Characterization of a calcium-activated potassium channel from rabbit intestinal smooth muscle incorporated into planar bilayers

Summary Interaction of vesicles from a microsomal fraction of rabbit intestinal smooth muscle with planar bilayers promotes the incorporation of a large conductance potassium-selective channel. The channel conductance fluctuates between two states: closed and open and the fraction of time the channel dwells in the open state is a function of the electric potential difference and the calcium concentrations. This channel seems to correspond to a Ca-activated K channel described by other authors in smooth muscle cells with the patch-clamp technique. Single-channel conductance is a saturating function of the potassium concentration. The relationship between conductance and concentration cannot be described by a hyperbolic function, suggesting multiple occupancy of the channel. The single-channel conductance is 230 pS in symmetrical 0.1m KCl. Current is a linear function of the applied voltage in the range between –100 and +100 mV, at concentrations of 0.1m KCl or higher. At lower concentrations, current-to-voltage curves bend symmetrically to the voltage axis. Sodium, lithium and cesium ions do not pass through the channel and the permeability for Rb is 66% that of potassium. All these alkali cations and Ca²⁺ block the channel in a voltage-dependent manner. A two-site three-barrier model on Eyring absolute reaction rate theory can account for the conduction and blocking characteristics.     

Electrophysiological relations between the superior colliculus and the red nucleus in the cat.

The electrical activity of single units located in the parvicellular part of the red nucleus (pRP) was recorded extracellularly in nitrous oxide anesthetized and C1-transected adult cats. In this area, neurons were found to respond to electrical stimulation applied to intermediate and deep layers of the right superior colliculus (SC). Forty neurons located in the pRN of both sides were studied. Three neurons out of 18 (16.6%) located in the contralateral pRN and six neurons out of 22 (27.3%) located in the ipsilateral pRN were driven by the right SC stimulation. The pRN neurons were separated into four groups according to the latency response to the SC stimulation: 1) 0.6-1.9 ms, 2) 2-4 ms, 3) 4-6 ms, 4) variable latency responses. Each of these four groups of neurons showed a particular pattern of discharge, even though their discharge frequency showed a strong consistency. Four pRN neurons, which responded to SC stimulation, showed a significant correlation with spontaneous horizontal eye movements of saccadic type. It is known that the SC represents one of the main outputs of the striato-nigral motor system. The relation between the SC and the pRN described in the present study suggest that connections exist between the cortico-rubral and the striato-nigral systems, since both have the SC as a common output structure. It is likely, therefore, that the cortico-rubral-SC system is involved in the control of oculomotor functions, and that the SC may serve to establish interactions between systems concerned with eye movements.     

Behavioral Syndromes in Stable Social Groups: An Artifact of External Constraints?

Individuals of many species differ consistently in their behavioral reactions toward different stimuli, such as predators, rivals, and potential mates. These typical reactions, described as ‘behavioral syndromes’ or ‘personalities,’ appear to be heritable and therefore subject to selection. We studied behavioral syndromes in 36 male fowl living in 12 social groups and found that individuals behaved consistently over time. Furthermore, responses to different contexts (anti‐predator, foraging, and territorial) were inter‐correlated, suggesting that males exhibited comparable behavioral traits in these functionally distinct situations. We subsequently isolated the same roosters and conducted tests in a ‘virtual environment,’ using high‐resolution digital video sequences to simulate the anti‐predator, foraging, and territorial contexts that they had experienced outdoors. Under these controlled conditions, repeatability persisted but individual responses to the three classes of stimuli failed to predict one another. These were instead context‐specific. In particular, production of each type of vocal signal was independent, implying that calls in the repertoire are controlled by distinct mechanisms. Our results show that extrinsic factors, such as social position, can be responsible for the appearance of traits that could readily be mistaken for the product of endogenous characters.     

Effect of Rocking Movements on Respiration

For centuries, rocking has been used to promote sleep in babies or toddlers. Recent research suggested that relaxation could play a role in facilitating the transition from waking to sleep during rocking. Breathing techniques are often used to promote relaxation. However, studies investigating head motions and body rotations showed that vestibular stimulation might elicit a vestibulo-respiratory response, leading to an increase in respiration frequency. An increase in respiration frequency would not be considered to promote relaxation in the first place. On the other hand, a coordination of respiration to rhythmic vestibular stimulation has been observed. Therefore, this study aimed to investigate the effect of different movement frequencies and amplitudes on respiration frequency. Furthermore, we tested whether subjects adapt their respiration to movement frequencies below their spontaneous respiration frequency at rest, which could be beneficial for relaxation. Twenty-one healthy subjects (24–42 years, 12 males) were investigated using an actuated bed, moving along a lateral translation. Following movement frequencies were applied: +30%, +15%, -15%, and -30% of subjects’ rest respiration frequency during baseline (no movement). Furthermore, two different movement amplitudes were tested (Amplitudes: 15 cm, 7.5 cm; movement frequency: 0.3 Hz). In addition, five subjects (25–28 years, 2 males) were stimulated with their individual rest respiration frequency. Rocking movements along a lateral translation caused a vestibulo-respiratory adaptation leading to an increase in respiration frequency. The increase was independent of the applied movement frequencies or amplitudes but did not occur when stimulating with subjects’ rest respiration frequency. Furthermore, no synchronization of the respiration frequency to the movement frequency was observed. In particular, subjects did not lower their respiration frequency below their resting frequency. Hence, it was not feasible to influence respiration in a manner that might be considered beneficial for relaxation.     

Widespread reliance on olfactory sex and species identification by lyssomanine and spartaeine jumping spiders

Jumping spiders (Salticidae) are renowned for their exceptional vision, but this does not preclude use of other senses. Here we provide evidence that olfactory pheromones are widespread in the Spartaeinae and Lyssomaninae, two subfamilies regarded as basal clades within the Salticidae. Pheromone use by salticids was tested in a series of experiments: males were tested with the odour of conspecific females, heterospecific females, and conspecific males, and females were tested with the odour of conspecific males. With seven of the 29 species tested, we also tested males using the draglines of conspecific females (spider absent) as the odour source. Males of all species tested were attracted to the odour of conspecific females and to the odour of the draglines of conspecific females. There was no evidence of males responding to the odour of heterospecific females or conspecific males, or of females responding to the odour of conspecific males. These findings suggest that it is primarily males that respond to olfactory sex pheromones, consistent with the apparent trend within spiders of males more actively searching for females and females placing greater emphasis on mate‐choice decisions. Compared with most salticid groups, lyssomanines and spartaeines are unusually sedentary and this lifestyle may favour olfactory mate searching. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107 , 664–677.     

ESCRT-III-Associated Protein ALIX Mediates High-Affinity Phosphate Transporter Trafficking to Maintain Phosphate Homeostasis in Arabidopsis

Prior to the release of their cargoes into the vacuolar lumen, sorting endosomes mature into multivesicular bodies (MVBs) through the action of ENDOSOMAL COMPLEX REQUIRED FOR TRANSPORT (ESCRT) protein complexes. MVB-mediated sorting of high-affinity phosphate transporters (PHT1) to the vacuole limits their plasma membrane levels under phosphate-sufficient conditions, a process that allows plants to maintain phosphate homeostasis. Here, we describe ALIX, a cytosolic protein that associates with MVB by interacting with ESCRT-III subunit SNF7 and mediates PHT1;1 trafficking to the vacuole in Arabidopsis thaliana. We show that the partial loss-of-function mutant alix-1 displays reduced vacuolar degradation of PHT1;1. ALIX derivatives containing the alix-1 mutation showed reduced interaction with SNF7, providing a simple molecular explanation for impaired cargo trafficking in alix-1 mutants. In fact, the alix-1 mutation also hampered vacuolar sorting of the brassinosteroid receptor BRI1. We also show that alix-1 displays altered vacuole morphogenesis, implying a new role for ALIX proteins in vacuolar biogenesis, likely acting as part of ESCRT-III complexes. In line with a presumed broad target spectrum, the alix-1 mutation is pleiotropic, leading to reduced plant growth and late flowering, with stronger alix mutations being lethal, indicating that ALIX participates in diverse processes in plants essential for their life.     

The Anx7(+/-) knockout mutation alters electrical and secretory responses to Ca(2+)-mobilizing agents in pancreatic β-cells

Insulin secretion from the pancreatic β-cell is controlled by changes in membrane potential and intracellular Ca(2+). The contribution of intracellular Ca(2+) stores to this process is poorly understood. We have previously shown that β-cells of mice lacking one copy of the Annexin 7 gene (Anx7(+/-)) express reduced levels of IP(3) receptors and defects in IP(3)-dependent Ca(2+) signaling. To further elucidate the effect of the Anx7(+/-) mutation on signaling related to intracellular Ca(2+) stores in the β-cell, we measured the effects of Ca(2+) mobilizing agents on electrical activity, intracellular Ca(2+) and insulin secretion in control and mutant β-cells. We found that the muscarinic agonist carbachol and the ryanodine receptor agonists caffeine and 4-chloro-m-cresol had more potent depolarizing effects on Anx7(+/-) β-cells compared to controls. Accordingly, glucose-induced insulin secretion was augmented to a greater extent by caffeine in mutant islets. Surprisingly, ryanodine receptor-mediated Ca(2+) mobilization was not affected by the Anx7(+/-) mutation, suggesting that the mechanism underlying the observed differences in electrical and secretory responsiveness does not involve intracellular Ca(2+) stores. Our results provide evidence that both IP3 receptors and ryanodine receptors play important roles in regulating β-cell membrane potential and insulin secretion, and that the Anx7(+/-) mutation is associated with alterations in the signaling pathways related to these receptors.     

Reconstitution of recycling from the phagosomal compartment in streptolysin O-permeabilized macrophages: role of Rab11

By phagocytosis, macrophages engulf large particles, microorganisms and senescent cells in vesicles called phagosomes. Many internalized proteins rapidly shuttle back to the plasma membrane following phagosome biogenesis. Here, we report a new approach to the study of recycling from the phagosomal compartment: streptolysin O- (SLO) permeabilized macrophages. In this semi-intact cell system, energy and cytosol are required to efficiently reconstitute recycling transport. Addition of GDPbetaS strongly inhibits this transport step, suggesting that a GTP-binding protein modulates the dynamics of cargo exit from the phagosomal compartment. GTPases of the Rab family control vesicular trafficking, and Rab11 is involved in transferrin receptor recycling. To unravel the role of Rab11 in the phagocytic pathway, we added recombinant proteins to SLO-permeabilized macrophages. Rab11:S25N, a negative mutant, strongly diminishes the release of recycled proteins from phagosomes. In contrast, wild type Rab11 and its positive mutant (Rab11:Q70L) favor this vesicular transport event. Using biochemical and morphological assays, we confirm that overexpression of Rab11:S25N substantially decreases recycling from phagosomes in intact cells. These findings show the requirement of a functional Rab11 for the retrieval to the plasma membrane of phagosomal content. SLO-permeabilized macrophages likely constitute a useful tool to identify new molecules involved in regulating transport along the phagocytic pathway.