Autonomic and sensory nerve modulation of peristalsis in the upper urinary tract.

The primary function of the upper urinary tract is to propel urine and various water-soluble toxic compounds from the kidneys to the bladder for storage and evacuation to maintain body ionic balance and contribute to the regulation of blood volume and pressure. The mechanism by which the upper urinary tract propels urine has long been considered to be myogenic in origin as peristaltic contractions in vivo and in vitro (pyeloureteric peristalsis) propagate in a manner little affected by drugs that block nerve conduction or the sympathetic and parasympathetic transmission. However, it is now well established that the release of intrinsic prostaglandins and neuropeptides from primary sensory nerves (PSNs) helps to maintain pyeloureteric peristalsis. Electrical field stimulation of PSNs evokes species-specific positive inotropic and chronotropic effects that have been attributed to release of excitatory tachykinins superimposed on negative inotropic and chronotropic effects associated with the release of calcitonin gene related peptide (CGRP), a rise in cellular cyclic-adenosine monophosphate (cAMP) and a protein kinase A-dependent activation of glibenclamide-sensitive ATP-dependent K+ (KATP) channels. This review summarises the existing evidence of the nervous control of the upper urinary tract and recent evidence suggesting that the autonomic innervation may indirectly modulate pyeloureteric peristalsis via the activation of PSN nicotinic receptors and via the modulation of KV7 channels located on interstitial cells within the renal pelvis wall.

Nicotinic receptor activation on primary sensory afferents modulates autorhythmicity in the mouse renal pelvis.

BACKGROUND AND PURPOSE: The modulation of the spontaneous electrical and Ca(2+) signals underlying pyeloureteric peristalsis upon nicotinic receptor activation located on primary sensory afferents (PSAs) was investigated in the mouse renal pelvis. EXPERIMENTAL APPROACH: Contractile activity was followed using video microscopy, electrical and Ca(2+) signals in typical and atypical smooth muscle cells (TSMCs and ASMCs) within the renal pelvis were recorded separately using intracellular microelectrodes and Fluo-4 Ca(2+) imaging. KEY RESULTS: Nicotine and carbachol (CCh; 1-100 µM) transiently reduced the frequency and increased the amplitude of spontaneous phasic contractions in a manner unaffected by muscarininc antagonists, 4-DAMP (1,1-dimethyl-4-diphenylacetoxypiperidinium iodide) and pirenzipine (10 nM) or L-NAME (L-Nω-nitroarginine methyl ester; 200 µM), inhibitor of NO synthesis, but blocked by the nicotinic antagonist, hexamethonium or capsaicin, depletor of PSA neuropeptides. These negative chronotropic and delayed positive inotropic effects of CCh on TSMC contractions, action potentials and Ca(2+) transients were inhibited by glibenclamide (Glib; 1 µM), blocker of ATP-dependent K (KATP) channels. Nicotinic receptor-evoked inhibition of the spontaneous Ca(2+) transients in ASMCs was prevented by capsaicin but not Glib. In contrast, the negative inotropic and chronotropic effects of the non-selective COX inhibitor indomethacin were not prevented by Glib. CONCLUSIONS AND IMPLICATIONS: The negative chronotropic effect of nicotinic receptor activation results from the release of calcitonin gene-related peptide (CGRP) from PSAs, which suppresses Ca(2+) signalling in ASMCs. PSA-released CGRP also evokes a transient hyperpolarization in TSMCs upon the opening of KATP channels, which reduces contraction propagation but promotes the recruitment of TSMC Ca(2+) channels that underlie the delayed positive inotropic effects of CCh.

Performances under representative pressure and temperature conditions of the gas chromatography-mass spectrometry space experiment to investigate Titan's atmospheric composition.

In the frame of the calibration of the aerosol collector and pyrolyser, and gas chromatography-mass spectrometry experiments of the Huygens probe arrived at Titan, systematic experimental studies were led to estimate the influence of the operating conditions on the analyses that should have been achieved in the Titan's atmosphere. The primary objective of this study was to estimate the influence of operating conditions variations induced by (i) instrumental modifications made shortly before the probe launch which can have changed the operating pressures; (ii) the change of the probe environmental conditions (pressure, temperature) during its descent in the atmosphere; (iii) a possible deviation of pressure and temperature regulations from their nominal values because of the long journey of the instrument in space, or of other external events. The secondary objective of this work was to create an analytical database that can be used as a reference to treat the chromatograms obtained in situ, and help to identify chromatographically the analyzed species, complementary to mass spectrometry. Beyond the application to a specific instrument, this work was also useful to experimentally estimate the fundamental evolution of the separation as a function of the changes of operating conditions with time. The obtained results show (i) the significant influence of inlet and outlet pressure variation on the time of analysis, but not on the separation power. It thus enables to significantly shorten the analysis duration, and thus to analyze more compounds within the fixed time of analysis of the instrument; (ii) the significant influence of temperature on the retention. In this frame, the enthalpies of exchange between the gas phase and the stationary phase of the species were determined to be used to retrieve the analyzed species in case of deviation of the operating temperature; (iii) that the possible aging of the columns does not have influence on the columns efficiency and separation power; (iv) the analytical capabilities of the gas chromatography-mass spectrometry experiment within operating conditions representative of those encountered in situ. Finally, in spite of possible operating condition changes, it is shown that results coming from the gas chromatograph-mass spectrometer experiment, which are currently under analysis, could bring important information on the Titan's atmosphere and its history.

Complex organic matter in Titan's atmospheric aerosols from in situ pyrolysis and analysis.

Aerosols in Titan's atmosphere play an important role in determining its thermal structure. They also serve as sinks for organic vapours and can act as condensation nuclei for the formation of clouds, where the condensation efficiency will depend on the chemical composition of the aerosols. So far, however, no direct information has been available on the chemical composition of these particles. Here we report an in situ chemical analysis of Titan's aerosols by pyrolysis at 600 degrees C. Ammonia (NH3) and hydrogen cyanide (HCN) have been identified as the main pyrolysis products. This clearly shows that the aerosol particles include a solid organic refractory core. NH3 and HCN are gaseous chemical fingerprints of the complex organics that constitute this core, and their presence demonstrates that carbon and nitrogen are in the aerosols.