Using H I spectra obtained with the Lovell telescope (FWHM ∼ 12 arcmin) we present maps showing the H I distribution and velocity structure of an intermediate‐velocity cloud (IVC; vLSR ∼ 70 km s−1) which is observed in the general direction of the globular cluster M15. The gas is shown to be clumpy in nature and we examine its position and velocity structure.  The IVC is detected in absorption in the Ca II K line towards five cluster stars in intermediate resolution spectra obtained with ISIS/WHT and in high resolution UES/WHT Na I D line spectra of two cluster stars (II‐75; IV‐38). The clumpy nature of the gas is indicated by the Na I and K I spectra obtained in the II‐75 and IV‐38 sightlines, which have angular separation ∼ 3.5 arcmin. The IVC is detected in K I in the higher column density II‐75 sightline; this appears to be the first detection of IVC or HVC gas in K I.  The IVC gas towards M15 has a similar velocity to that observed towards HD 203664, some 3.1° away from the cluster. Similarities in the IVC gas velocity suggest a gas structure that extends across both sightlines, although gas column densities are considerably higher towards M15. For a common feature, this would place the M15 IVC at a height above the Galactic plane (z‐distance) of ≲ 1.5 kpc based on the Little et al. estimate of the HD 203664 distance. From the fine‐scale structure and column density observations, estimates are made of the space density of the small‐scale concentrations. However, these remain uncertain and the present observations emphasize the need for higher spatial and spectral resolution studies to provide firmer estimates of cloud properties.  We report also on a radio H I and Ca II line survey towards a sample of 24 stars over a wider field. This was carried out in an attempt to detect any wider distribution of the IVC gas and to place better limits on its distance. Although these observations are of sufficient spectral quality, no new optical detections are reported.

Here we make a new study of the behaviour of the Na i/K i column density ratio in the interstellar medium, using a sample of new observations of 28 stars obtained at the Nordic Optical Telescope (NOT) in 1996 and 1997, and previously published observations (obtained by some of the authors) of 21 stars. The sightlines cover a range of distances and directions, including into the Galactic halo. We make use of new observations of the Na i ultraviolet (UV) doublet for some 18 stars. This doublet is much weaker than the Na i D doublet and so is less susceptible to saturation effects, and it is well known that it can be used to obtain more accurate Na i column densities with a smaller error range. We find an average N(Na i)/N(K i) ratio from the Na i UV data of about 90, which is rather higher than that found previously by Hobbs and Lequeux. The Na UV–K i ratio shows a small increase in value with increasing column density, while we also find a sample of low N(Na i)/N(K i) ratio clouds generally seen towards distant objects on high‐latitude sightlines that reach into the halo, so that the ratio decreases more sharply at lower column densities. As the values of the ratio for these halo clouds (10–20) bracket the cosmic Na/K abundance ratio, we suggest that these ratios result from a harder radiation field in the lower halo, such that the ionized fractions of Na i and K i become similar. Clearly caution needs to be applied in using any kind of ‘standard value’ for the Na i/K i column density ratio.

Regulation of cytoplasmic free calcium concentration is believed to be important in the response of platelets to external stimuli. A relatively new fluorescent calcium indicator, indo-1, has properties by which alterations of cytoplasmic calcium can be evaluated in single platelets by flow cytometry. Activation of platelets at a temperature lower than 37 degrees C allows examination of the heterogeneity of intracellular free calcium levels and can distinguish variations among platelets in the initiation, duration, and magnitude of calcium fluxes. The clear advantage of flow cytometric analysis of platelet cytosolic calcium is that stimulus-response coupling can now be studied on a single cell basis. Platelets were activated by addition of human alpha- thrombin or ADP at 37 degrees C or at room temperature (22 degrees C). Activation at 37 degrees C approaches more closely an in vivo response and, as expected, increases in cytosolic calcium occurred within seconds of agonist addition. Transient increases in cytoplasmic calcium levels occurred when platelets were challenged with a low concentration of agonist. Heterogeneity in cytoplasmic calcium levels was also observed at 10(-5) mol/L ADP and 0.1 U/mL alpha-thrombin. Some of this heterogeneity was no longer observed at higher concentrations of agonist (10(-4) mol/L ADP and 0.5 U/mL thrombin), suggesting that a sufficient magnitude of signal is required to induce changes in platelet cytosolic calcium. Light-scatter properties of the activated platelets were also monitored simultaneously and showed changes in response to both agonists. The ability to measure changes in cytoplasmic free calcium by ratio flow cytofluorimetry provides a new approach to study of the role of alterations in intracellular calcium in response to agonists acting through different membrane receptors as well as providing a sensitive technique to detect functional subpopulations of platelets.

The present studies were designed to investigate the mechanism by which neuropeptide-Y (NPY) augments the effect of LHRH to stimulate the release of LH from cultured rat anterior pituitary cells. Anterior pituitary cells from ovariectomized rats were enzymatically dispersed, cultured for 3 days, and then exposed to various secretagogues during 3-h incubations. As reported by this laboratory previously, NPY alone (100 nM) did not affect LH release, but significantly enhanced the LH response to 1 nM LHRH. This facilitatory action of NPY was mimicked by the dihydropyridine Ca2+ channel agonist Bay K 8644 (1 microM), and the enhancement of LHRH-induced LH release by either NPY or Bay K 8644 was prevented by the dihydropyridine antagonist nitrendipine (1 microM). Nitrendipine alone reduced the response to LHRH by approximately 25%, but did not affect basal LH release. In contrast, NPY failed to amplify the release of PRL in response to TRH, another Ca2(+)-mobilizing hormone. To test whether NPY also enhances the increase in cytosolic Ca2+ induced by LHRH, anterior pituitary cells were acutely dispersed into single cell suspensions, loaded with the fluorescent Ca2+ probe Indo-1 AM, and analyzed with a UV laser in an EPICS-753 flow cytometer at a rate of 500 cells/sec for 200 sec. The ratio of intracellular fluorescence resulting from Ca2+ bound to the Indo-1 to the fluorescence from Indo-1 alone (Indo-1 ratio), which is an index of the concentration of free cytosolic Ca2+, was determined for each cell. Approximately 7% of anterior pituitary cells responded to LHRH (1 or 10 nM) with significant increases in Indo-1 ratios, indicative of an increase in the concentration of free cytosolic Ca2+. EGTA (2.5 mM) reduced the basal Indo-1 ratios and attenuated, but did not abolish, the initial increase in response to LHRH, consistent with the initial extracellular Ca2+ influx-independent phase of the response to LHRH. NPY alone (100 nM) did not affect the Indo-1 ratios in anterior pituitary cells, but pretreatment with the peptide for 10 min before the scans significantly augmented the Indo-1 ratio response to 10 nM LHRH. This effect of NPY was also blocked by EGTA. Taken together, these biochemical and pharmacological studies suggest that NPY enhances the release of LH stimulated by LHRH by increasing extracellular Ca2+ entry, possibly by selectively affecting that component of the response involving dihydropyridine-sensitive L-type voltage-sensitive Ca2+ channels during the initial stages of the cellular response to LHRH.