidase C. Furthermore, the results suggest that the widespread inhibitory effects of pertussis toxin on mitogen-stimulated DNA synthesis may be unrelated to the toxin's limited actions on phosphoinositide hydrolysis.

Animals↗
PubMed1988

DL-myo-inositol 1,4,5-trisphosphorothioate mobilizes intracellular calcium in Swiss 3T3 cells and Xenopus oocytes.

The initial water-soluble product of receptor-stimulate polyphosphoinositide hydrolysis, D-myo-inositol 1,4,5-trisphosphate is now accepted as the second messenger that stimulates release of Ca2+ from intracellular pools. We report here the first examples of Ca2+ release by a novel phosphatase-resistant inositol trisphosphate analogue, DL-myo-inositol 1,4,5-trisphosphorothioate, in Swiss 3T3 cells and Xenopus oocytes. L-myo-inositol 1,4,5-trisphosphate was inactive in the latter system.

Animals↗
PubMed1988

Cytosolic calcium oscillators.

Many cells display oscillations in intracellular calcium resulting from the periodic release of calcium from intracellular reservoirs. Frequencies are varied, but most oscillations have periods ranging from 5 to 60 s. For any given cell, frequency can vary depending on external conditions, particularly the concentration of natural stimuli or calcium. This cytosolic calcium oscillator is particularly sensitive to those stimuli (neurotransmitters, hormones, growth factors) that hydrolyze phosphoinositides to give diacylglycerol and inositol 1,4,5-trisphosphate (Ins1,4,5P3). The ability of Ins1,4,5P3 to mobilize intracellular calcium is a significant feature of many of the proposed models that are used to explain oscillatory activity. Receptor-controlled oscillator models propose that there are complex feedback mechanisms that generate oscillations in the level of Ins1,4,5P3. Second messenger-controlled oscillator models demonstrate that the oscillator is a component of the calcium reservoir, which is induced to release calcium by a constant input of either Ins1,4,5P3 or calcium itself. In the latter case, the process of calcium-induced calcium release might be the basis of oscillatory activity in many cell types. The function of calcium oscillations is still unknown. Because oscillator frequency can vary with agonist concentration, calcium transients might be part of a frequency-encoded signaling system. When an external stimulus arrives at the cell surface the information is translated into a train of calcium spikes, i.e., the signal is digitized. Certain cells may then convey information by varying the frequency of this digital signal.

Animals↗
PubMed1988

Inositol trisphosphate-induced membrane potential oscillations in Xenopus oocytes.

1. The role of inositol 1,4,5-trisphosphate (Ins1,4,5P3) in controlling the membrane potential oscillations induced by acetylcholine in Xenopus oocytes was investigated by studying the effect of injecting Ins1,4,5P3. 2. Perfusing Xenopus oocytes with low concentrations of acetylcholine (less than or equal to 1 x 10(-7) M) induced regular oscillations in membrane potential. The frequency of these oscillations accelerated as the concentration of acetylcholine was increased. 3. Ionophoretic application of low doses of Ins1,4,5P3 stimulated membrane depolarization in the form of an initial brief spike which was followed by a burst of oscillations when the amount of Ins1,4,5P3 injected was increased. 4. When low doses of Ins1,4,5P3 were injected at 30 s intervals, there was rapid desensitization of the early response which recovered if the interval between injections was extended to 2 min or longer. 5. In comparison to the vegetal pole, the animal pole was much more sensitive to Ins1,4,5P3. This localization of Ins1,4,5P3 sensitivity in the animal pole may contribute to the electrical field which surrounds Xenopus oocytes. 6. A model is presented to explain these oscillations based on the phenomenon of calcium-induced calcium release. It is proposed that Ins1,4,5P3 releases calcium from an Ins1,4,5P3-sensitive pool which is then periodically taken up and released by an Ins1,4,5P3-insensitive pool. It is the overloading of this Ins1,4,5P3-insensitive pool which may provide the trigger to spontaneously release calcium back into the cytoplasm.

Acetylcholine↗
PubMed1988

Control of secretion in anterior pituitary cells--linking ion channels, messengers and exocytosis.

Normal anterior pituitary cells, in their diversity and heterogeneity, provide a rich source of models for secretory function. However, until recently they have largely been neglected in favour of neoplastic, clonal tumour cell lines of pituitary origin, which have enabled a number of studies on supposedly homogeneous cell types. Because many of these lines appear to lack key peptide and neurotransmitter receptors, as well as being degranulated with accompanying abnormal levels of secretion, we have developed a range of normal primary anterior pituitary cell cultures using dispersion and enrichment techniques. By studying lactotrophs, somatotrophs and gonadotrophs we have revealed a number of possible transduction mechanisms by which receptors for hypothalamic peptides and neurotransmitters may control secretion. In particular, the transduction events controlling secretion from pituitary cells may differ fundamentally from those found in other cell types. Patch-clamp recordings in these various pituitary cell preparations have revealed substantial populations of voltage-dependent Na+, Ca2+ and K+ channels which may support action potentials in these cells. Although activation of these channels may gate Ca2+ entry to the cells under some conditions, our evidence taken with that of other laboratories suggests that peptide-receptor interactions leading to hormone secretion occur independently of significant membrane depolarization. Rather, secretion of hormone and rises in intracellular calcium measured with new probes for intracellular calcium activity, can occur in response to hypothalamic peptide activation in the absence of substantial changes in membrane potential. These changes in intracellular calcium activity almost certainly depend on both intracellular and extracellular calcium sources. In addition, strong evidence of a role for multiple intracellular receptors and modulators in the secretory event suggests we should consider the plasma membrane channels important for regulation of hormone secretion to be predominantly agonist-activated, rather than of the more conventional voltage-dependent type. Likewise, evidence from new methods for recording single ion channels suggests the existence of intracellular sites for channel modulation, implying they too may play an important role in secretory regulation. We shall consider new data and new technology which we hope will provide key answers to the many intriguing questions surrounding the control of pituitary hormone secretion. We shall highlight our work with recordings of single ion channels activated by peptides, and recent experiments using imaging of intracellular ionized free calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Inositol lipids and DNA replication.

Control of DNA synthesis by growth factors seems to depend upon the generation of intracellular mitogenic signals, which are responsible for initiating the sequence of events leading to the onset of DNA synthesis. Many growth factors have tyrosine kinase activity suggesting the proteins phosphorylated on tyrosine might be likely candidates as intracellular signals. Other candidates are the calcium and hydrogen ions whose concentrations change dramatically during the action of most growth factors, many of which also stimulate the hydrolysis of inositol lipids. In particular, certain growth factors stimulate the hydrolysis of phosphatidylinositol 4,5-bisphosphate to give the two second messengers diacylglycerol and inositol 1,4,5-trisphosphate (Ins1,4,5P3). The former stimulates protein kinase C, which is responsible for increasing intracellular pH by switching on an Na+-H+ exchanger. The water-soluble Ins1,4,5P3 released to the cytosol can be metabolized along two separate pathways: it can either be dephosphorylated to free inositol or it can be converted into additional inositol polyphosphates such as Ins1,3,4,5P4 and Ins1,3,4P3. These inositol phosphates seem to play a key role in regulating intracellular calcium, with Ins1,4,5P3 functioning to release internal calcium, whereas Ins1,3,4,5P4 may function to regulate the entry of external calcium. There is evidence to suggest that these internal messengers may converge on certain key processes responsible for initiating the programme of cell growth. It is argued that an increase in intracellular calcium might be an important intracellular signal for activating both the transcription of a family of early genes, typified by fos, as well as the enzyme S6 kinase, which phosphorylates the ribosomal protein S6 which may regulate protein synthesis. The increase in pH seems to play a permissive role and may create the necessary ionic milieu for S6 phosphorylation and protein synthesis to occur. The onset of RNA and protein synthesis, which occur within the first few minutes after the arrival of a growth factor, represent the initial events of the programme of cell growth which culminates in DNA synthesis and cell division.

Animals↗
PubMed1987

Subsecond and second changes in inositol polyphosphates in GH4C1 cells induced by thyrotropin-releasing hormone.

It has been demonstrated previously that thyrotropin-releasing hormone (TRH) induces changes in inositol polyphosphates in the GH3 and GH4C1 strains of rat pituitary cells within 2.5-5.0 s. TRH also causes a rapid rise in cytosolic free calcium concentration ([Ca2+]i) in these cells which is due largely to redistribution of cellular calcium stores. Therefore, it has been concluded that TRH acts to release sequestered calcium in these cells via enhanced generation of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. If this conclusion were correct, TRH-enhanced accumulation of Ins(1,4,5)P3 should occur at least as rapidly as the increase in [Ca2+]i. We have shown previously that the rise in [Ca2+]i induced by TRH occurs within about 400 ms; thus, it was important to investigate the subsecond time-course of changes in inositol phosphates caused by TRH. Using a rapid mixing device, we have measured changes in inositol polyphosphates on a subsecond time scale in GH4C1 cells prelabelled with myo-[2-3H]inositol. Although TRH did alter inositol polyphosphate metabolism within 500 ms, the changes observed did not reveal a statistically significant increase in Ins(1,4,5)P3 within time intervals of less than 1000 ms. Thus, we have been unable to demonstrate that a TRH-induced rise in Ins(1,4,5)P3 precedes or occurs concomitantly with the rise in [Ca2+]i in GH4C1 cells. Although these results do not disprove the current view that Ins(1,4,5)P3 mediates the action of TRH on intracellular calcium redistribution, we conclude that caution should be exercised in this, and possibly other cell systems, in accepting the dogma that all of the rapid, agonist-induced redistributions of intracellular calcium are mediated by Ins(1,4,5)P3.

Animals↗
PubMed1987

Inositol(3,4)bisphosphate and inositol(1,3)bisphosphate in GH4 cells--evidence for complex breakdown of inositol(1,3,4)trisphosphate.

Analysis of inositol bisphosphates in GH4 cells labelled with [3H]myo-inositol shows that these cells contain three detectable inositol bisphosphates: inositol(1,4)bisphosphate, and two novel inositol bisphosphates. These latter inositol bisphosphates were degraded by periodate oxidation, borohydride reduction and alkaline phosphatase dephosphorylation; each yielded single non-cyclic alditols, ribitol and threitol, indicating that they must be respectively inositol(1,3)bisphosphate and inositol(3,4) bisphosphate. These two inositol bisphosphates are putative breakdown products of inositol(1,3,4)trisphosphate, and their occurrence suggests a complex route of hydrolysis of inositol(1,3,4)trisphosphate in intact cells.

Animals↗
PubMed1986

Effects of bombesin and insulin on inositol (1,4,5)trisphosphate and inositol (1,3,4)trisphosphate formation in Swiss 3T3 cells.

The effects of bombesin and insulin, separately and in combination, have been studied in Swiss mouse 3T3 cells. Bombesin caused a rapid transfer of 3H from the lipid inositol pool of prelabeled cells into inositol phosphates. Label in inositol tetrakisphosphate (InsP4) and in Ins1,4,5P3 and Ins1,3,4P3 rose within 10 sec of stimulation and that in Ins1,4P2, another InsP2 and InsP1, more slowly. Insulin, which had little effect on its own, increased the turnover of inositol lipids due to acute bombesin stimulation and also enhanced the DNA synthesis evoked by prolonged bombesin treatment. The results suggest that bombesin acting as a growth factor, uses inositol lipids as part of its transduction mechanism and that insulin acts synergistically to enhance both inositol phosphate formation and DNA synthesis.

Animals↗
PubMed1986

Specificity of inositol phosphate-stimulated Ca2+ mobilization from Swiss-mouse 3T3 cells.

Pure samples of inositol 1,3,4-trisphosphate, inositol 1,3,4,5-tetrakisphosphate and inositol 1,2-cyclic 4,5-trisphosphate were prepared and tested for their ability to mobilize calcium from intracellular stores in a permeabilized Swiss mouse 3T3 cell preparation. In this system inositol 1,4,5-trisphosphate mobilizes Ca2+ with a half-maximal dose of 0.3 microM. Inositol 1,2-cyclic 4,5-trisphosphate mobilized Ca2+ to the same extent with a half-maximal dose of 0.3 microM, whereas inositol 1,3,4-trisphosphate required a half-maximal dose of approx. 9 microM to give the same effect. Inositol 1,3,4,5-tetrakisphosphate was ineffective up to 20 microM and at that concentration did not antagonize the mobilization induced by inositol 1,4,5-trisphosphate. The relevance of these findings to the function of the inositol tris/tetrakis-phosphate pathway is discussed.

Animals↗
PubMed1986

Inositol trisphosphate and calcium mobilization.

Calcium-mobilizing agonists act by stimulating the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2) to inositol 1,4,5-trisphosphate and diacylglycerol (DG). In response to such agonists cells also produce inositol 1,3,4-trisphosphate but this isomer is unlikely to influence calcium mobilization. Application of inositol 1,4,5-trisphosphate (Ins1,4,5P3) to permeabilized cells results in a rapid release of calcium from the endoplasmic reticulum. Structure-activity studies reveal that the vicinal phosphates on the 4- and 5-positions are essential for releasing calcium whereas the phosphate on the opposite side enhances the affinity of Ins1,4,5P3 for its putative receptor. The flow of calcium across the endoplasmic reticulum appears to be electrogenic and requires an opposite flow of potassium to neutralize charge movements. Diacylglycerol, acting through protein kinase C, does not play a direct role in calcium signalling but it does modulate various aspects of the InsP3/Ca2+ pathway. The DG/protein kinase C pathway can influence both the formation and hydrolysis of PtdIns4,5P2 and can alter the responsiveness of various processes to the action of calcium. The Ins1,4,5P3/Ca2+ signal pathway functions throughout the life history of cells to regulate such diverse activities as egg maturation and fertilization, growth, secretion, metabolism, neural activity, and perhaps excitation-contraction coupling in skeletal muscle.

Animals↗
PubMed1986

Excitation and adaptation of Limulus ventral photoreceptors by inositol 1,4,5 triphosphate result from a rise in intracellular calcium.

Single pressure injections of 1-10 pl of inositol 1,4,5 triphosphate (IP3) or inositol 4,5 bisphosphate [I(4,5)P2] excite Limulus ventral photoreceptors by inducing rapid bursts of inward current. After excitation by IP3, responses to subsequent injections of IP3 or light flashes are often reversibly diminished (adapted). Single injections of IP3 and I(4,5)P2 are effective at concentrations in the injecting pipette of 20 microM to 1 mM. Single injections of inositol 1,4 bisphosphate are ineffective at concentrations of 100-500 microM. Excitation by IP3 or I(4,5)P2 is accompanied by a rise in intracellular free calcium, as indicated by aequorin luminescence. Prior injection of calcium buffer solutions containing 100 mM EGTA greatly diminishes the total charge transferred across the plasma membrane during excitation by IP3 or I(4,5)P2, which suggests that a rise in Cai is necessary for excitation by the inositol polyphosphates. Adaptation of the response to light by IP3 is also abolished by prior injection of EGTA. In the same cells, the response to brief light flashes is slowed and diminished in amplitude by the injection of calcium buffer, but the charge transferred during the response is not significantly diminished. This suggests that light has access to a pathway of excitation in the presence of EGTA that is not accessible to intracellularly injected IP3.

Adaptation, Physiological↗