Inositol Trisphosphate Concentration Research Articles

On the dynamical structure of calcium oscillations

Oscillations in the concentration of free cytosolic Ca2+ are an important and ubiquitous control mechanism in many cell types. It is thus correspondingly important to understand the mechanisms that underlie the control of these oscillations and how their period is determined. We show that Class I Ca2+ oscillations (i.e., oscillations that can occur at a constant concentration of inositol trisphosphate) have a common dynamical structure, irrespective of the oscillation period. This commonality allows the construction of a simple canonical model that incorporates this underlying dynamical behavior. Predictions from the model are tested, and confirmed, in three different cell types, with oscillation periods ranging over an order of magnitude. The model also predicts that Ca2+ oscillation period can be controlled by modulation of the rate of activation by Ca2+ of the inositol trisphosphate receptor. Preliminary experimental evidence consistent with this hypothesis is presented. Our canonical model has a structure similar to, but not identical to, the classic FitzHugh-Nagumo model. The characterization of variables by speed of evolution, as either fast or slow variables, changes over the course of a typical oscillation, leading to a model without globally defined fast and slow variables.

Characterization and modeling of Ca2 + oscillations in mouse primary mesothelial cells

Brief changes in the cytosolic and intra-organellar Ca2+ concentration serve as specific signals for various physiological processes. In mesothelial cells lining the surface of internal organs and the walls of body cavities, a re-entry in the cell cycle (G0–G1 transition) evoked by serum re-administration induces long-lasting Ca2+ oscillations with a slowly decreasing frequency. Individual mesothelial cells show a wide range of different oscillatory patterns within a single, supposedly homogenous cell population. Changes in the cytoplasmic Ca2+ concentration (ccyt) show baseline oscillatory patterns i.e., discrete Ca2+ transients starting from a constant basal ccyt level. The ER Ca2+ concentration (cER) displays a sawtooth wave at a semi-depleted ER state; the minimum level is reached just briefly after the maximal value for ccyt. These oscillations depend on plasmalemmal Ca2+ influx and on the inositol trisphosphate concentration [InsP3]; the Ca2+ influx is a crucial determinant of the oscillation frequency. Partial blocking of SERCA pumps modifies the oscillation frequency in both directions, i.e. increasing it in some cells and lowering it in others. Current mathematical models for Ca2+ oscillations mostly fail to reproduce two experimentally observed phenomena: the broad range of interspike intervals and constant basal ccyt levels between two Ca2+ spikes. Here we developed a new model based on – and fitted to – Ca2+ recordings of ccyt and cER recorded in primary mouse mesothelial cells. The model allowed for explaining many features of experimentally observed Ca2+ oscillations. We consider this model to be suitable to simulate various types of InsP3 receptor-based baseline Ca2+ oscillations.

Dynamical Analysis of a Calcium Oscillation Model in Non-Excitable Cells

The Borghans-Dupont model of calcium oscillations based on both the calcium-induced calcium release and calcium-activated inositol trisphosphate concentration degradation is considered. Dynamical effect of the stimulation level on the calcium oscillation behavior is studied. The qualitative theory of differential equations is used to explain the mechanism of these oscillations. We investigate the existence, types, stability and bifurcations of the equilibria by applying the centre manifold theorem, stability theory and bifurcation theory and prove that oscillations are due to supercritical Hopf bifurcation. Finally, we perform numerical simulations, including time courses, phase portraits and bifurcation diagram, to validate the correctness and the effectiveness of our theoretical analysis. These results may be instructive for understanding the role of the stimulation level played in complex dynamics in this model.

A Kinetic Model for Type I and II IP3R Accounting for Mode Changes

Based upon an extensive single-channel data set, a Markov model for types I and II inositol trisphosphate receptors (IP3R) is developed. The model aims to represent accurately the kinetics of both receptor types of IP3R depending on the concentrations of inositol trisphosphate (IP3), adenosine trisphosphate (ATP), and intracellular calcium (Ca2+). In particular, the model takes into account that for some combinations of ligands the IP3R switches between extended periods of inactivity alternating with intervals of bursting activity (mode changes). In a first step, the inactive and active modes are modeled separately. It is found that, within modes, both receptor types are ligand-independent. In a second step, the submodels are connected by transition rates. Ligand-dependent regulation of the channel activity is achieved by modulating these transitions between active and inactive modes. As a result, a compact representation of the IP3R is obtained that accurately captures stochastic single-channel dynamics including mode changes in a model with six states and 10 rate constants, only two of which are ligand-dependent.

MGluR-Mediated Calcium Waves that Invade the Soma Regulate Firing in Layer V Medial Prefrontal Cortical Pyramidal Neurons

Factors that influence the activity of prefrontal cortex (PFC) pyramidal neurons are likely to play an important role in working memory function. One such factor may be the release of Ca2+ from intracellular stores. Here we investigate the hypothesis that metabotropic glutamate receptors (mGluRs)-mediated waves of internally released Ca2+ can regulate the intrinsic excitability and firing patterns of PFC pyramidal neurons. Synaptic or focal pharmacological activation of mGluRs triggered Ca2+ waves in the dendrites and somata of layer V medial PFC pyramidal neurons. These Ca2+ waves often evoked a transient SK-mediated hyperpolarization followed by a prolonged depolarization that respectively decreased and increased neuronal excitability. Generation of the hyperpolarization depended on whether the Ca2+ wave invaded or came near to the soma. The depolarization also depended on the extent of Ca2+ wave propagation. We tested factors that influence the propagation of Ca2+ waves into the soma. Stimulating more synapses, increasing inositol trisphosphate concentration near the soma, and priming with physiological trains of action potentials all enhanced the amplitude and likelihood of evoking somatic Ca2+ waves. These results suggest that mGluR-mediated Ca2+ waves may regulate firing patterns of PFC pyramidal neurons engaged by working memory, particularly under conditions that favor the propagation of Ca2+ waves into the soma.

A simple and practical method to acquire geometrically correct images with resonant scanning‐based line scanning in a custom‐built video‐rate laser scanning microscope

Most currently available confocal or two-photon laser scanning microscopes (LSMs) allow acquisition rates of the order of 1-5 images s(-1), which is too slow to fully resolve dynamic changes in intracellular messenger concentration in living cells or tissues. Several technologies exist to obtain faster imaging rates, either in the video-rate range (30 images s(-1)) or beyond, but the most versatile technology available today is based on resonant scanners for horizontal line scanning. These scanning devices have several advantages over designs based on acousto-optical deflectors or Nipkow discs, but a drawback is that the scanning pattern is not a linear but rather a sinusoidal function of time. This puts additional constraints on the hardware necessary to read-in the image data flow, one of which is the generation of a pixel clock that varies in frequency with the position of the pixel on the scanned line. We describe a practical solution to obtain a variable pixel clock add-on that is easy to build and is easy to integrate into a custom-built LSM based on resonant scanning technology. In addition, we discuss some important hardware and software design aspects that simplify the construction of a resonant scanning-based LSM for high-speed, high-resolution imaging. Finally, we demonstrate that the microscope can be used to resolve calcium puffs triggered by photolytically increasing the intracellular concentration of inositol trisphosphate.

Complex oscillations and waves of calcium in pancreatic acinar cells

We perform a bifurcation analysis of a model of Ca 2+ wave propagation in the basal region of pancreatic acinar cells. The model we consider was first presented in Sneyd et al. [J. Sneyd, K. Tsaneva-Atanasova, J.I.E. Bruce, S.V. Straub, D.R. Giovannucci, D.I. Yule, A model of calcium waves in pancreatic and parotid acinar cells, Biophys. J. 85 (2003) 1392–1405], where a partial bifurcation analysis was given of the model in the absence of diffusion. We obtain more complete information about bifurcations of the diffusionless model via numerical studies, then analyse the spatially extended model by numerical investigation of the travelling wave equations and direct numerical solution of the model equations. We find solitary waves in the model equations arising from homoclinic bifurcations in the travelling wave equations. The solitary waves exist and appear to be stable for a significant interval of the primary bifurcation parameter (i.e., the concentration of inositol trisphosphate) but are eventually replaced by irregular spatio-temporal behaviour. The homoclinic bifurcations are related to a number of complicated mathematical structures in the travelling wave equations, including an anomalous homoclinic-Hopf bifurcation, heteroclinic bifurcations between an equilibrium and a periodic orbit, and homoclinic bifurcations of periodic orbits.

Intercellular Ca2+ waves induce temporally and spatially distinct intracellular Ca2+ oscillations in glia

Mechanically induced intercellular Ca(2+) waves propagated for approximately 300 microm in primary glial cultures. Following the wave propagation, 34% of the cells displayed Ca(2+) oscillations in a zone 60-120 microm from the stimulated cell. The initiation, frequency, and duration of these Ca(2+) oscillations were dependent on the cells' distance from the wave origin but were not dependent on the cell type nor on the magnitude of the Ca(2+) wave. When an individual cell propagated two sequential intercellular Ca(2+) waves originating from different sites, the characteristics of the Ca(2+) oscillations initiated by each wave were determined by the distance of the cell from the origin of each wave. Each Ca(2+) oscillation commonly occurred as an intracellular Ca(2+) wave that was initiated from a specific site within the cell. The position of the initiation site and the direction of the intracellular Ca(2+) wave were independent of the orientation of the initial intercellular Ca(2+) wave. Because initiation and frequency of Ca(2+) oscillations are dependent on the intracellular inositol trisphosphate concentration ([IP(3)](i)), we propose that the zone of cells displaying Ca(2+) oscillations is determined by an intercellular gradient of [IP(3)](i), established by the diffusion of IP(3) through gap junctions during the propagation of the intercellular Ca(2+) wave. Exposure to acetylcholine, a muscarinic agonist that initiates IP(3) production, shifted the zone of oscillating cells about 45 microm farther away from the origin of the mechanically induced wave. These findings indicate that a glial syncytium can resolve information provided by a local Ca(2+) wave into a distinct spatial and temporal pattern of Ca(2+) oscillations.

Prostaglandin E 2 in the salivary glands of the female tick, Amblyomma americanum (L.): calcium mobilization and exocytosis

A cholera toxin-sensitive, prostaglandin E 2 (PGE 2) specific receptor has been identified in the plasma membrane fraction of tick salivary glands. In the present study, we report that stimulation of dispersed salivary glands of the lone star tick Amblyomma americanum (L.) with 1 nM to 10 μM PGE 2 increased the intracellular concentration of inositol trisphosphate (IP 3) in a dose-dependent manner. Incubation of dispersed tissue with 1 nM to 10 μM PGE 2 also stimulated release of 45Ca 2+ from preloaded tissue. PGE 2 (10 μM) did not stimulate an influx of 45Ca 2+. Therefore, the PGE 2 receptor in the salivary glands appears to activate a phosphoinositide phospholipase C signalling pathway to increase formation of intracellular IP 3 and, thus, mobilize Ca 2+ from intracellular stores. Incubation of dispersed salivary glands with 1 nM to 1 μM PGE 2 stimulated secretion of anticoagulant protein, but not at <1 nM or >1 μM PGE 2. In addition, the mammalian PGE 2 EP1 receptor antagonist AH-6809 affected secretion of anticoagulant by dispersed salivary gland tissue at a low concentration supporting the hypothesis that the PGE 2 receptor in tick salivary glands is EP1-like. We propose that a major function for PGE 2 in tick salivary glands is to mobilize Ca 2+ and stimulate secretion (exocytosis) of bioactive proteins into the tick's saliva during feeding.

Cuticular hydrocarbons control behavioural phase transition in Schistocerca gregaria nymphs and elicit biochemical responses in antennae

Cuticular lipid extracts have been shown to induce gregarious phase-related behaviour in Schistocerca gregaria solitarious nymphs. Analysis of various fractions of the cuticular lipids reveals that the behavioural response is specific to the hydrocarbon fraction. On exposure to cuticular hydocarbons, antennal preparations from crowded S. gregaria nymphs and adults generate a rapid and transient increase in the concentration of inositol trisphosphate (IP 3), whereas the level of cAMP is not affected. Antennal preparations from locust nymphs are more responsive to the hydrocarbon fraction than are preparations from adults. IP 3 generation is dose-dependent and species-specific. The notion that the cuticular hydrocarbons may interact with membrane receptors of antennal sensory cells is supported by the observation that hydrocarbon-induced IP 3 formation is significantly impaired in the presence of GDP-β-S, an inhibitor of trimeric G-protein function. These findings confirm the view that components of cuticular hydrocarbons function in locusts as contact pheromones, specifically inducing gregarious phase behaviour, and that they initially act via induction of IP 3

The Effects of Inositol 1,4,5-Trisphosphate (InsP3) Analogues on the Transient Kinetics of Ca2+ Release from Cerebellar Microsomes: InsP3 ANALOGUES ACT AS PARTIAL AGONISTS

An investigation of the effects of a number of inositol trisphosphate analogues on the transient kinetics of Ca2+ release from cerebellar microsomes was undertaken. All the analogues investigated could release the total Ca2+ content of the inositol 1, 4,5-trisphosphate (Ins(1,4,5)P3) mobilizable Ca2+ store; however, their potencies were substantially reduced compared to Ins(1,4,5)P3. The concentration required to induce half-maximal Ca2+ mobilization was 0.14 microM for Ins(1,4,5)P3, 1.8 microM for 3-deoxyinositol 1,4, 5-trisphosphate (3-deoxyInsP3), 1.0 microM for 2,3-dideoxyinositol 1, 4,5-trisphosphate (2,3-dideoxyInsP3), 24 microM for 2,3, 6-trideoxyinositol 1,4,5-trisphopshate (2,3,6-trideoxyInsP3), and 2.9 microM for inositol 2,4,5-trisphosphate (Ins(2,4,5)P3). In all cases and for all concentrations tested, the inositol trisphosphate analogues induced biphasic transient release of Ca2+, which could fit to a biexponential equation assuming two independent processes. The rate constants calculated for the release process were much larger for Ins(1,4,5)P3 than the other inositol trisphosphates (the fast phase rate constant varying from 0.3 to 1.6 s-1 and the slow phase from 0.01-0.5 s-1, at concentrations between 0.03 and 20 microM Ins(1,4,5)P3). The rate constants for all other inositol trisphosphates did not appear to exceed 0.4 s-1 for the fast phase and 0.1 s-1 for the slow phase at their highest concentrations tested. The maximum amplitudes for Ca2+ release by the two phases appeared to be similar for all inositol trisphosphates (approximately 45% for the fast phase and approximately 55% for the slow phase). On comparing the rate constants for Ca2+ release at inositol trisphosphate concentrations for the analogues which all induced the same extent of Ca2+ release, it was apparent that the rates of release were independent of the extent of Ca2+ release. As the extent of Ca2+ release can be related to degree of occupancy of the binding sites, it is evident that different analogues which occupy the binding site of the receptor to the same extent can induce Ca2+ to be released at different rates. We explain this conclusion in terms of partial agonism where inositol phosphates can induce two (or more) occupied states of the channel.

Radiolabeled ligands specific for the G protein-coupled state of neurotensin receptors.

Radiolabeled analogues of neuromedin N have been prepared by acylation of the alpha, epsilon 1, and epsilon 2 amino groups of [Lys2]neuromedin N (Lys-Lys-Pro-Tyr-Ile-Leu) either with the 125l-labeled Bolton-Hunter reagent or with N-succinimidyl[2,3-3H]propionate. The binding properties of the purified analogues toward newborn mouse brain homogenate or toward membranes of cells transitorily (COS) or permanently (AA1) transfected with the cloned rat brain neurotensin receptor cDNA were evaluated and compared with those of radiolabeled neurotensin. The alpha-modified analogue of [Lys2]neuromedin N behaves exactly like neurotensin in these binding experiments, whereas the epsilon 1- and epsilon 2-modified analogues selectively recognize the fraction of neurotensin binding sites that is sensitive to GTP gamma S. The proportion of neurotensin receptors coupled to GTP binding proteins is approximately 50% in membranes of newborn mouse brain or of AA1 cells that respond to neurotensin by an increase of the intracellular inositol trisphosphate concentration. By contrast, membranes of transitorily transfected COS cells that do not respond to neurotensin exhibit very low levels of GTP-sensitive receptors labeled with the epsilon 1- or epsilon 2-modified analogues. These radiolabeled peptides offer new tools to selectively detect active neurotensin receptors.

Protein kinase C activation inhibits receptor-evoked inositol trisphosphate formation and induction of cytosolic calcium oscillations by decreasing the affinity-state of the cholecystokinin receptor in pancreatic acinar cells

Digital-imaging microscopy of Fura-2-loaded pancreatic acinar cells revealed that the C-terminal octapeptide of cholecystokinin (CCK 8) dose-dependently recruited 94% of freshly isolated acinar cells in terms of receptor-evoked Ca 2+ mobilization. Maximal and half-maximal cell-recruitment were reached with 0.1 nM and 16.8 pM CCK 8, respectively. The upstroke of the dose-recruitment curve consisted of cells displaying oscillatory changes in free cytosolic Ca 2+ concentration ([Ca 2+] i). After having reached its maximum, the percentage oscillating cells dose-dependently decreased upon further increasing of the CCK 8 concentration. Pretreatment of the acinar cells with 0.1 μM TPA caused a rightward shift of the dose-recruitment curve but did not change the maximal effect of CCK 8 on the recruitment of oscillating cells. Half-maximal recruitment was obtained with 287 pM CCK 8. This observation demonstrates that high levels of protein kinase C activation do not inhibit Ca 2+ oscillations at a level downstream to receptor activation. Moreover, this observation demonstrates that protein kinase C-mediated inhibition of Ca 2+ oscillations evoked by submaximal CCK 8 concentrations occurs at the receptor level, converting it from a high-affinity state into a low-affinity state. This conclusion is supported by the observation that TPA completely inhibited the recruitment of acinar cells in response to the high-affinity receptor agonist JMV-180. The inhibitory action of TPA on CCK 8-evoked cell-recruitment was paralleled by an inhibitory effect of the phorbol ester on the CCK 8-evoked peak increase in average inositol trisphosphate concentration in a population of acinar cells. This observation indicates that low concentrations of CCK8 interact with the high-affinity CCK receptor to increase [Ca 2+] i through the intermediation of inositol trisphosphate.

Cyclic 3′5′ adenosine monophosphate mediates dopamine-enhanced hindgut contractions in the crayfish, Procambarus clarkii

Abstract The present study examined the hypothesis that cyclic adenosine 3′5′ monophosphate (cAMP) serves as a second messenger in mediating dopamine-enhanced contractions in the hindgut of the crayfish Procambarus clarkii . Dopamine increased cAMP levels in isolated hindguts in a dose-dependent manner, with a threshold between 10 −8 and 10 −7 M. The concentration of inositol trisphosphate (IP 3 ) was not increased significantly following a 5 min exposure to 10 −4 M dopamine. Forskolin and IBMX, known to increase cAMP levels, mimicked the physiological actions of dopamine by enhancing spontaneous hindgut contractions. IBMX, which is known to inhibit the hydrolysis of cAMP, potentiated the effect of a low concentration of dopamine on hindgut contractions. These data support the hypothesis that the enhancement of hindgut contractions elicited by dopamine is at least partly mediated through an elevation of cAMP levels.

The initiation of a calcium signal in Xenopus oocytes

Application of acetylcholine to Xenopus oocytes evoked increases in the cytosolic free calcium ion concentration ([Ca 2+] i) after latencies of up to several seconds depending on the agonist dose. Higher acetylcholine concentrations evoked responses with larger amplitudes and shorter latencies. The latencies of responses to acetylcholine could be increased by application of caffeine, injection of calcium buffers or depletion of intracellular calcium stores. Acute inhibition of endoplasmic reticulum calcium pumps without substantial reduction of the calcium store content (by application of thapsigargin shortly before agonist stimulation) reduced the latencies of responses to acetylcholine. A schematic and mathematical model are presented to show a possible mechanism by which a calcium signal is initiated following a latent period after the elevation of the inositol trisphosphate concentration. During the latent period, calcium is slowly released from the intracellular stores. The released calcium is rapidly buffered by cytosolic calcium-binding proteins and some is resequestered into the stores by calcium pumps. The [Ca 2+] i changes very little until the buffering is locally saturated. The [Ca 2+] i then rises above a threshold concentration which evokes an explosive release of calcium due to positive feedback by calcium on the inositol trisphosphate receptor.

Modulation of the intracellular Ca2+ and inositol trisphosphate concentrations in murine T lymphocytes by the glycosylphosphatidylinositol-anchored protein sgp-60.

Stimulation of T lymphocytes via the TCR/CD3 complex initiates a series of intracellular biochemical events. Among the earliest cellular responses are the stimulation of the turnover of phosphatidylinositol and an increase in the intracellular Ca2+ concentration. The significance of these second messengers for distal cellular responses such as lymphokine production or cell proliferation is not understood. We have previously shown that hamster mAb to the murine glycosylphosphatidylinositol-anchored protein sgp-60 can inhibit IL-2 production, IL-2R expression, and cell proliferation, events normally observed after stimulation of T cells with an antibody to the TCR/CD3 complex or with the lectin Con A. We now show that the anti-sgp-60 mAb inhibits the activation-induced increase in intracellular Ca2+ concentration. Additional analysis demonstrates that the mAb interferes with the release of Ca2+ from intracellular stores and with the generation of inositol 1,4,5-trisphosphate. Our findings suggest a role for this glycosylphosphatidylinositol-anchored protein in the generation of second messengers in signal transduction through the TCR/CD3 complex in murine T lymphocytes.

Olfactory signalling in antennal receptor neurones of the locust ( Locusta migratoria)

The electrical properties of isolated antennal neurones from Locusta migratoria were investigated using patch clamp techniques. The neurones displayed a resting potential of −26±11 mV ( n=38) and an input resistance between 1–6 GΩ. Upon application of depolarizing voltage steps a non-inactivating non-specific inward current and a calcium-dependent outward potassium current were identified. Some neurones responded to stimulation by the grass odour hexenoic acid (1–100 μM) with an increase in ion channel activity in cell-attached recordings. This channel was identified as a calcium-activated potassium channel belonging to the maxi-K +-channel types. Odour-stimulation of antennal tissue and antennal cells using a fast quency device leads to a rapid generation of inositol 1,4,5-trisphosphate, supporting the idea that this substance acts as second messenger in insect olfaction. The odour-induced increase in inositol trisphosphate concentration may initiate a rise in intracellular calcium controlling the activity of calcium-dependent ion channels.

Neurotransmission in the urinary bladder of rabbits and guinea pigs.

Alpha, beta-Methyleneadenosine 5'-triphosphate (alpha, beta-mATP) produced transient contraction of strips of bladder taken from rabbits or guinea pigs, and mechanical responses to field stimulation at 5-100 Hz were reduced by this drug by 5-20%. Atropine reduced responses by approximately 50%, and both drugs together by 80-95%. In double sucrose gap experiments on the rabbit bladder, alpha, beta-mATP selectively reduced but did not abolish an initial excitatory junction potential (ejp), and atropine selectively abolished a late depolarization. In the guinea pig, a single ejp was partially inhibited by either alpha,beta-mATP or atropine. Residual responses were further reduced by tetrodotoxin in both species. The initial ejp and late depolarization in the rabbit were reduced in parallel by hemicholinium over 2 h, suggesting that release of acetylcholine (ACh) and the second transmitter by nerves may be coupled. ACh but not ATP produced an increase in intracellular concentration of inositol trisphosphate in dispersed smooth muscle cells from the rabbit bladder; ATP but not carbachol produced a small transient current across the cell membrane in this species. It is concluded that ACh mobilizes intracellular Ca2+ for contraction, whereas the effect of ATP is dependent on extracellular Ca2+.

Alterations in vasopressin and angiotensin II receptors and responses during culture of rat liver cells

Vasopressin and angiotensin II binding and responses were studied in hepatocytes in primary culture for 4 h and 24 h. After 24 h of culture, angiotensin II was completely ineffective in elevating cytosolic [Ca 2+], whereas the maximum [Ca 2+] response to vasopressin was decreased by 66% and the sensitivity to the hormone was decreased approx. 20-fold compared with values after 4 h of culture. The dissociation constant ( K D) for vasopressin binding to the cells was not significantly changed during 24 h of culture, but the B max was decreased by 63% compared with 4 h of culture. There was also no change in the K D for angiotensin II binding from 4 h to 24 h, but the B max was decreased by 90%. After 24 h of culture, there was no change in the plasma membrane concentration of phosphatidylinositol 4,5-bisphosphate or in the basal cell concentration of inositol trisphosphate. However, the trisphosphate did not increase with 100 nM angiotensin II and the response to 100 nM vasopressin was reduced by 66% compared with that at 4 h. The effect of guanosine 5′-(3- O-thiol) triphosphate on the polyphosphoinositide phospholipase C activity of liver cell plasma membranes was also measured. There was no decrease in the degree of stimulation of the phospholipase by this nucleotide after 24 h of culture. It is concluded that the loss of vasopressin and angiotensin II responses in cultured liver cells is due in part to changes in receptors and also in their coupling to a guanine nucleotide binding protein.

Rapid activation of alternative second messenger pathways in olfactory cilia from rats by different odorants.

The molecular mechanisms mediating the chemo-electrical signal transduction in olfactory receptor cells are still elusive. In this study odor induced formation of second messengers in rat olfactory cilia was monitored in a subsecond time range using a rapid kinetic device. Application of micromolar concentration of citralva induced a rapid, transient elevation of the cyclic adenosine monophosphate level, whereas the concentration of inositol trisphosphate was not affected. In contrast, pyrazine caused a rise in the concentration of inositol trisphosphate, not affecting the level of cyclic adenosine monophosphate. Analysis of the kinetic parameter for the odorant induced reaction indicated that apparently two systems are operating simultaneously. The activating effects of odorants appear to be mediated via different G-proteins. Thus, at least two different second messenger pathways appear to be involved in olfactory signal transduction.