Stochastic resonance as a collective property of ion channel assemblies

By use of a stochastic generalization of the Hodgkin-Huxley model we investigate both the phenomena of stochastic resonance (SR) and coherence resonance (CR) in variable size patches of an excitable cell membrane. Our focus is on the challenge how internal noise stemming from individual ion channels does affect collective properties of the whole ensemble. We investigate both an unperturbed situation with no applied stimuli and one in which the membrane is stimulated externally by a periodic signal and additional external noise. For the nondriven case, we demonstrate the existence of an optimal size of the membrane patch for which the internal noise causes a most regular spike activity. This phenomenon shall be termed intrinsic CR. In presence of an applied periodic stimulus we demonstrate that the signal-to-noise ratio (SNR) exhibits SR vs. decreasing patch size, or vs. increasing internal noise strength, respectively. Moreover, we demonstrate that conventional SR vs. the external noise intensity occurs only for sufficiently large membrane patches, when the intensity of internal noise is below its optimal level. Thus, biological SR seemingly is rooted in the collective properties of large ion channel ensembles rather than in the individual stochastic dynamics of single ion channels.Comment: 9 pages, 2 figure

Capacitance fluctuations causing channel noise reduction in stochastic Hodgkin-Huxley systems

Voltage-dependent ion channels determine the electric properties of axonal cell membranes. They not only allow the passage of ions through the cell membrane but also contribute to an additional charging of the cell membrane resulting in the so-called capacitance loading. The switching of the channel gates between an open and a closed configuration is intrinsically related to the movement of gating charge within the cell membrane. At the beginning of an action potential the transient gating current is opposite to the direction of the current of sodium ions through the membrane. Therefore, the excitability is expected to become reduced due to the influence of a gating current. Our stochastic Hodgkin-Huxley like modeling takes into account both the channel noise -- i.e. the fluctuations of the number of open ion channels -- and the capacitance fluctuations that result from the dynamics of the gating charge. We investigate the spiking dynamics of membrane patches of variable size and analyze the statistics of the spontaneous spiking. As a main result, we find that the gating currents yield a drastic reduction of the spontaneous spiking rate for sufficiently large ion channel clusters. Consequently, this demonstrates a prominent mechanism for channel noise reduction.Comment: 18 page

Perceptions of Problem Behavior in Adolescents’ Families: Perceiver, Target, and Family Effects

Considerable research has focused on the reliability and validity of informant reports of family behavior, especially maternal reports of adolescent problem behavior. None of these studies, however, has based their orientation on a theoretical model of interpersonal perception. In this study we used the social relations model (SRM) to examine family members’ reports of each others’ externalizing and internalizing problem behavior. Two parents and two adolescents in 69 families rated each others’ behavior within a round-robin design. SRM analysis showed that within-family perceptions of externalizing and internalizing behaviors are consistently due to three sources of variance; perceiver, target, and family effects. A family/contextual effect on informant reports of problem behavior has not been previously reported

Minimal state models for ionic channels involved in glucagon secretion

Pancreatic alpha cells synthesize and release glucagon. This hormone along with insulin, preserves blood glucose levels within a physiological range. During low glucose levels, alpha cells exhibit electrical activity related to glucagon secretion. In this paper, we introduce minimal state models for those ionic channels involved in this electrical activity in mice alpha cells. For estimation of model parameters, we use Monte Carlo algorithms to fit steadystate channel currents. Then, we simulate dynamic ionic currents following experimental protocols. Our aims are 1) To understand the individual ionic channel functioning and modulation that could affect glucagon secretion, and 2) To simulate ionic currents actually measured in voltage-clamp alpha-cell experiments in mice. Our estimations indicate that alpha cells are highly permeable to sodium and potassium which mainly manage action potentials. We have also found that our estimated N-type calcium channel population and density in alpha cells is in good agreement to those reported for L-type calcium channels in beta cells. This finding is strongly relevant since both, L-type and N-type calcium channels, play a main role in insulin and glucagon secretion, respectively

Evaluation of Groundwater Storage Monitoring with the GRACE Satellite: Case Study High Plains Aquifer, Central United States

Water scarcity is a critical issue in semiarid regions; however, regional groundwater monitoring is extremely limited. This study evaluates the ability of the GRACE satellites to monitor groundwater storage in the semiarid High Plains aquifer, United States (450,000 km2 area), which is subjected to intense irrigation. GRACE-derived terrestrial water storage (TWS) is highly correlated with the sum of soil moisture (SM) and groundwater storage (GWS) (R = 0.96 for in situ measured SM from 78 stations and R = 0.95 for simulated SM with the Noah land surface model with root-mean-square difference of 38 mm and 36 mm, respectively). Correlation between seasonal GWS changes calculated from GRACE TWS minus SM and measured GWS (∼1000 wells per season) is also high (R = 0.73 for in situ SM and R = 0.72 for simulated SM). Variability in SM is mostly restricted to the upper 2 m of the soil. Monitored SM compared favorably with simulated SM (R = 0.82). Study results show the potential for using GRACE gravity measurements to monitor TWS and GWS over large semiarid regions subjected to intense irrigation

Functional and Psychological Characteristics of Belgian Men with Premature Ejaculation and Their Partners

Physiological, behavioral, cognitive, and emotional factors are generally acknowledged to play a role in premature ejaculation (PE). However, the nature and the extent of their etiological impact remain largely imprecise. The present study examined functional and psychometric dynamics at work in a PE population. A total of 461 men with PE and 80 partners completed an online questionnaire. The main outcome measures were self-reported ejaculatory latency time, the feeling of control upon ejaculation, sexual satisfaction, distress related to PE, trait anxiety (STAI-B), sexual cognitions (SIQ), social anxiety (LSAS and SISST), and personality traits (TCI-R). In our sample, the median latency time to ejaculation was between 1 and 2 minutes. Sexual satisfaction and distress correlated more strongly with the feeling of control than with the self-reported latency time. Men experienced more distress and dissatisfaction related to PE than did their partners while overestimating their partners’ distress and dissatisfaction. PE participants’ scores differed significantly, albeit slightly, from STAI-B, SIQ, LSAS, and SISST norms. The differences were negligible on TCI-R. Some differences became stronger when subtypes were considered. Participants combining generalized and lifelong PE with self-reported latency times of < 30 sec reported lower sexual satisfaction and control, higher distress, higher social anxiety, and harm avoidance (TCI-R/HA) scores. By contrast, the situational subtype of PE was found to be characterized by a higher level of satisfaction, a greater feeling of control, less distress, and higher trait anxiety scores. However, the trends remained statistically discrete.BibliothE