Three multispectral configurations of a snapshot kaleidoscope-based camera in long wavelength infrared spectral band

In the field of spectral imaging, numerous instruments use scanning-based technologies. However, the temporal dimension of these systems, whether to scan the spectrum or scan the scene, can be an issue for some applications. This is particularly the case when trying to observe and identify rapid temporal variations in a fixed scene or detecting objects of interest when moving. In this case, it is suitable to observe the desired spectral information of the scene simultaneously, and so-called snapshot systems have been thus investigated. In this paper, we study the ability of a kaleidoscope-based multiview camera to acquire multispectral information in the long wavelength infrared. Several strategies and technologies will be compared to add the spectral function inside the different blocks of a kaleidoscope-based camera: the front lens, the kaleidoscope, or the reimaging lens. The studied camera uses an uncooled infrared detector and thus must deal with the issue of having a large aperture.

Kaleidoscope-based multi-view infrared system

Multi-view snapshot systems are used for a wide range of applications in all the spectral ranges. In this Letter, we present the study and the realization of an optical system using a kaleidoscope in the long wavelength infrared (LWIR), compatible with uncooled infrared detectors such as microbolometers. The optical system has a high numerical aperture and a wide field of view, and it uses a single focal plane array. Here, we establish the advantages of this technology on other design strategies and its design rules for every subset of the optical architecture, and we present the results of a first demonstrator.

Compact multichannel infrared camera integrated in an operational detector dewar cooler assembly

We present an ultracompact infrared cryogenic camera integrated inside a standard Sofradir's detector dewar cooler assembly (DDCA) whose field of view is equal to 120°. The multichannel optical architecture produces four nonredundant images on a single SCORPIO detector with a pixel pitch of 15 μm. This ultraminiaturized optical system brings a very low additional optical and mechanical mass to be cooled in the DDCA: the cool-down time is comparable to an equivalent DDCA without an imagery function. Limiting the number of channels is necessary to keep the highest number of resolved points in the final image. However, optical tolerances lead to irregular shifts between the channels. This paper discusses the limits of multichannel architectures. With an image-processing algorithm, the four images produced by the camera are combined to process a single full-resolution image with an equivalent sampling pitch equal to 7.5 μm. Experimental measurements on the modulation transfer function and noise equivalent temperature difference show that this camera achieves good optical performance.

Reduction of material mass of optical component in cryogenic camera by using high-order Fresnel lens on a thin germanium substrate

We designed a compact infrared cryogenic camera using only one lens mounted inside the detector area. In the field of cooled infrared imaging systems, the maximal detector area is determined by the dewar. It is generally a sealed and cooled environment dedicated to the infrared quantum detector. By integrating an optical function inside it, we improve the compactness of the camera as well as its performances. The originality of our approach is to use a thin integrated optics which is a high quality Fresnel lens on a thin germanium substrate. The aim is to reduce the additional mass of the optical part integrated inside the dewar to obtain almost the same cool down time as a conventional dewar with no imaging function. A prototype has been made and its characterization has been carried out.

Extra-thin infrared camera for low-cost surveillance applications

We designed a cheap broadband uncooled microimager operating in the long-wavelength infrared range using only one lens at a minimal cost for the manufacturing process. The approach is based on thin optics where the device volume is small and therefore inexpensive materials can be used because some absorption can be tolerated. We have used a Fresnel lens on a thin silicon substrate. Up to now, Fresnel lenses have not been used for broadband imaging because of their chromatic properties. However, working in a relatively high diffraction order can significantly reduce chromatism. A prototype has been made for short range or indoor low-cost surveillance applications like people counting, and experimental images are presented.

Three-dimensional imaging using continuously self-imaging gratings

In this Letter, we propose a method to perform 3D imaging with a simple and robust imaging system only composed of a continuously self-imaging grating (CSIG) and a matrix detector. With a CSIG, the intensity pattern generated by an object source is periodic and propagation invariant, apart from a dilatation factor that depends on the distance of the object. We demonstrate, theoretically and experimentally, how to exploit this property to analyze a scene in three dimensions. Such an imaging system can be used, for example, for tomographic applications.

Regularized image reconstruction for continuously self-imaging gratings

In this paper, we demonstrate two image reconstruction schemes for continuously self-imaging gratings (CSIGs). CSIGs are diffractive optical elements that generate a depth-invariant propagation pattern and sample objects with a sparse spatial frequency spectrum. To compensate for the sparse sampling, we apply two methods with different regularizations for CSIG imaging. The first method employs continuity of the spatial frequency spectrum, and the second one uses sparsity of the intensity pattern. The two methods are demonstrated with simulations and experiments.

Relevance of continuously self-imaging gratings for noise robust imagery

We have designed miniaturized, simple, and robust cameras composed of a single diffractive optical element (DOE) that generates a continuously self-imaging (CSI) beam. Two different DOEs are explored: the J0 Bessel transmittance, characterized by a continuous optical transfer function (OTF) and the CSI grating (CSIG), characterized by a sparse OTF. In this Letter, we will analyze the properties of both DOEs in terms of radiometric performances. We will demonstrate that the noise robustness is enhanced for a CSIG, thanks to the sparsity of its OTF. A camera using this DOE has been made and experimental images are presented to illustrate the noise robustness.

Angular acceptance analysis of an infrared focal plane array with a built-in stationary Fourier transform spectrometer

Stationary Fourier transform spectrometry is an interesting concept for building reliable field or embedded spectroradiometers, especially for the mid- and far- IR. Here, a very compact configuration of a cryogenic stationary Fourier transform IR (FTIR) spectrometer is investigated, where the interferometer is directly integrated in the focal plane array (FPA). We present a theoretical analysis to explain and describe the fringe formation inside the FTIR-FPA structure when illuminated by an extended source positioned at a finite distance from the detection plane. The results are then exploited to propose a simple front lens design compatible with a handheld package.

Relevance of an inverse problem approach to overcome cut-off wavenumbers disparities in infrared stationary Fourier transform spectrometers

One of the major limitations to the use of infrared focal plane arrays (IRFPAs) in stationary Fourier transform spectrometers (FTSs) comes from the spatial inhomogeneities of the pixel responses, where the inhomogeneities of the cut-off wavenumbers of the pixels can prevail. The hypothesis commonly assumed for FTSs that all the pixels are equivalent is thus inaccurate and results in a degradation of the estimated spectrum, even far from the cut-off wavenumbers. However, if the individual spectral responses of the pixels are measured beforehand, this a priori information can be used in the inversion process to produce reliable spectra. Thus, spatial inhomogeneities are not an obstacle for the use of infrared stationary FTS. This result is illustrated in this paper by numerical simulations, based on a realistic description of an IRFPA.

Compact infrared cryogenic wafer-level camera: design and experimental validation

We present a compact infrared cryogenic multichannel camera with a wide field of view equal to 120°. By merging the optics with the detector, the concept is compatible with both cryogenic constraints and wafer-level fabrication. The design strategy of such a camera is described, as well as its fabrication and integration process. Its characterization has been carried out in terms of the modulation transfer function and the noise equivalent temperature difference (NETD). The optical system is limited by the diffraction. By cooling the optics, we achieve a very low NETD equal to 15 mK compared with traditional infrared cameras. A postprocessing algorithm that aims at reconstructing a well-sampled image from the set of undersampled raw subimages produced by the camera is proposed and validated on experimental images.

Optimal conditions for using the binary approximation of continuously self-imaging gratings

Diffractive Optical Elements (DOE), that generate a propagation-invariant transverse intensity pattern, can be used for metrology and imaging application because they provide a very wide depth of focus. However, exact implementation of such DOE is not easy, so we generally code the transmittance by a binary approximation. In this paper, we will study the influence of the binary approximation of Continuously Self-Imaging Gratings (CSIG) on the propagated intensity pattern, for amplitude or phase coding. We will thus demonstrate that under specific conditions, parasitic effects due to the binarization disappear and we retrieve the theoretical non-diffracting property of CSIG's.

Inverse problem approaches for stationary Fourier transform spectrometers

A design of a miniaturized stationary Fourier transform IR spectrometer has been developed that produces a two-dimensional interferogram. The latter is disturbed by effects like parasitic interferences or disparities in the cutoff wavelength of the pixels. Thus, a simple Fourier transform cannot be used to estimate the spectrum of the scene. However, as these defects are deterministic, they can be measured and taken into account by inversion methods. A regularization term can also be added. The first experimental results prove the efficiency of this processing methodology.

Quadriwave lateral shearing interferometry in an achromatic and continuously self-imaging regime for future x-ray phase imaging

We present in this Letter a type of quadriwave lateral shearing interferometer for x-ray phase imaging. This device is based on a phase chessboard, and we take advantage of the large spectrum of the source to produce interferograms with a propagation-invariant contrast. Such a grating has been created for hard x-ray interferometry and experimentally tested on a synchrotron beamline at Soleil.

Random phase mask in a filamentation regime: application to the localization of point sources

We present a optical system with an extended point-spread function (PSF) for the localization of point sources in the visible and IR spectral ranges with a subpixel precision. This compact system involves a random phase mask (RPM) as its unique component. It exhibits original properties, because this RPM is used in a particular regime, called the "filamentation regime," before the speckle region. The localization is performed by calculating the phase correlation between the PSF and the image obtained under off-axis illumination. Numerical simulations are presented to assess the basic optical properties of this RPM in the filamentation regime.

Design strategies to simplify and miniaturize imaging systems

We present the range of optical architectures for imaging systems based on a single optical component, an aperture stop, and a detector. Thanks to the formalism of third-order Seidel aberrations, several strategies of simplification and miniaturization of optical systems are examined. Figures of merit are also introduced to assess the basic optical properties and performance capabilities of such systems; by this way, we show the necessary trade-off between simplicity, miniaturization, and optical performance.

Modulation transfer function measurement of a multichannel optical system

We present a new method to measure the modulation transfer function (MTF) beyond the Nyquist frequency of a multichannel imaging system for which all the channels have parallel optical axes. Such a multichannel optical system produces a set of undersampled subimages. If the subimages contain nonredundant information, high spatial frequencies are folded between low spatial frequencies, leading to the possible extraction of frequencies higher than the Nyquist frequency. The measurement of the MTF of the multichannel system leads to the estimation of the resolution enhancement of the final image that can be obtained by applying a postprocessing algorithm to the collection of undersampled subimages. Experimental images are presented to validate this method.

Demonstration of an infrared microcamera inspired by Xenos peckii vision

We present an original and compact optical system inspired by the unusual eyes of a Strepsipteran insect called Xenos peckii. It is designed for a field of view of 30 degrees and is composed of multiple telescopes. An array of prisms of various angles is placed in front of these telescopes in order to set a different field of view for each channel. This type of camera operates in the [3-5 microm] spectral bandwidth and is entirely integrated in a Dewar in order to maximize its compactness. Experimental images are presented to validate this design.

Compact infrared pinhole fisheye for wide field applications

The performances of a compact infrared optical system using advanced pinhole optics for wide field applications are given. This concept is adapted from the classical Tisse design in order to fit with infrared issues. Despite a low light gathering efficiency and a low resolution in comparison with classical lenses, pinhole imagery provides a long depth of field and a wide angular field of view. Moreover, by using a simple lens that compresses the field of view, the angular acceptance of this pinhole camera can be drastically widened to a value around 180°. This infrared compact system is named pinhole fisheye since it is based on the field lens of a classical fisheye system.

Infrared focal plane array with a built-in stationary Fourier-transform spectrometer: basic concepts

A novel configuration of stationary Fourier transform infrared (FTIR) spectrometer is presented. Contrary to classic configurations, the interferometer is directly integrated in the focal plane array (FPA) during its process of fabrication. A first, to the best of our knowledge, demonstration of the spectrometric function has been achieved departing from a well-known structure of an HgCdTe photodetector. We show that the obtained FTIR-FPA can be described by intrinsic parameters such as an optical path difference and a so-called spectrometric efficiency. First experimental results are presented.

Holistic characterization of complex transmittances generated by infrared sub-wavelength gratings

We present a characterization technique of wide-area subwavelength structures. The optical bench is based on lateral shearing interferometry, which allows an accurate complex transmittance (phase and amplitude) measurement. The experimental validation is made in the long-wavelength infrared domain; more precisely we work in the integrated 8-9 microm spectral range. Measurements of the transmitted amplitude and phase shift reveal a good agreement with respectively experimental results based on Fourier Transform infrared spectrometry, and theoretical simulations.

Demonstration of image-zooming capability for diffractive axicons

Diffractive axicons are optical components producing achromatic nondiffracting beams. They thus produce a focal line rather than a focal point for classical lenses. This gives the interesting property of a long focal depth. We show that this property can be used to design a simple imaging system with a linear variable zoom by using and translating a diffractive axicon as the only optical component.

Nonparaxial analysis of continuous self-imaging gratings in oblique illumination

Tolerance in angles of continuously self-imaging gratings (CSIGs) is explored. The degradation in angle of the shape of the point-spread function is theoretically investigated and illustrated by simulations and experiments. The formalism presented is inspired by the one used for classical lenses and can be easily generalized to diffraction gratings. It turns out that well-designed CSIGs could be used for scanning optical systems requiring a large field of view.

Single-scan extraction of two-dimensional parameters of infrared focal plane arrays utilizing a Fourier-transform spectrometer

We present what is believed to be a novel experimental method to measure the technological parameters (spectral response and quantum yield) of an infrared focal plane array. This method makes original use of a Fourier transform spectrometer, which allows us to simultaneously extract the spectral performances of all pixels from one single set of measurements. The methodology used and the principle of the experimental setup are detailed. A Fourier analysis is shown to provide various optogeometrical information on the detector microstructure. A demonstrator based on the HgCdTe technology was designed, and satisfactory experimental results were obtained.

Two-color multi-wave lateral shearing interferometry for segmented wave-front measurements

The possibility to measure segmented wave-front thanks to lateral shearing interferometry using diffraction grating is presented and analyzed. Aside from the response of such technique, the dynamic range is evaluated and shown to be limited. To greatly extend this one, a new method based on the use of two colors, not necessarily monochromatic, combined with an innovative Fourier treatment, is proposed. The two-color proposed in this paper is a high dynamic and low sensitivity technique; it can be completed by a one-color analysis, with low dynamics and high sensitivity, to reach high precision measurements. The ability of this method to measure Keck-like wave-front is demonstrated thanks to a computational analysis. Finally, a first experimental measurement of an etched substrate by using a quadri-wave lateral shearing interferometer is detailed.

In situ optical testing of infrared lenses for high-performance cameras

We propose to evaluate infrared lenses with a dedicated analyzer having the same mechanical interface as the usual cameras. The proposed analysis is based on a wavefront measurement and allows a diagnostic of possible internal defects of the analyzed lens. The infrared lens analyzer described is constituted with a quadriwave lateral shearing interferometer and works with a blackbody light. We describe the response of this interferometer and an innovative method to obtain the wavefront under test. We finally present the experimental analysis of long-wavelength infrared lenses and the particular case of a modified lens that generates a large spherical aberration.

Wollaston prism-like devices based on blazed dielectric subwavelength gratings

A Wollaston prism-like binary dielectric grating is presented and analyzed. It behaves like a transmission grating, differentially and symmetrically blazed for the two crossed polarization states, TE and TM. The phase profile is obtained by means of subwavelength structures etched in a high optical index isotropic dielectric medium (gallium arsenide, for instance). The performance of the device is illustrated by numerical examples and sketched in terms of spectral bandwidth and of extinction ratio. Some practical issues related to the fabrication are discussed.

Wave-front reconstruction from multidirectional phase derivatives generated by multilateral shearing interferometers

To increase the accuracy of wave-front evaluation, we propose to exploit the natural capability of multiple lateral shearing interferometers to measure simultaneously more than two orthogonal phase derivatives. We also describe a method, based on Fourier-transform analysis, that uses this multiple information to reconstruct the wave-front under study.

Sharpness limitations in the projection of thin lines by use of the Talbot experiment

Studying the limitations of sharpness in self-images of the Talbot effect leads us to abandon the use of the paraxial assumption. In this respect, we will clarify the self-image concept and show experimentally and theoretically the influence of "nonparaxial effects" on the self-image. The boundary between paraxial and nonparaxial scalar theory is also clarified in this context. The Rayleigh criterion in aberration diffraction theory is adapted for explicit estimations of this boundary and the maximum sharpness of lines projected by use of the Talbot effect.

Talbot experiment re-examined: study of the chromatic regime and application to spectrometry

The original Talbot experiment in white light has been reconstituted, using an amplitude grating made of thin slits and a colour CCD camera and a model has been developed to describe the field diffracted by the grating illuminated in polychromatic light with a known spectral density. Above the historical interest of this study, the possibility of applying this effect to make spectral measurements is explored and a new concept of Talbot spectrometer is proposed.

Generation of achromatic and propagation-invariant spot arrays by use of continuously self-imaging gratings

A particular class of Montgomery's self-imaging objects that we call continuously self-imaging gratings (CSIG's) is introduced. When they are illuminated by a plane wave, these objects produce a field whose intensity profile is a propagation- and wavelength-invariant biperiodic array of bright spots. The mathematical construction of these objects and their intrinsic properties are described. On a practical level, CSIG's are compact and achromatic nondiffracting array generators. We show that a good CSIG approximation can be realized by a two-level phase grating that is experimentally tested.

Extended hartmann test based on the pseudoguiding property of a hartmann mask completed by a phase chessboard

We propose to add a specific phase chessboard to the classical Hartmann mask used for wave-front sensing. By doing this we obtain a pseudoguiding of the energy issuing from this mask, allowing for an increase in the sensitivity of the Hartmann test. This property is illustrated by experiment, and a comparison between classical and new Hartmanngrams is presented.

Modulation transfer function measurement of an infrared focal plane array by use of the self-imaging property of a canted periodic target

We present a new technique for measuring the modulation transfer function (MTF) of a focal plane array (FPA). The main idea is to project a periodic pattern of thin lines that are canted with respect to the sensor's columns. Practically, one aims the projection by using the self-imaging property of a periodic target. The technique, called the canted periodic target test, has been validated experimentally on a specific infrared FPA, leading to MTF evaluation to as great as five times the Nyquist frequency.

Cytosolic Ca2+ of excitable pituitary cells at resting potentials is controlled by steady state Ca2+ currents sensitive to dihydropyridines

Different elements of voltage-gated Ca2+ influx and their role for cytosolic-free Ca2+, [Ca2+]i, were studied in cells of the pituitary line GH3B6. Single cell monitoring of [Ca2+]i with the fluorescent probe indo-1, as well as fast on-line ratio [Ca2+]i imaging with fura-2, were combined with electrophysiological recordings using the perforated patch configuration of the patch clamp technique. [Ca2+]i signals are generated by Ca2+ influx both during action potentials and in between. Steady state Ca2+ influx at resting potentials (-60 to -40 mV) was voltage-gated and sensitive to the dihydropyridine antagonist PN 200-110. Ca2+ influx could be demonstrated in physiological conditions as inward Ca2+ currents of maximally 10 pA, which were triggered when stepping up the holding voltage beyond a narrow threshold around -50 mV. Inward currents were well correlated with [Ca2+]i elevations (R = -0.8; p < 0.001). It is concluded that dihydropyridine-sensitive, low threshold voltage-gated steady state Ca2+ currents, which may be tonically activated at resting potentials, provide for [Ca2+]i signaling in excitable endocrine cells in a mode that parallels the modulation of Ca2+ influx during action potentials.

Effects of two neuronal antidiuretic molecules, neuroparsin and 5-hydroxytryptamine, on cytosolic free calcium monitored with indo-1 in epithelial and muscular cells of the African locust rectum

Using the probe indo-1 in a microspectrofluorimetric study, it was demonstrated that the locust antidiuretic neurohormone, neuroparsin, enhanced cytosolic free Ca2+ concentrations, measured as percentages of the ratio F405/F480 (R), in epithelial cells of the African locust rectum. 5-hydroxytryptamine, whose antidiuretic effect was previously established, enhanced R in longitudinal muscular cells, and was able to increase R slightly in epithelial cells. The possibility of reciprocal Ca2+ movements between muscular and epithelial cells is discussed. Both of the neuronal molecules, which act via distinct transduction pathways (phosphoinositide turnover for neuroparsin, and Ca(2+)-dependent adenylate cyclase for 5-hydroxytryptamine), stimulated an increase in R by causing Ca2+ entry through dihydropyridine-sensitive Ca2+ channels. Cyclic nucleotides (cAMP and cGMP) lowered R in epithelial cells, the cGMP effect being interpreted as a feedback control on phosphoinositide turnover and resulting in the ability to re-establish cAMP production to levels incompatible with high PLC activity. In longitudinal muscular cells, the increase in R due to cAMP suggests the involvement of 5-hydroxytryptamine in stimulation of adenylate cyclase activity. Furthermore, results enabled the localization in epithelial cells of the transduction pathways mediating the actions of another antidiuretic factor extracted from the glandular lobes of the locust corpora cardiaca.

Video imaging of cytosolic Ca2+ in pancreatic beta-cells stimulated by glucose, carbachol, and ATP

In order to define the differences in the distribution of cytosolic free Ca2+ ([Ca2+]i) in pancreatic beta-cells stimulated with the fuel secretagogue glucose or the Ca(2+)-mobilizing agents carbachol and ATP, we applied digital video imaging to beta-cells loaded with fura-2.83% of the cells responded to glucose with an increase in [Ca2+]i after a latency of 117 +/- 24 s (mean +/- S.E., 85 cells). Of these cells, 16% showed slow wave oscillations (frequency 0.35/min). In order to assess the relationship between membrane potential and the distribution of the [Ca2+]i rise, digital image analysis and perforated patch-clamp methods were applied simultaneously. The system used allowed sufficient temporal resolution to visualize a subplasmalemmal Ca2+ transient due to a single glucose-induced action potential. Glucose could also elicit a slow depolarization which did not cause Ca2+ influx until the appearance of the first of a train of action potentials. [Ca2+]i rose progressively during spike firing. Inhibition of Ca2+ influx by EGTA abolished the glucose-induced rise in [Ca2+]i. In contrast, the peak amplitude of the [Ca2+]i response to carbachol was not significantly different in normal or in Ca(2+)-deprived medium. Occasionally, the increase of the [Ca2+]i rise was polarized to one area of the cell different from the subplasmalemmal rise caused by glucose. The amplitude of the response and the number of responding cells were significantly increased when carbachol was applied after the addition of high glucose (11.2 mM). ATP also raised [Ca2+]i and promoted both Ca2+ mobilization and Ca2+ influx. The intracellular distribution of [Ca2+]i was homogeneous during the onset of the response. A polarity in the [Ca2+]i distribution could be detected either in the descending phase of the peak or in subsequent peaks during [Ca2+]i oscillations caused by ATP. In the absence of extracellular Ca2+, the sequential application of ATP and carbachol revealed that carbachol was still able to raise [Ca2+]i after exhaustion of the ATP response. This may be due to desensitization to the former agonist, since the response occurred in the same area of the cell. These results reveal subtle differences in [Ca2+]i distribution following membrane depolarization with glucose or the application of Ca(2+)-mobilizing agonists.

Spontaneous and corticotropin-releasing factor-induced cytosolic calcium transients in corticotrophs

Spontaneous and CRF-stimulated changes in the cytosolic free calcium concentration ([Ca2+]i) were studied in two types of corticotrophs: 1) cultured human ACTH-secreting pituitary adenoma cells (hACTH cells), and 2) identified small ovoid corticotrophs cultured from normal rat pituitaries. [Ca2+]i was monitored in individual corticotrophs by dual emission microspectrofluorimetry using indo-1 as the intracellular fluorescent Ca2+ probe. In hACTH cells, [Ca2+]i measurements were carried out in combination with electrophysiological recordings obtained using whole cell patch-clamp techniques. It was shown that a single spontaneous Ca(2+)-dependent action potential led to a marked transient increase in [Ca2+]i in human tumoral corticotrophs. Spontaneous fluctuations in [Ca2+]i were also observed in unpatched corticotrophs whether derived from human pituitary tumors or normal rat tissue. Based on their striking kinetic features and their sensitivity to external Ca2+, we suggest that these spontaneous [Ca2+]i transients were the consequence of action potential firing. Under separate voltage-clamp (patch-clamp) conditions, tumor corticotrophs showed two Ca2+ current components: a low threshold, rapidly inactivating (T-type) current, and a higher threshold, slowly inactivating (L-type) current. The dihydropyridine Ca2+ channel blocker PN 200-110 (100 nM) abolished the L-type current without affecting the T-type current, while the inorganic Ca2+ channel blocker Cd2+ (200 microM) suppressed both Ca2+ currents. The Na+ channel blocker tetrodotoxin (5 microM) did not affect inward currents in tumor corticotrophs. Both L- and T-type voltage-gated Ca2+ channels were involved in controlling [Ca2+]i transients in both tumor and normal corticotrophs, inasmuch as Cd2+ (200 microM) abolished [Ca2+]i) transients, while PN 200-110 (100 nM) greatly diminished, but did not completely abolish, [Ca2+]i transients. The latter did not appear to depend on a voltage-dependent Na+ influx, since they were unaffected by tetrodotoxin (5 microM). Corticotrophs generate [Ca2+]i transients in response to the hypothalamic secretagogue CRF by acting on their membrane excitability. Indeed, we demonstrated in combined fluorescent and electrophysiological experiments that CRF (100 nM) had a coordinate action on human tumoral corticotrophs comprised of a modest depolarization and an increase in the frequency of both action potentials and subsequent [Ca2+]i transients. A coincident increase in the peak amplitude of the [Ca2+]i transient and after hyperpolarization was also observed in some CRF-stimulated cells. CRF (100 nM) evoked qualitatively similar [Ca2+]i patterns in human tumoral and normal rat corticotrophs not subjected to patch-clamping.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine A1 receptor-induced inhibition of Ca2+ transients linked to action potentials in clonal pituitary cells

Adenosine is a potent paracrine/autocrine feedback inhibitor of cell activation in a variety of tissues. Adenosine action was studied in pituitary cells, in which spontaneous electrical activity causes characteristic oscillations of the cytosolic free Ca2+ concentration, [Ca2+]i. Cells of the GH3B6 rat pituitary tumor line were studied by microspectrofluorimetry using the Ca2+ probes indo-1 and fura-2, in part in combination with electrophysiological tight seal whole cell recordings, obtained with the novel approach of patch perforation. It was demonstrated that adenosine receptor activation by N6-(R-phenyl-isopropyl)-adenosine (PIA) caused a block of electrical activity and abolished the ensuing alterations in [Ca2+]i. PIA mimicked the inhibitory action of somatostatin. Adenosine effects are mediated by A1 receptors in these cells and are antagonized by IBMX, an adenosine receptor blocker. PIA also suppressed action potentials that were elicited by the activation of protein kinase C with the phorbol ester PMA, or during the second phase of TRH action. In contrast, no interference was notable on TRH-induced intracellular Ca2+ mobilization. In addition to the abolition of Ca2+ transients, PIA lowers basal [Ca2+]i in some cells. It is proposed that in addition to the inhibition of adenylate cyclase, A1 receptor action on [Ca2+]i is an important element in the control of excitable pituitary cells.

Galanin evokes a cytosolic calcium bursting mode and hormone release in GH3/B6 pituitary cells

The effects of galanin on secretion and cytosolic free Ca2+ concentration ([Ca2+]i) have been studied in GH3/B6 pituitary cells. Prolactin (PRL) and growth hormone (GH) release was measured in column perifusion experiments; [Ca2+]i was monitored in single cells by dual emission microspectrofluorimetry using indo-1 as intracellular Ca2+ probe. Galanin (0.1-1 nM) caused PRL and GH release coincident with a modest rise in [Ca2+]i. The increase in [Ca2+]i comprises the establishment of characteristic long-lasting bursts of [Ca2+]i transients. Galanin acts on Ca2+ entry through voltage-gated Ca2+ channels since there was no response to the peptide when Cd2(+)-a Ca2+ channel blocker-was added to the bath solution. The stimulation of bursting activity by galanin may provide a fine Ca2(+)-signalling mechanism which maximally stimulates hormone release while avoiding refractory periods.