Lang, Florian, Gillian L. Busch, Markus Ritter, Harald Volkl, Siegfried Waldegger, Erich Gulbins, and Dieter Haussinger. Functional Significance of Cell Volume Regulatory Mechanisms. Physiol. Rev. ...

Functional Significance of Cell Volume Regulatory Mechanisms

A new type of self-assembling peptide (sapeptide) scaffolds that serve as substrates for neurite outgrowth and synapse formation is described. These peptide-based scaffolds are amenable to molecular design by using chemical or biotechnological syntheses. They can be tailored to a variety of applications. The sapeptide scaffolds are formed through the spontaneous assembly of ionic self-complementary β-sheet oligopeptides under physiological conditions, producing a hydrogel material. The scaffolds can support neuronal cell attachment and differentiation as well as extensive neurite outgrowth. Furthermore, they are permissive substrates for functional synapse formation between the attached neurons. That primary rat neurons form active synapses on such scaffold surfaces in situ suggests these scaffolds could be useful for tissue engineering applications. The buoyant sapeptide scaffolds with attached cells in culture can be transported readily from one environment to another. Furthermore, these peptides did not elicit a measurable immune response or tissue inflammation when introduced into animals. These biological materials created through molecular design and self assembly may be developed as a biologically compatible scaffold for tissue repair and tissue engineering.

https://www.pnas.org/content/pnas/97/12/6728.full.pdf

Extensive neurite outgrowth and active synapse formation on self-assembling peptide scaffolds

Voltage-dependent ion channels contain voltage sensors that allow them to switch between nonconductive and conductive states over the narrow range of a few hundredths of a volt. We investigated the mechanism by which these channels sense cell membrane voltage by determining the x-ray crystal structure of a mammalian Shaker family potassium ion (K+) channel. The voltage-dependent K+ channel Kv1.2 grew three-dimensional crystals, with an internal arrangement that left the voltage sensors in an apparently native conformation, allowing us to reach three important conclusions. First, the voltage sensors are essentially independent domains inside the membrane. Second, they perform mechanical work on the pore through the S4-S5 linker helices, which are positioned to constrict or dilate the S6 inner helices of the pore. Third, in the open conformation, two of the four conserved Arg residues on S4 are on a lipid-facing surface and two are buried in the voltage sensor. The structure offers a simple picture of how membrane voltage influences the open probability of the channel.

/pdf/voltage-sensor-of-kv1-2-structural-basis-of-2igmz97c25.pdf

Voltage Sensor of Kv1.2: Structural Basis of Electromechanical Coupling

Two-pore domain K+ (K2P) channels give rise to leak (also called background) K+ currents. The well-known role of background K+ currents is to stabilize the negative resting membrane potential and c...

/pdf/molecular-background-of-leak-k-currents-two-pore-domain-3xd1km54it.pdf

Molecular Background of Leak K+ Currents: Two-Pore Domain Potassium Channels

Teleost fishes represent a highly diverse group consisting of more than 20,000 species living across all aquatic environments. This group has significant economical, societal and environmental impacts, yet research efforts have concentrated primarily on salmonid and cyprinid species. This review examines carbohydrate/glucose metabolism and its regulation in these model species including the role of hormones and diet. Over the past decade, molecular tools have been used to address some of the downstream components of these processes and these are incorporated to better understand the roles played by carbohydrates and their regulatory paths. Glucose metabolism remains a contentious area as many fish species are traditionally considered glucose intolerant and, therefore, one might expect that the use and storage of glucose would be considered of minor importance. However, the actual picture is not so clear since the apparent intolerance of fish to carbohydrates is not evident in herbivorous and omnivorous species and even in carnivorous species, glucose is important for specific tissues and/or for specific activities. Thus, our aim is to up-date carbohydrate metabolism in fish, placing it to the context of these new experimental tools and its relationship to dietary intake. Finally, we suggest that new research directions ultimately will lead to a better understanding of these processes.

Glucose metabolism in fish: a review

Two-pore domain K+ channels-molecular sensors.

TASK-1 and -2 are members of the two-pore domain potassium (K+) channel family and are sensitive to changes in extracellular pH. The effects of mutating charged, extracellular-facing residues in TASK-1 and –2 were studied in Xenopus oocytes by two-electrode voltage clamp. Hydrogen ion block was independent of voltage with K
d values of 149±17.9 nM [H+] (n=6) and 5.76±1.23 nM [H+] (n=7) for TASK-1 and -2, respectively. Compared to wild-type TASK-1, H72N, H98N, H98D and K210N displayed significant shifts in their K
d values for hydrogen ion block ([H+]; 110±9.80 nM, 737±170 nM, 321±85.9 nM and 267±9.92 nM, respectively, n=6 each, P<0.05). Although significantly reducing its pH sensitivity, mutation of H98 in TASK-1 did not abolish pH sensitivity; this implies that H98 is not the only residue or domain involved in pH sensing of TASK-1. TASK-2 does not possess a histidine residue at the homologous position. However, the inclusion of such a residue failed to produce the expected increase in pH sensitivity; instead, a slight decrease was observed. Despite their structural homology and common sensitivity to pH, the TASK family of K+ channels apparently has diverse pH-sensing mechanisms.

Determinants of pH sensing in the two-pore domain K(+) channels TASK-1 and -2.

1. The whole-cell patch clamp technique was used to investigate Cl- currents in single proximal tubule cells isolated from kidneys of Rana temporaria. 2. Immediately following establishment of the whole-cell clamp, the Cl- conductance (gCl) of the cells was low. However, with 2 mM ATP in the pipette there was a time-dependent activation of gCl. Such activation was inhibited when the bath contained a hypertonic Ringer solution. 3. The Cl- conductance was not directly dependent on cell volume; gCl increased with hypotonic shock and decreased with hypertonic shock, but only in the presence of ATP. 4. Activation of gCl by ATP was dependent on extracellular Ca2+; however, the conductance was not directly Ca2+ sensitive. Activation was inhibited by Gd3+, which also had a direct inhibitory action on gCl. 5. Inhibition of protein kinase C (PKC), by 10 microM PKC pseudo-substrate (PKC-ps), completely abolished the ATP-dependent activation of gCl, while stimulation of PKC, by the PKC activator 4 beta-phorbol 12-myristate, 13-acetate (PMA), increased the degree of activation typically observed with ATP. 6. We propose that gCl is activated by PKC-mediated phosphorylation and plays a role in volume regulation of the cells.

Role of cell volume and protein kinase C in regulation of a Cl‐ conductance in single proximal tubule cells of Rana temporaria.

Evidence for Intersubunit Interactions between S4 and S5 Transmembrane Segments of the Shaker Potassium Channel

We have investigated the expression of TASK-1, a pH-sensitive, twin-pore domain K+channel in the rat heart. A mammalian cell line of Chinese hamster ovary cells (CHO), transfected with a plasmid co...

https://www.physiology.org/doi/pdf/10.1152/ajpheart.00963.2001

Expression of TASK-1, a pH-sensitive twin-pore domain K channel, in rat myocytes

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