Contribution of the kinetics of G protein dissociation to the characteristic modifications of N-type calcium channel activity

Direct G protein inhibition of N-type calcium channels is recognized by characteristic biophysical modifications. In this study, we quantify and simulate the importance of G protein dissociation on the phenotype of G protein-regulated whole-cell currents. Based on the observation that the voltage-dependence of the time constant of recovery from G protein inhibition is correlated with the voltage-dependence of channel opening, we depict all G protein effects by a simple kinetic scheme. All landmark modifications in calcium currents, except inhibition, can be successfully described using three simple biophysical parameters (extent of block, extent of recovery, and time constant of recovery). Modifications of these parameters by auxiliary beta subunits are at the origin of differences in N-type channel regulation by G proteins. The simulation data illustrate that channel reluctance can occur as the result of an experimental bias linked to the variable extent of G protein dissociation when peak currents are measured at various membrane potentials. To produce alterations in channel kinetics, the two most important parameters are the extents of initial block and recovery. These data emphasize the contribution of the degree and kinetics of G protein dissociation in the modification of N-type currents

Disruption of the IS6-AID Linker Affects Voltage-gated Calcium Channel Inactivation and Facilitation

Two processes dominate voltage-gated calcium channel (CaV) inactivation: voltage-dependent inactivation (VDI) and calcium-dependent inactivation (CDI). The CaVβ/CaVα1-I-II loop and Ca2+/calmodulin (CaM)/CaVα1–C-terminal tail complexes have been shown to modulate each, respectively. Nevertheless, how each complex couples to the pore and whether each affects inactivation independently have remained unresolved. Here, we demonstrate that the IS6–α-interaction domain (AID) linker provides a rigid connection between the pore and CaVβ/I-II loop complex by showing that IS6-AID linker polyglycine mutations accelerate CaV1.2 (L-type) and CaV2.1 (P/Q-type) VDI. Remarkably, mutations that either break the rigid IS6-AID linker connection or disrupt CaVβ/I-II association sharply decelerate CDI and reduce a second Ca2+/CaM/CaVα1–C-terminal–mediated process known as calcium-dependent facilitation. Collectively, the data strongly suggest that components traditionally associated solely with VDI, CaVβ and the IS6-AID linker, are essential for calcium-dependent modulation, and that both CaVβ-dependent and CaM-dependent components couple to the pore by a common mechanism requiring CaVβ and an intact IS6-AID linker

Characterization of calcium-dependent potassium channels in antennal receptor neurones of Locusta migratoria

Wegener J, Tareilus E, Breer H. Characterization of calcium-dependent potassium channels in antennal receptor neurones of Locusta migratoria. Journal of Insect Physiology. 1992;38(4):237-248.Antennal receptor neurones from Locusta migratoria were identified by their bipolar morphology and their immunoreactivity with anti-horseradish-peroxidase antibodies. Using patch clamp techniques, an ion channel displaying a high conductance (180 ± 5 pS) and a strong selectivity for potassium ions was detected in somata membranes from these neurones. The channel activity was regulated by intracellular calcium concentrations and by membrane voltage. Intracellular ATP (5 mM) was shown to inhibit channel activity. This channel may be involved in signal transduction of antennal olfactory neurones by controlling their electrical activity

Olfactory signalling in antennal receptor neurones of the locust (Locusta migratoria)

Wegener J, Boekhoff I, Tareilus E, Breer H. Olfactory signalling in antennal receptor neurones of the locust (Locusta migratoria). Journal of Insect Physiology. 1993;39(2):153-163

Novel design for a coreless printed circuit board transformer realizing high bandwidth and coupling

Rogowski coils offer galvanic isolation and can measure alternating currents with a high bandwidth. Coreless printed circuit board (PCB) transformers have been used as an alternative to limit the additional stray inductance if a Rogowski coil can not be attached to the circuit. A new PCB transformer layout is proposed to reduce cost, decrease additional stray inductance, increase the bandwidth of current measurements and simplify the integration into existing designs

Modulators of human epithelial sodium channels (hENaC)

An assay method for the isolation of compounds that alter the human ENaC epithelial ion channel activity comprising: (i) preparing an expression system comprising human a -, b -, and q -subunits; (ii) adding a test compound to the expression system and: (iii) determining if there is a change in hENaC ion channel activity resulting from the addition of the test compound. Also claimed is a gene cassette under the control of a promoter and a transfer vector both comprising the three subunits above

Structures and functions of calcium channel beta subunits

Calcium channel beta subunits have profound effects on how alpha(1) subunits perform. In this article we summarize our present knowledge of the primary structures of beta subunits as deduced from cDNAs and illustrate their different properties. Upon co-expression with alpha(1) subunits, the effects of beta subunits vary somewhat between L-type and non-L-type channels mostly because the two types of channels have different responses to voltage which are affected by beta subunits, such as lone-lasting prepulse facilitation of alpha(1C) (absent in alpha(1E)) and inhibition by G protein beta gamma dimer of alpha(1E), absent in alpha(1C). One beta subunit, a brain beta 2a splice variant that is palmitoylated, has several effects not seen with any of the others, and these are due to palmitoylation. We also illustrate the finding that functional expression of alpha(1) in oocytes requires a beta subunit even if the final channel shows no evidence for its presence. We propose two structural models for Ca2+ channels to account for "alpha(1) alone" channels seen in cells with limited beta subunit expression. In one model, beta dissociates from the mature alpha(1) after proper folding and membrane insertion. Regulated channels seen upon co-expression of high levels of beta would then have subunit composition alpha(1)beta In the other model, the "chaperoning" beta remains associated with the mature channel and "alpha(1) alone" channels would in fact be alpha(1)beta channels. Upon co-expression of high levels of beta the regulated channels would have composition [alpha(1)beta]beta

Strategies to reduce sodium consumption : a food industry perspective

The global high prevalence of hypertension and cardiovascular disease has raised concerns regarding the sodium content of the foods which we consume. Over 75% of sodium intake in industrialized diets is likely to come from processed and restaurant foods. Therefore international authorities, such as the World Health Organisation, are encouraging the food industry to reduce sodium levels in their products. Significant sodium reduction is not without complications as salt plays an important role in taste, and in some products is needed also for preservation and processing. The most promising sodium reduction strategy is to adapt the preference of consumers for saltiness by reducing sodium in products in small steps. However, this is a time-consuming approach that needs to be applied industry-wide in order to be effective. Therefore the food industry is also investigating solutions that will maintain the same perceived salt intensity at lower sodium levels. Each of these has specific advantages, disadvantages, and time lines for implementation. Currently applied approaches are resulting in sodium reduction between 20-30%. Further reduction will require new technologies. Research into the physiology of taste perception and salt receptors is an emerging area of science that is needed in order to achieve larger sodium reductions.<br /