Sperm competition risk drives plasticity in seminal fluid composition

Background Ejaculates contain a diverse mixture of sperm and seminal fluid proteins, the combination of which is crucial to male reproductive success under competitive conditions. Males should therefore tailor the production of different ejaculate components according to their social environment, with particular sensitivity to cues of sperm competition risk (i.e. how likely it is that females will mate promiscuously). Here we test this hypothesis using an established vertebrate model system, the house mouse (Mus musculus domesticus), combining experimental data with a quantitative proteomics analysis of seminal fluid composition. Our study tests for the first time how both sperm and seminal fluid components of the ejaculate are tailored to the social environment. Results Our quantitative proteomics analysis reveals that the relative production of different proteins found in seminal fluid – i.e. seminal fluid proteome composition – differs significantly according to cues of sperm competition risk. Using a conservative analytical approach to identify differential expression of individual seminal fluid components, at least seven of 31 secreted seminal fluid proteins examined showed consistent differences in relative abundance under high versus low sperm competition conditions. Notably three important proteins with potential roles in sperm competition – SVS 6, SVS 5 and CEACAM 10 – were more abundant in the high competition treatment groups. Total investment in both sperm and seminal fluid production also increased with cues of heightened sperm competition risk in the social environment. By contrast, relative investment in different ejaculate components was unaffected by cues of mating opportunities. Conclusions Our study reveals significant plasticity in different ejaculate components, with the production of both sperm and non-sperm fractions of the ejaculate strongly influenced by the social environment. Sperm competition risk is thus shown to be a key factor in male ejaculate production decisions, including driving plasticity in seminal fluid composition

A Direct Demonstration of Closed-State Inactivation of K+ Channels at Low pH

Lowering external pH reduces peak current and enhances current decay in Kv and Shaker-IR channels. Using voltage-clamp fluorimetry we directly determined the fate of Shaker-IR channels at low pH by measuring fluorescence emission from tetramethylrhodamine-5-maleimide attached to substituted cysteine residues in the voltage sensor domain (M356C to R362C) or S5-P linker (S424C). One aspect of the distal S3-S4 linker α-helix (A359C and R362C) reported a pH-induced acceleration of the slow phase of fluorescence quenching that represents P/C-type inactivation, but neither site reported a change in the total charge movement at low pH. Shaker S424C fluorescence demonstrated slow unquenching that also reflects channel inactivation and this too was accelerated at low pH. In addition, however, acidic pH caused a reversible loss of the fluorescence signal (pKa = 5.1) that paralleled the reduction of peak current amplitude (pKa = 5.2). Protons decreased single channel open probability, suggesting that the loss of fluorescence at low pH reflects a decreased channel availability that is responsible for the reduced macroscopic conductance. Inhibition of inactivation in Shaker S424C (by raising external K+ or the mutation T449V) prevented fluorescence loss at low pH, and the fluorescence report from closed Shaker ILT S424C channels implied that protons stabilized a W434F-like inactivated state. Furthermore, acidic pH changed the fluorescence amplitude (pKa = 5.9) in channels held continuously at −80 mV. This suggests that low pH stabilizes closed-inactivated states. Thus, fluorescence experiments suggest the major mechanism of pH-induced peak current reduction is inactivation of channels from closed states from which they can activate, but not open; this occurs in addition to acceleration of P/C-type inactivation from the open state

Measures of CNS-Autonomic Interaction and Responsiveness in Disorder of Consciousness

Neuroimaging studies have demonstrated functional interactions between autonomic (ANS) and brain (CNS) structures involved in higher brain functions, including attention and conscious processes. These interactions have been described by the Central Autonomic Network (CAN), a concept model based on the brain-heart two-way integrated interaction. Heart rate variability (HRV) measures proved reliable as non-invasive descriptors of the ANS-CNS function setup and are thought to reflect higher brain functions. Autonomic function, ANS-mediated responsiveness and the ANS-CNS interaction qualify as possible independent indicators for clinical functional assessment and prognosis in Disorders of Consciousness (DoC). HRV has proved helpful to investigate residual responsiveness in DoC and predict clinical recovery. Variability due to internal (e.g. homeostatic and circadian processes) and environmental factors remains a key independent variable and systematic research with this regard is warranted. The interest in bidirectional ANS-CNS interactions in a variety of physiopathological conditions is growing, however these interactions have not been extensively investigated in DoC. In this brief review we illustrate the potentiality of brain-heart investigation by means of HRV analysis in assessing patients with DoC. The authors’ opinion is that this easy, inexpensive and non-invasive approach may provide useful information in the clinical assessment of this challenging patient population

The Persistence of Objects

A public seminar chaired by Declan Long on the exhibition 'The Persistence of Objects' in Lismore, June 2016, with contributions from curators Katrina Brown and Kitty Anderson and artists Steven Claydon, Gabriel Kuri and Hayley Tompkins

Kinetic analysis of the effects of H+ or Ni2+ on Kv1.5 current shows that both ions enhance slow inactivation and induce resting inactivation

External H+ and Ni2+ ions inhibit Kv1.5 channels by increasing current decay during a depolarizing pulse and reducing the maximal conductance. Although the former may be attributed to an enhancement of slow inactivation occurring from the open state, the latter cannot. Instead, we propose that the loss of conductance is due to the induction, by H+ or Ni2+, of a resting inactivation process. To assess whether the two inactivation processes are mechanistically related, we examined the time courses for the onset of and recovery from H+- or Ni2+-enhanced slow inactivation and resting inactivation. Compared to the time course of H+- or Ni2+-enhanced slow inactivation at +50 mV, the onset of resting inactivation induced at −80 mV with either ion involves a relatively slower process. Recovery from slow inactivation under control conditions was bi-exponential, indicative of at least two inactivated states. Recovery following H+- or Ni2+-enhanced slow inactivation or resting inactivation had time constants similar to those for recovery from control slow inactivation, although H+ and Ni2+ biased inactivation towards states from which recovery was fast and slow, respectively. The shared time constants suggest that the H+- and Ni2+-enhanced slow inactivated and induced resting inactivated states are similar to those visited during control slow inactivation at pH 7.4. We conclude that in Kv1.5 H+ and Ni2+ differentially enhance a slow inactivation process that involves at least two inactivated states and that resting inactivation is probably a close variant of slow inactivation

Single Channel Analysis Reveals Different Modes of Kv1.5 Gating Behavior Regulated by Changes of External pH

In the voltage-gated potassium channel Kv1.5, extracellular acidification decreases the peak macroscopic conductance and accelerates slow inactivation. To better understand the mechanistic basis for these two effects, we recorded unitary currents of Kv1.5 expressed in a mouse cell line (ltk(−)) using the voltage clamp technique both in cell-attached and excised outside-out patches. Single channel current amplitude at 100 mV (1.7 ± 0.2 pA at pH 7.4, 1.7 ± 0.2 pA at pH 6.4) and the single channel conductance between 0 and 100 mV (11.8 ± 0.6 pS at pH 7.4 and 11.3 ± 0.8 pS at pH 6.4) did not change significantly with pH. External acidification significantly decreased the number of active sweeps, and this reduction in channel availability accounted for most of the reduction of the peak macroscopic current. The results of runs analyses suggested the null sweeps occur in clusters, and the rate constants for the transition between clusters of null and active sweeps at pH 6.4 were slow (0.12 and 0.18 s(−1), to and from the active clusters, respectively). We propose that low pH facilitates a shift from an available mode (mode A) into an unavailable mode of gating (mode U). In addition to promoting mode U gating, external acidification accelerates depolarization-induced inactivation, which is manifest at the single channel level as a reduction of the mean burst length and an apparent increase of the interburst interval. These effects of external acidification, which are thought to reflect the protonation of a histidine residue in the turret (H-463), point to an important role for the turret in the regulation of channel availability and inactivation