Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Transient Receptor Potential Channels”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
PubMed2006

Capsaicin inhibits catecholamine secretion and synthesis by blocking Na+ and Ca2+ influx through a vanilloid receptor-independent pathway in bovine adrenal medullary cells.

We report here the effects of capsaicin, a flavoring ingredient in the hot pepper Capsicum family, on catecholamine secretion and synthesis in cultured bovine adrenal medullary cells. Capsaicin inhibited catecholamine secretion (IC(50)=9.5, 11.8, and 62 microM) stimulated by carbachol, an agonist of the nicotinic acetylcholine receptor, by veratridine, an activator of voltage-dependent Na(+) channels, and by high K(+), an activator of voltage-dependent Ca(2+) channels, respectively. Capsaicin also suppressed carbachol-induced (22)Na(+) influx (IC(50)=5.0 microM) and (45)Ca(2+) influx (IC(50)=24.4 muM), veratridine-induced (22)Na(+) influx (IC(50)=2.4 microM) and (45)Ca(2+) influx (IC(50)=1.1 microM), and high K(+)-induced (45)Ca(2+) influx (IC(50)=5.8 microM). The reduction in catecholamine secretion caused by capsaicin was not overcome by increasing the concentration of carbachol. Furthermore, capsazepine (10 microM), a competitive antagonist for the transient receptor potential vanilloid 1, and ruthenium red (30 microM), a nonselective cation channel antagonist, did not block the inhibition by capsaicin of catecholamine secretion. Capsaicin also suppressed both basal and carbachol-stimulated (14)C-catecholamine synthesis (IC(50)=10.6 and 26.4 microM, respectively) from [(14)C] tyrosine but not from L: -3, 4-dihydroxyphenyl [3-(14)C] alanine ([(14)C] DOPA) as well as tyrosine hydroxylase activity (IC(50)=8.4 and 39.0 microM, respectively). The present findings suggest that capsaicin inhibits catecholamine secretion and synthesis via suppression of Na(+) and Ca(2+) influx through a vanilloid receptor-independent pathway.

Adrenal Medulla↗
PubMed2004

TRPC4 forms store-operated Ca2+ channels in mouse mesangial cells.

Studies were performed to identify the molecular component responsible for store-operated Ca(2+) entry in murine mesangial cells (MMC). Because the canonical transient receptor potential (TRPC) family of proteins was previously shown to comprise Ca(2+)-selective and -nonselective cation channels in a variety of cells, we screened TRPC1-TRPC7 with the use of molecular methods and the fura 2 method to determine their participation as components of the mesangial store-operated Ca(2+) (SOC) channel. Using TRPC-specific primers and RT-PCR, we found that cultured MMC contained mRNA for TRPC1 and TRPC4 but not for TRPC2, TRPC3, TRPC5, TRPC6, and TRPC7. Immunocytochemical staining of MMC revealed predominantly cytoplasmic expression of TRPC1 and plasmalemmal expression of TRPC4. The role of TRPC4 in SOC was determined with TRPC4 antisense and fura 2 ratiometric measurements of intracellular Ca(2+) concentration ([Ca(2+)](i)). SOC was measured as the increase in [Ca(2+)](i) after extracellular Ca(2+) was increased from <10 nM to 1 mM in the continued presence of thapsigargin. We found that TRPC4 antisense, which reduced plasmalemmal expression of TRPC4, inhibited SOC by 83%. Incubation with scrambled TRPC4 oligonucleotides did not affect SOC. Immunohistochemical staining identified expressed TRPC4 in the glomeruli of mouse renal sections. The results of RT-PCR performed to distinguish between TRPC4-alpha and TRPC4-beta were consistent with expression of both isoforms in brain but with only TRPC4-alpha expression in MMC. These studies show that TRPC4-alpha may form the homotetrameric SOC in mouse mesangial cells.

Animals↗
PubMed2007

TRPC3: a multifunctional, pore-forming signalling molecule.

TRPC3 represents one of the first identified mammalian relatives of the Drosophila trp gene product. Despite intensive biochemical and biophysical characterization as well as numerous attempts to uncover its physiological role in native cell systems, this channel protein still represents one of the most enigmatic members of the transient receptor potential (TRP) superfamily. TRPC3 is significantly expressed in brain and heart and likely to play a role in both non-excitable as well as excitable cells, being potentially involved in a wide spectrum of Ca2+ signalling mechanisms. Its ability to associate with a variety of partner proteins apparently enables TRPC3 to form different cation channels in native cells. TRPC3 cation channels display unique gating and regulatory properties that allow for recognition and integration of multiple input stimuli including lipid mediators and cellular Ca2+ gradients as well as redox signals. The physiological/pathophysiological functions of this highly versatile cation channel protein are as yet barely delineated. Here we summarize current knowledge on properties and possible signalling functions of TRPC3 and discuss the potential biological relevance of this signalling molecule.

Animals↗
PubMed2003

[Ionic mechanisms underlying the regulation of cell proliferation, differentiation and death].

Ion channels and transporters act as major components that regulate membrane excitability in neurons, muscles, and some secretory glands, but may also contribute to the regulation of proliferation, differentiation, and death in a greater variety of cells including non-excitable ones. The molecular basis of ionic mechanisms underlying the later regulation has been partly identified in the last several years and is a hot issue now. In this short review, some of the molecular mechanisms underlying these regulations and novel compounds acting on the mechanisms were introduced as exciting topics in this area. Several types of transient receptor potential (TRP), identified as Ca(2+)-permeable, non-selective cation channels, may play obligatory roles in functional complexes, which regulate multiple signal transduction pathways triggering proliferation, differentiation, or death of many cell types. In addition, the relation between Cl(-) pump activity and the induction of beta-amyloid protein toxicity for neuronal cell death in Alzheimer disease was described. Unique functions of H(+) channel and pump in osteoclasts in bone mineral homeostasis and remodeling were also discussed. Finally, topics about activation of specific types of Cl(-) channels and K(+) channels, which are responsible for the induction of apoptosis or proliferation in several types of cells, were introduced.

Alzheimer Disease↗
PubMed2005

Proteomic analysis of TRPC5- and TRPC6-binding partners reveals interaction with the plasmalemmal Na(+)/K(+)-ATPase.

Mammalian transient receptor potential canonical (TRPC) genes encode a family of nonselective cation channels that are activated following stimulation of G-protein-coupled membrane receptors linked to phospholipase C. In Drosophila photoreceptor cells, TRP channels are found in large, multimolecular signaling complexes in association with the PDZ-containing scaffolding protein, INAD. A similar mammalian TRPC "signalplex" has been proposed, but has yet to be defined. In the present study, affinity-purified polyclonal antibodies against TRPC5 and TRPC6 were used to immunoprecipitate signalplex components from rat brain lysates. Immunoprecipitated proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, digested with trypsin, and sequenced by mass spectrometry. Proteins identified in the immunoprecipitates included cytoskeletal proteins spectrin, myosin, actin, drebrin, tubulin, and neurabin; endocytic vesicle-associated proteins clathrin, dynamin and AP-2; and the plasmalemmal Na(+)/K(+)-ATPase (NKA) pump. Several of these interactions were confirmed by reciprocal immunoprecipitation followed by Western blot analysis. In lysates from rat kidney, TRPC6, but not TRPC3, was found to coimmunoprecipitate with the NKA pump. Likewise, TRPC6, stably expressed in human embryonic kidney (HEK) cells, coimmunoprecipitated with endogenous NKA and colocalized with the pump to the plasmalemma when examined by immunofluorescence microscopy. Cell surface biotinylation experiments in intact HEK cells, confirmed that both the Na(+) pump and TRPC6 were present in the surface membrane and appeared to interact. Lastly, TRPC6 coimmunoprecipitated with the NKA pump when the proteins were coexpressed in Spodoptera frugiperda insect cells using recombinant baculoviruses. These observations suggest that TRPC6 and the Na(+) pump are part of a functional complex that may be involved in ion transport and homeostasis in both the brain and kidney.

Animals↗
PubMed2005

Characterization of human and mouse TRPM2 genes: identification of a novel N-terminal truncated protein specifically expressed in human striatum.

Transient receptor potential melastatin 2 (TRPM2) is a calcium-permeable cation channel activated by ADP-ribose or reactive oxygen species. In human, a major transcript of 6.5 kb is expressed in various tissues, whereas a minor transcript of 5.5 kb is detected only in striatum (caudate nucleus and putamen). We found that the 5.5-kb shorter transcript is transcribed from the intron 4 of the TRPM2 gene and encodes the striatum short form protein (SSF-TRPM2) with 1289 amino acid residues as compared to the long form protein (LF-TRPM2), in which the N-terminal 214 amino acid residues are removed. The SSF-TRPM2 protein still maintained H2(O2)-induced Ca2+ influx activity. In addition, we found that the major transcripts in human and mouse start from a novel 5' non-coding exon; however, we could not detect any striatum short transcript in mouse brain. These new findings are invaluable to further study the regulation of TRPM2 gene expression and to examine the possible involvement of the TRPM2 gene in the pathophysiology of bipolar disorder.

Amino Acid Sequence↗
PubMed2005

Defective skeletogenesis with kidney stone formation in dwarf zebrafish mutant for trpm7.

Development of the adult form requires coordinated growth and patterning of multiple traits in response to local gene activity as well as to global endocrine and physiological effectors. An excellent example of such coordination is the skeleton. Skeletal development depends on the differentiation and morphogenesis of multiple cell types to generate elements with distinct forms and functions throughout the body. We show that zebrafish touchtone/nutria mutants exhibit severe growth retardation and gross alterations in skeletal development in addition to embryonic melanophore and touch-response defects. These alterations include accelerated endochondral ossification but delayed intramembranous ossification, as well as skeletal deformities. We show that the touchtone/nutria phenotype results from mutations in trpm7, which encodes a transient receptor potential (TRP) family member that functions as both a cation channel and kinase. We find trpm7 expression in the mesonephric kidney and show that mutants develop kidney stones, indicating renal dysfunction. These results identify a requirement for trpm7 in growth and skeletogenesis and highlight the potential of forward genetic approaches to uncover physiological mechanisms contributing to the development of adult form.

Abnormalities, Multiple↗
PubMed2006

Modulation of human TRPV1 receptor activity by extracellular protons and host cell expression system.

The transient receptor potential vanilloid 1 (TRPV1) receptor is a ligand-gated cation channel that can be activated by capsaicin, heat, protons and cytosolic lipids. We compared activation of recombinant human TRPV1 receptors stably expressed in human 293 cells, derived from kidney embryonic cells, and in human 1321N1 cells, derived from brain astrocytes. Cellular influx of calcium was measured in response to acid, endovanilloids (N-arachidonoyl-dopamine, N-oleoyl-dopamine and anandamide), capsaicin and other traditional vanilloid agonists under normal (pH 7.4) and acidic (pH 6.7 and 6.0) assay conditions. The host cell expression system altered the agonist profile of endogenous TRPV1 receptor agonists without affecting the pharmacological profile of either exogenous TRPV1 receptor agonists or antagonists. Our data signify that the host cell expression system plays a modulatory role in TRPV1 receptor activity, and suggests that activation of native human TRPV1 receptors in vivo will be dependent on cell-specific regulatory factors/pathways.

Calcium↗
PubMed2005

A TRPM7 variant shows altered sensitivity to magnesium that may contribute to the pathogenesis of two Guamanian neurodegenerative disorders.

Guamanian amyotrophic lateral sclerosis (ALS-G) and parkinsonism dementia (PD-G) have been epidemiologically linked to an environment severely deficient in calcium (Ca2+) and magnesium (Mg2+). Transient receptor potential melastatin 7 (TRPM7) is a bifunctional protein containing both channel and kinase domains that has been proposed to be involved in the homeostatic regulation of intracellular Ca2+, Mg2+, and trace metal ion concentration. There is evidence that TRPM7 is constitutively active and that the number of available channels is dependent on intracellular free Mg2+ levels. We found a TRPM7 variant in a subset of ALS-G and PD-G patients that produces a protein with a missense mutation, T1482I. Recombinant T1482I TRPM7 exhibits the same kinase catalytic activity as WT TRPM7. However, heterologously expressed T1482I TRPM7 produces functional channels that show an increased sensitivity to inhibition by intracellular Mg2+. Because the incidence of ALS-G and PD-G has been associated with prolonged exposure to an environment severely deficient in Ca2+ and Mg2+, we propose that this variant TRPM7 allele confers a susceptibility genotype in such an environment. This study represents an initial attempt to address the important issue of gene-environment interactions in the etiology of these diseases.

Amino Acid Sequence↗
PubMed2004

Increased expression of TRPV1 receptor in dorsal root ganglia by acid insult of the rat gastric mucosa.

It is still unknown which receptors of peripheral sensory pathways encode and integrate an acid-induced nociceptive event in the gastric mucosa. The transient receptor potential vanilloid receptor 1 (TRPV1) and the acid-sensing ion channel 3 (ASIC3) are two nociception-related receptors. Here we investigated (i) to what extent these receptors are distributed in stomach-innervating neurons of dorsal root and nodose ganglia, using immunohistochemistry and retrograde tracing, and (ii) whether their expression is altered in response to a noxious acid challenge of the stomach. We also explored the presence of TRPV1 in the gastric enteric nervous system because of its possible expression by intrinsic sensory neurons. Most stomach-innervating neurons in nodose ganglia were immunoreactive for TRPV1 (80%) and ASIC3 (75%), these results being similar in the dorsal root ganglia (71 and 82%). RT-PCR and Western blotting were performed up to 6 h after oral application of 0.5 m HCl to conscious rats. TRPV1 protein was increased in dorsal root but not in nodose ganglia whereas TRPV1 and ASIC3 mRNAs remained unchanged. TRPV1 mRNA was detected in longitudinal muscle-myenteric plexus preparations of control stomachs and was not altered by the acid challenge. Combined vagotomy and ganglionectomy abolished expression of TRPV1, indicating that it may derive from an extrinsic source. In summary, noxious acid challenge of the stomach increased TRPV1 protein in spinal but not vagal or intrinsic sensory afferents. The TRPV1 receptor may be a key molecule in the transduction of acid-induced nociception of the gastric mucosa and a mediator of visceral hypersensitivity.

Acid Sensing Ion Channels↗
PubMed2005

TRPV1b, a functional human vanilloid receptor splice variant.

Transient receptor potential (TRP) genes encode a family of related ion-channel subunits. This family consists of cation-selective, calcium-permeable channels that include a group of vanilloid receptor channels (TRPV) implicated in pain and inflammation. These channels are activated by diverse stimuli, including capsaicin, lipids, membrane deformation, heat, and protons. Six members of the TRPV family have been identified that differ predominantly in their activation properties. However, in neurons, TRPV channels do not account for the observed diversity of responses to activators. By probing human and rat brain cDNA libraries to identify TRPV subunits, we identified a novel human TRPV1 RNA splice variant, TRPV1b, which forms functional ion channels that are activated by temperature (threshold, approximately 47 degrees C), but not by capsaicin or protons. Channels with similar activation properties were found in trigeminal ganglion neurons, suggesting that TRPV1b receptors are expressed in these cells and contribute to thermal nociception.

Amino Acid Sequence↗
PubMed2004

Identification of a tetramerization domain in the C terminus of the vanilloid receptor.

TRPV1 (transient receptor potential vanilloid receptor subtype 1) is a member of the TRP channel family gated by vanilloids, protons, and heat. Structurally, TRPV1 appears to be a tetramer formed by the assembly of four identical subunits around a central aqueous pore. The molecular determinants that govern its subunit oligomerization remain elusive. Here, we report the identification of a segment comprising 684Glu-721Arg (referred to as the TRP-like domain) in the C terminus of TRPV1 as an association domain (AD) of the protein. Purified recombinant C terminus of TRPV1 (TRPV1-C) formed discrete and stable multimers in vitro. Yeast two-hybrid and pull-down assays showed that self-association of the TRPV1-C is blocked when segment 684Glu-721Arg is deleted. Biochemical and immunological analysis indicate that removal of the AD from full-length TRPV1 monomers blocks the formation of stable heteromeric assemblies with wild-type TRPV1 subunits. Deletion of the AD in a poreless TRPV1 subunit suppressed its robust dominant-negative phenotype. Together, these findings are consistent with the tenet that the TRP-like domain in TRPV1 is a molecular determinant of the tetramerization of receptor subunits into functional channels. Our observations suggest that the homologous TRP domain in the TRP protein family may function as a general, evolutionary conserved AD involved in subunit multimerization.

Arginine↗
PubMed1996

INDO-1 measurements of absolute resting and light-induced Ca2+ concentration in Drosophila photoreceptors.

Absolute Ca2+ levels in dissociated Drosophila photoreceptors were measured using the ratiometric indicator dye INDO-1 loaded via patch pipettes, which simultaneously recorded whole-cell currents. In wild-type photoreceptors, the ultraviolet (UV) excitation light used to measure fluorescence elicited a massive Ca2+ influx that saturated the dye (>10 microM Ca2+), but lagged the electrical response by 2.8 msec. Resting Ca2+ levels in the dark, measured during the latent period before the response, averaged 160 nM in normal Ringer's (1.5 mM Ca2+). Ca2+ increases in response to weak illumination were estimated (1) by using a weak adapting stimulus before the UV excitation light and measuring Ca2+ during the latent period; and (2) by using ninaE mutants with greatly reduced rhodopsin levels. Ca2+ rose linearly as a function of the time integral of the light-sensitive current with a slope of 2.7 nM/pC. In the transient receptor potential (trp) mutant, which lacks a putative light-sensitive channel subunit, the slope was only 1.1 nM/pC, indicating a 2.5-fold reduction in the fractional Ca2+ current. From these data, it can also be estimated that >99% of the Ca2+ influx is effectively buffered by the cell. In Ca2+-free Ringer's, resting cytosolic Ca2+ was reduced (to 30-70 nM), but contrary to previous reports, significant light-induced increases (approximately 250 nM) could be elicited. This rise was reduced to <20 nM when extracellular Na+ was replaced with N-methyl-D-glucamine, suggesting that it could be attributed to Na+ influx altering the Na/Ca exchanger equilibrium. It is concluded that any light-induced release from internal stores amounts to <20 nM.

Animals↗
PubMed2001

Upregulated TRP and enhanced capacitative Ca(2+) entry in human pulmonary artery myocytes during proliferation.

A rise in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) due to Ca(2+) release from intracellular Ca(2+) stores and Ca(2+) influx through plasmalemmal Ca(2+) channels plays a critical role in mitogen-mediated cell growth. Depletion of intracellular Ca(2+) stores triggers capacitative Ca(2+) entry (CCE), a mechanism involved in maintaining Ca(2+) influx and refilling intracellular Ca(2+) stores. Transient receptor potential (TRP) genes have been demonstrated to encode the store-operated Ca(2+) channels that are activated by Ca(2+) store depletion. In this study, we examined whether CCE, activity of store-operated Ca(2+) channels, and human TRP1 (hTRP1) expression are essential in human pulmonary arterial smooth muscle cell (PASMC) proliferation. Chelation of extracellular Ca(2+) and depletion of intracellularly stored Ca(2+) inhibited PASMC growth in media containing serum and growth factors. Resting [Ca(2+)](cyt) as well as the increases in [Ca(2+)](cyt) due to Ca(2+) release and CCE were all significantly greater in proliferating PASMC than in growth-arrested cells. Consistently, whole cell inward currents activated by depletion of intracellular Ca(2+) stores and the mRNA level of hTRP1 were much greater in proliferating PASMC than in growth-arrested cells. These results suggest that elevated [Ca(2+)](cyt) and intracellularly stored [Ca(2+)] play an important role in pulmonary vascular smooth muscle cell growth. CCE, potentially via hTRP1-encoded Ca(2+)-permeable channels, may be an important mechanism required to maintain the elevated [Ca(2+)](cyt) and stored [Ca(2+)] in human PASMC during proliferation.

Blood Proteins↗
PubMed2006

Expression of transient receptor potential vanilloid 1 (TRPV1) and 2 (TRPV2) in human peripheral blood.

The vanilloid receptor family of cation channels includes the capsaicin-sensitive, proton- and heat-activated TRPV1 and noxious heat-activated TRPV2. The present study demonstrates both gene and protein expression of TRPV1 and TRPV2 in human peripheral blood cells (PBCs) using molecular and immunocytochemical techniques. Using reverse-transcription polymerase chain reaction (RT-PCR) and quantitative real-time RT-PCR (qRT-PCR), TRPV1 and TRPV2 mRNA was detected in mRNA isolated from human whole peripheral blood. Using qRT-PCR, TRPV2 mRNA was highly expressed in human whole blood isolates (9.33+/-1.19 x 10(4)copies per 10(6)copies of the housekeeping gene GAPDH), whereas TRPV1 message was detected at approximately 150-fold lower levels (638+/-121 copies per 10(6)copies GAPDH). At the protein level, TRPV1 and TRPV2 activity was determined immunocytochemically in a lymphocyte-enriched mononuclear cell preparation (83+/-2% lymphocytes). Cells were labelled with rabbit anti-TRPV1 or goat anti-TRPV2 (1:500) and subsequently labelled with goat Texas red- (TRPV1) or FITC-(TRPV2) conjugated secondary antibodies (1:1000). All cells demonstrated punctate TRPV1-immunoreactivity, which appeared to be on the plasma membrane and in the cytoplasm. In contrast, cells within subjects appeared to express the TRPV1 protein at varying intensities. TRPV2-immunoreactivity appeared diffuse. This is the first study to demonstrate the presence of both TRPV1 and TRPV2 in human peripheral lymphocytes. Further studies need to be undertaken in order to determine the role of TRPV channels in these cells.

Adult↗
PubMed1999

Mouse trp2, the homologue of the human trpc2 pseudogene, encodes mTrp2, a store depletion-activated capacitative Ca2+ entry channel.

Capacitative Ca2+ entry (CCE) is Ca2+ entering after stimulation of inositol 1,4,5-trisphosphate (IP3) formation and initiation of Ca2+ store depletion. One hallmark of CCE is that it can also be triggered merely by store depletion, as occurs after inhibition of internal Ca2+ pumps with thapsigargin. Evidence has accumulated in support of a role of transient receptor potential (Trp) proteins as structural subunits of a class of Ca2+-permeable cation channels activated by agonists that stimulate IP3 formation-very likely through a direct interaction between the IP3 receptor and a Trp subunit of the Ca2+ entry channel. The role of Trp's in Ca2+ entry triggered by store depletion alone is less clear. Only a few of the cloned Trp's appear to enhance this type of Ca2+ entry, and when they do, the effect requires special conditions to be observed, which native CCE does not. Here we report the full-length cDNA of mouse trp2, the homologue of the human trp2 pseudogene. Mouse Trp2 is shown to be readily activated not only after stimulation with an agonist but also by store depletion in the absence of an agonist. In contrast to other Trp proteins, Trp2-mediated Ca2+ entry activated by store depletion is seen under the same conditions that reveal endogenous store depletion-activated Ca2+ entry, i.e., classical CCE. The findings support the general hypothesis that Trp proteins are subunits of store- and receptor-operated Ca2+ channels.

Amino Acid Sequence↗
PubMed2006

Mechanism and functional significance of TRPC channel multimerization.

Ca(2+) signaling regulates many important physiological events within a diverse set of living organisms. In particular, sustained Ca(2+) signals play an important role in controlling cell proliferation, cell differentiation and the activation of immune cells. Two key elements for the generation of sustained Ca(2+) signals are store-operated and receptor-operated Ca(2+) channels that are activated downstream of phospholipase C (PLC) stimulation, in response to G-protein-coupled receptor or growth factor receptor stimulation. One goal of this review is to help clarify the role of canonical transient receptor potential (TRPC) proteins in the formation of native store-operated and native receptor-operated channels. Toward that end, data from studies of endogenous TRPC proteins will be reviewed in detail to highlight the strong case for the involvement of certain TRPC proteins in the formation of one subtype of store-operated channel, which exhibits a low Ca(2+)-selectivity, in contrast to the high Ca(2+)-selectivity exhibited by the CRAC subtype of store-operated channel. A second goal of this review is to highlight the growing body of evidence indicating that native store-operated and native receptor-operated channels are formed by the heteromultimerization of TRPC subunits. Furthermore, evidence will be provided to argue that some TRPC proteins are able to form multiple channel types.

Animals↗
PubMed2004

Facilitation of L-type Ca2+ channels in dendritic spines by activation of beta2 adrenergic receptors.

We studied the contribution of L-type Ca2+ channels to action potential-evoked Ca2+ influx in dendritic spines of CA1 pyramidal neurons and the modulation of these channels by the beta2 adrenergic receptor. Backpropagating action potentials (bAPs) (three at 50 Hz) were evoked by brief somatic current injections, and Ca2+ transients were recorded in proximal basal dendrites and associated spines. The R- and T-type Ca2+ channel blocker NiCl2 (100 microm) significantly reduced Ca2+ transients in both spines and their parent dendrites (approximately 50%), suggesting that these channels are the major source of bAP-evoked Ca2+ influx in these structures. The L-type Ca2+ channel blockers nimodipine and nifedipine (both 10 microm) reduced spine Ca2+ transients by approximately 10%, whereas the L-type Ca2+ channel activators FPL 64176 (2,5-dimethyl-4-[2-(phenylmethyl)benzoyl]-1H-pyrrole-3-carboxylic acid methylester) and Bay K 8644 ((+/-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)-phenyl]-3-pyridine carboxylic acid methyl ester) (both 10 microm) significantly enhanced the spine Ca2+ transients by 40-50%. Activation of beta2 adrenergic receptors with salbutamol (40 microm) or formoterol (5 microm) resulted in significant enhancements of the spine (40-50%) but not dendritic Ca2+ transients. This increase was prevented when L-type Ca2+ channels were blocked with nimodipine (10 microm) or when cAMP-dependent protein kinase A (PKA) was inhibited with KT5720 (3 microm), Rp-cAMPS (Rp-adenosine cyclic 3',5'-phosphorothioate) (100 microm), or PKI (100 microm). The above data suggest that L-type Ca2+ channels are functionally present in dendritic spines of CA1 pyramidal neurons, contribute to spine Ca2+ influx, and can be modulated by the beta2 adrenergic receptor through PKA in a highly compartmentalized manner.

Action Potentials↗