Regulation Of Calcium Channel Activity Research Articles

GENOME-WIDE ASSOCIATION META-ANALYSIS OF PHYSICAL PERFORMANCE IN OLDER ADULTS

Abstract Although measures of physical function such as walking speed and time to complete chair-rises are highly heritable, the genetic architecture underlying these phenotypes remains poorly defined. To identify potentially novel genes and pathways underlying physical performance in older adults, we conducted a genome-wide association meta-analysis of the short physical performance battery (SPPB) (Score 0-12) and one of its components, chair-rise time (seconds) in 24,033 Caucasian adults aged 60+ from 13 cohorts (mean cohort age 66.2 ± 5.3 to 84.3 ± 4.1 years; 56.5% women). Cohorts had a genome wide scan imputed to either the Haplotype Reference Consortium or Trans-Omics for Precision Medicine imputation panels. Single nucleotide polymorphism (SNPs) with a minor allele frequency ≥0.1% and imputation quality score ≥0.7 were included (range 7.5-10.5 million per cohort). Analyses were adjusted for age, sex, height, and population substructure. Meta-analysis was performed using a fixed-effects model. Although no genome-wide significant loci were identified, 67 and 60 suggestive loci (p< 5*10-5) were detected for SPPB score and chair-rises time, respectively. Pathway-based analyses indicated significant enrichment of genes affecting negative regulation of calcium channel activity (Bonferroni corrected p-value < 0.05). Sex-stratified gene-based analyses identified clathrin vesicle-associated sec14 protein 1 (CLVS1), significantly associated with chair-rise time in women (p= -1.5*10-7). CLVS1 is highly expressed in the cerebellum, which is involved in postural and motor function control. A larger sample size is needed to confirm and extend our findings, but our results potentially implicate a novel pathway and locus for physical performance in older women.

ATHK1 acts downstream of hydrogen peroxide to mediate ABA signaling through regulation of calcium channel activity in Arabidopsis guard cells

Plants gradually develop their ability to tolerate environmental water deficit as part of the evolutionary process. Abscisic acid (ABA) plays a critical role during drought and osmotic stress. Several histidine protein kinases are regarded as osmotic sensors or regulators in the adaptive response of plants to water deficit. In this study, we report that ATHK1, which was previously shown to function as an osmotic regulator, is involved in ABA-induced stomatal signaling in Arabidopsis. Mutants null for ATHK1 expression were unable to transmit normal ABA responses in guard cells, including inducing stomatal closure, producing hydrogen peroxide and activating calcium influx. Moreover, patch clamp and confocal analysis demonstrated that ATHK1 may function downstream of hydrogen peroxide in ABA-induced stomatal closure, by regulating calcium channel activity and calcium oscillation in Arabidopsis guard cells.

New Approaches to Pathogenesis and Management of Hypertension

New Approaches to Pathogenesis and Management of Hypertension

Calcium Channels Brought Inside by Opioid-Like Receptor

Nociceptin is an endogenous pain-alleviating peptide that binds to the receptor ORL1, which is structurally similar to opioid receptors. ORL1 was recently found to interact directly with N-type calcium channels, resulting in tonic, agonist-independent inhibition. Altier et al. extend these observations and report that extended exposure to nociceptin stimulated the internalization of both ORL1 and N-type calcium channels, thereby decreasing calcium signaling. Initial experiments performed with transfected cells--imaging analysis and biochemical assays for cell surface versus internal pools of the receptor and channel--indicated that prolonged nociceptin exposure of cells expressing tagged forms ORL1 and Cav2.2 resulted in their internalization and their accumulation in acidic, lysosomal, and endosomal structures. The internalization was specific for the Cav2.2 channel and the ORL1 receptor and did not occur if ORL1 was coexpressed with other types of channels or if Cav2.2 was expressed with other opioid receptors or the G protein-coupled receptor angiotensin receptor 1 (ATR1). Analysis of dorsal root ganglion (DRG) neurons indicated that nociceptin treatment promoted the redistribution of N-type calcium channels in a subset of neurons (presumably the 10% in which ORL1 was present) from the cell surface to punctate internal structures. In the transfected cells, N-type channel current density was decreased by prolonged exposure to nociceptin. In cultured DRG neurons, one population of cells exhibited a pronounced inhibition of calcium signal after 30-minute nociceptin exposure. The abundance of the pool of cells that showed inhibition was the same as the abundance of ORL1-positive cells in the culture, which is consistent with the inhibited cells being the ones expressing ORL1. This cointernalization represents a novel mechanism for regulation of calcium channel activity and has implications for pain management and understanding the molecular mechanisms underlying tolerance to opioid pain relievers. C. Altier, H. Khosravani, R. M. Evans, S. Hameed, J. B. Peloquin, B. A. Vartian, L. Chen, A. M. Beedle, S. S. G. Ferguson, A. Mezghrani, S. J. Dubel, E. Bourinet, J. E. McRory, G. W. Zamponi, ORL1 receptor-mediated internalization of N-type calcium channels. Nat. Neurosci. 9 , 31-40 (2005). [PubMed]

Regulation of Calcium Channel Activity by Lipid Domain Formation in Planar Lipid Bilayers

The sarcoplasmic reticulum channel (ryanodine receptor) from cardiac myocytes was reconstituted into planar lipid bilayers consisting of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) and 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) in varying ratios. The channel activity parameters, i.e., open probability and average open time and its resolved short and long components, were determined as a function of POPE mole fraction ( X PE) at 22.4°C. Interestingly, all of these parameters exhibited a narrow and pronounced peak at X PE ≈ 0.80. Differential scanning calorimetric measurements on POPE/POPC liposomes with increasing X PE indicated that the lipid bilayer enters a composition-driven transition from the liquid-crystalline state to the gel state at 22.4°C when X PE approaches 0.80. Thus, the peaking of the reconstituted channel activity at X PE ≈ 0.80 in the planar bilayer could result from the appearance of gel/liquid-crystalline domain boundaries at this POPE content. Lipid packing at domain boundaries is known to be looser as compared to the homogenous gel or liquid-crystalline state. We propose that the attractive potential of packing defects at lipid domain boundaries and entropic excluded-volume effects could result in the direct interactions of the transmembrane region of the channel protein with the lipid-packing defects at the lipid/protein interface, which could thus provide a favorable environment for the open state of the protein. The present findings indicate that the activity of the sarcoplasmic reticulum calcium channel could be modulated by lipid domain formation upon slight changes in membrane lipid composition in vivo.

Regulation of presynaptic calcium channels by synaptic proteins.

Calcium entry into nerve termini via voltage gated calcium channels is an essential step in neurotransmission. Consequently, second messenger regulation of calcium channel activity modulates synaptic activity. It has been suggested that calcium channels must physically couple to the release machinery, and a physical interaction between a synaptic protein interaction (synprint) site contained within mammalian presynaptic calcium channels and synaptic proteins such as syntaxin 1, SNAP-25, and synaptotagmin has been demonstrated. Interestingly, synaptic calcium channels in invertebrates lack this region. In invertebrates, synaptic transmission is instead dependent on a presynaptic calcium channel splice variant that can physically associate with the adaptor proteins Mint-1 and CASK. We suggest that in the absence of a synprint region, these proteins may localize calcium channels to the synaptic release machinery. The interactions between synaptic proteins and mammalian N-type calcium channels serves to regulate calcium channel activity directly, as well as indirectly by altering second messenger regulation of the channels. This provides for a feedback mechanism that allows the fine-tuning of calcium channel activity during various steps in neurotransmitter release. This does not occur with invertebrate synaptic calcium channel homologs, suggesting that the regulation of calcium channel activity by synaptic proteins is a mechanism unique to vertebrates.

Expression of cGMP-dependent Protein Kinase in Human Atrium

We have shown that cGMP-dependent protein kinase (PKG) mediates stimulation of L-type calcium current by cGMP in rabbit atrial myocytes. The human atrium may have similar PKG-dependent regulation of calcium current. To elucidate the significance of PKG in cardiac function, we have isolated human PKG type I α cDNA (+1 to 2016), determined the nucleotide sequence and analyzed specific expression of PKG in human atrium. We obtained full-length cDNA of PKG type Iα from human atrial RNA using reverse transcriptase-polymerase chain reaction (RT-PCR). The coding region of human cardiac PKG I α showed 99.9% homology to previously published human PKG I α except for base No. 1983. At this position G was substituted for T and this resulted in an amino acid substitution from Leu649to Phe649. The cloned PKG I α cDNA was expressed in COS cells and the expressed PKG showed cGMP-stimulated PKG enzyme activity and immunoreactivity. Ribonuclease protection assay, Western blot analysis, and PKG enzyme activity assays in homogenates from human atrial tissue demonstrated the presence of PKG mRNA and protein in human atrial tissue. Immunofluorescence staining confirmed that PKG is highly expressed in human atrial myocytes. These findings suggest that PKG is highly expressed in human atrium and that PKG-dependent phosphorylation may be important in regulation of calcium channel activity in human atrial myocytes.

Role of calcineurin in regulation of high voltage-activated calcium channel activity

In the Review, personal data of the Author and the data of other experimenters on calcium/calmodulin-dependent protein phosphatase-2B (calcineurin) are summarized and analyzed; the role of this enzyme in regulation of the calcium channel activity in the membrane of excitable cells is discussed. A two-phase mechanism of Ca-dependent suppression of the activity of Ca channels in the molluscan neurons is described in details. Special attention is paid to the analysis of changes in the activity of Ca channels in the transfected hybrid cells overexpressing calcineurin.

Dynorphin A and cAMP-dependent protein kinase independently regulate neuronal calcium currents.

The kappa-selective opioid peptide dynorphin A (DYN) inhibits neuronal adenylate cyclase activity and reduces neuronal voltage-dependent calcium currents. It is not yet known, however, whether the regulation of calcium channel activity is dependent on or independent of the adenylate cyclase/cAMP system. We used the whole-cell variation of the patch clamp technique to show that DYN reversibly reduced, in a naloxone-sensitive manner, calcium currents in acutely dissociated rat nodose ganglion neurons. DYN slowed the rate of current activation and had a greater effect on currents evoked from relatively negative holding potentials. These actions were mimicked by guanosine 5'-[gamma-thio]triphosphate, which activates GTP-binding proteins (G proteins), and were blocked by pretreatment with pertussis toxin, which inactivates Gi- and Go-type G proteins. In contrast, calcium currents recorded in the presence of the catalytic subunit of the cAMP-dependent protein kinase (AK-C), included in the recording pipette, increased in magnitude throughout the recording. DYN was applied to neurons before and after the effect of AK-C became apparent; the reduction of calcium currents by DYN was greater in the presence of AK-C than in its absence. We conclude that the acute reduction of neuronal calcium currents by DYN occurred by means of activation of pertussis toxin-sensitive Gi- or Go-type G proteins. The persistence of the action of DYN in the presence of AK-C indicates, however, that this effect was independent of a reduction of the activity of the adenylate cyclase/cAMP system and suggests in addition that phosphorylated channels may be preferentially inhibited by DYN.

Photoaffinity labelling and phosphorylation of a 165 kilodalton peptide associated with dihydropyridine and phenylalkylamine-sensitive calcium channels

Partially purified fractions of dihydropyridine and phenylalkylamine receptors associated with voltage-dependent calcium channels in rabbit skeletal muscle were found to contain two glycopeptides of similar molecular weight. A peptide of approximately 165 kDa was photoaffinity labelled with an arylazido-phenylalkylamine Ca channel inhibitor and also was phosphorylated with cAMP-dependent protein kinase. Another peptide of 170 kDa could be distinguished from the 165 kDa peptide by peptide mapping and differences in electrophoretic mobility. The results suggest that the 165 kDa peptide contains the sites responsible for regulation of calcium channel activity by calcium channel inhibitors as well as by neurotransmitters that regulate its activity in a cAMP-dependent manner.