Cardiorespiratory reflexes in white sturgeon (Acipenser transmontanus): Lack of cardiac baroreflex response to blood pressure manipulation?

Arterial pressure (Pa) regulation is essential to adequately distribute nutrients to metabolizing tissues, remove wastes and avoid lesions associated with hypertension. In vertebrates, short-term Pa regulation is achieved through the baroreflex, which elicits inversely proportional changes in heart rate (fH) and vascular resistance to restore Pa. The cardiac limb of this reflex has been reported in all vertebrate groups studied to date: teleosts, amphibians, snakes, lizards, crocodiles, birds and mammals - which led to the suggestion that the baroreflex is an ancient trait present in all vertebrate species. However, it is not clear whether more basal groups of vertebrates, such as cyclostomes, elasmobranchs and chondrosteans, manifest baroreflex regulation of fH. Thus, the aim of this study was to determine whether the white sturgeon (Acipenser transmontanus; Chondrostei: Acipenseridae) exhibits a cardiac baroreflex. To do so, we induced Pa perturbations through injections of phenylephrine, sodium nitroprusside (SNP) and saline solution (hypervolemia), and examined possible fH baroreflex responses. We also investigated whether fH responses triggered by fright and chemoreflex were present in this species, in order to confirm the potential of sturgeon to perform reflexive cardiac adjustments. The findings indicate that A. transmontanus exhibits reflex bradycardia in response to fright and chemoreceptor stimulation, illustrating its capacity for short-term cardiac regulation. However, this species does not display baroreflex control of fH across its physiological range. This dissociation suggests that while the nervous and cardiovascular systems of A. transmontanus are primed for rapid reflex responses, a cardiac baroreflex mechanism remains absent.

Nordic socio-recreational ecosystem services in a hydropeaked river.

Fluctuating energy prices call for short-term river flow regulation at hydropower plants (HPPs), which can lead to hydropeaking - the pulsating water flow downstream from a HPP. Hydropeaking can affect land use areas of regulated rivers and subsequently their socio-recreational ecosystem services (SRESs). These areas often offer a range of services, such as swimming, boating, fishing, hiking, cycling, and berry picking. Such activities hold significant value in Nordic culture and for human wellbeing. We have examined how SRES land use areas are affected by hourly hydropeaking in a reach of the Kemijoki River in Finland. First, we determined the state of hydropeaking in the river by employing two indicators, normalized daily maximum flow difference and sub-daily flow ramping. Next, we looked at the spatiotemporal impacts of peaking hydrology using inundation maps derived from 2D-hydrodynamic modeling and a high-resolution land use map with clearly identified SRES areas. Finally, we examined the hazards to hydraulic safety in the river channel in the context of instream recreation. Our results show that hydropeaking levels in the study area remained consistently high throughout the entire study period, from 2010 to 2021. This was the case in all seasons except for the spring of 2013, 2016 and 2019. We determined that hydropeaking impacts on SRESs are mostly felt in the littoral zone (0.84 km2 i.e., 3.1 % of the study area) during the summer season as 25 % (0.21 km2) of this zone is influenced by hydropeaking. In addition, multiple recreational use areas in this zone, such as beaches, riparian forest, and summer cottages, were found to be affected by hydropeaking. The results show that most of the river channel becomes hydraulically unsafe during high ramping flows. The highest hazard to instream recreation opportunities is likely to occur during summer. Consequently, hydropeaking can threaten the social and recreational services of Nordic rivers.

The Readthrough Isoform AQP4ex Is Constitutively Phosphorylated in the Perivascular Astrocyte Endfeet of Human Brain.

AQP4ex is a recently discovered isoform of AQP4 generated by a translational readthrough mechanism. It is strongly expressed at the astrocyte perivascular endfeet as a component of the supramolecular membrane complex, commonly called orthogonal array of particles (OAP), together with the canonical isoforms M1 and M23 of AQP4. Previous site-directed mutagenesis experiments suggested the potential role of serine331 and serine335, located in the extended peptide of AQP4ex, in water channel activity by phosphorylation. In the present study we evaluated the effective phosphorylation of human AQP4ex. A small scale bioinformatic analysis indicated that only Ser335 is conserved in human, mouse and rat AQP4ex. The phosphorylation site of Ser335 was assessed through generation of phospho-specific antibodies in rabbits. Antibody specificity was first evaluated in binding phosphorylated peptide versus its unphosphorylated analog by ELISA, which was further confirmed by site-directed mutagenesis experiments. Western blot and immunofluorescence experiments revealed strong expression of phosphorylated AQP4ex (p-AQP4ex) in human brain and localization at the perivascular astrocyte endfeet in supramolecular assemblies identified by BN/PAGE experiments. All together, these data reveal, for the first time, the existence of a phosphorylated form of AQP4, at Ser335 in the extended sequence exclusive of AQP4ex. Therefore, we anticipate an important physiological role of p-AQP4ex in human brain water homeostasis.

Obestatin Downregulating Aquaporin 2 Plasma Membrane Distribution Through a Short-Term Regulatory Effect.

BACKGROUND: Previous studies have found that obestatin significantly inhibited water drinking and reduced the arginine vasopressin levels in the brain to decrease renal water reabsorption. However, obestatin is unable to cross the blood-brain barrier. Its effect on the body's kidney water metabolism in peripheral remains unknown. MATERIALS AND METHODS: Expression and subcellular distribution of aquaporin 2 (AQP2) were detected by immunoblotting and immunofluorescence in mouse inner medullary collecting duct-3 (mIMCD-3) cells and congestive heart failure model rats. Moreover, expression of phosphorylated AQP2 (P-AQP2; Ser256) in mIMCD-3 cells was evaluated by immunoblotting. RESULTS: After a 30-minute treatment with obestatin in mIMCD-3 cells and congestive heart failure model rats, the AQP2 plasma membrane distribution decreased, while AQP2 protein level, P-AQP2 (Ser256) protein level and phosphorylation ratio of AQP2 showed no significant change. CONCLUSIONS: These findings suggest that obestatin has a short-term regulatory effect on the AQP2 plasma membrane distribution. In addition, obestatin decreases the APQ2 plasma membrane distribution probably by promoting the endocytosis of AQP2.

Photosynthesis Control: An underrated short-term regulatory mechanism essential for plant viability.

Regulation of photosynthetic electron transport provides efficient performance of oxygenic photosynthesis in plants. During the last 15 years, the molecular bases of various photosynthesis short-term regulatory processes have been elucidated, however the wild type-like phenotypes of mutants lacking of State Transitions, Non Photochemical Quenching, or Cyclic Electron Transport, when grown under constant light conditions, have also raised doubts about the acclimatory significance of these short-regulatory mechanisms on plant performance. Interestingly, recent studies performed by growing wild type and mutant plants under field conditions revealed a prominent role of State Transitions and Non Photochemical Quenching on plant fitness, with almost no effect on vegetative plant growth. Conversely, the analysis of plants lacking the regulation of electron transport by the cytochrome b6f complex, also known as Photosynthesis Control, revealed the fundamental role of this regulatory mechanism in the survival of young, developing seedlings under fluctuating light conditions.