scholarly journals Orientation of palmitoylated CaVβ2a relative to CaV2.2 is critical for slow pathway modulation of N-type Ca2+ current by tachykinin receptor activation

2009 ◽  
Vol 134 (5) ◽  
pp. 385-396 ◽  
Author(s):  
Tora Mitra-Ganguli ◽  
Iuliia Vitko ◽  
Edward Perez-Reyes ◽  
Ann R. Rittenhouse
Keyword(s):  
Amino Acids ◽  
Arachidonic Acid ◽  
Palmitic Acid ◽  
Receptor Activation ◽  
Slow Pathway ◽  
Channel Activity ◽  
Tachykinin Receptor ◽  
Previous Hypothesis ◽  
Inhibitory Site ◽  
Neurokinin 1

The Gq-coupled tachykinin receptor (neurokinin-1 receptor [NK-1R]) modulates N-type Ca2+ channel (CaV2.2 or N channel) activity at two distinct sites by a pathway involving a lipid metabolite, most likely arachidonic acid (AA). In another study published in this issue (Heneghan et al. 2009. J. Gen Physiol. doi:10.1085/jgp.200910203), we found that the form of modulation observed depends on which CaVβ is coexpressed with CaV2.2. When palmitoylated CaVβ2a is coexpressed, activation of NK-1Rs by substance P (SP) enhances N current. In contrast, when CaVβ3 is coexpressed, SP inhibits N current. However, exogenously applied palmitic acid minimizes this inhibition. These findings suggested that the palmitoyl groups of CaVβ2a may occupy an inhibitory site on CaV2.2 or prevent AA from interacting with that site, thereby minimizing inhibition. If so, changing the orientation of CaVβ2a relative to CaV2.2 may displace the palmitoyl groups and prevent them from antagonizing AA's actions, thereby allowing inhibition even in the presence of CaVβ2a. In this study, we tested this hypothesis by deleting one (Bdel1) or two (Bdel2) amino acids proximal to the α interacting domain (AID) of CaV2.2's I–II linker. CaVβs bind tightly to the AID, whereas the rigid region proximal to the AID is thought to couple CaVβ's movements to CaV2.2 gating. Although Bdel1/β2a currents exhibited more variable enhancement by SP, Bdel2/β2a current enhancement was lost at all voltages. Instead, inhibition was observed that matched the profile of N-current inhibition from CaV2.2 coexpressed with CaVβ3. Moreover, adding back exogenous palmitic acid minimized inhibition of Bdel2/β2a currents, suggesting that when palmitoylated CaVβ2a is sufficiently displaced, endogenously released AA can bind to the inhibitory site. These findings support our previous hypothesis that CaVβ2a's palmitoyl groups directly interact with an inhibitory site on CaV2.2 to block N-current inhibition by SP.

Increased tachykinin receptor gene expression in asthmatic lung and its modulation by steroids

1993 ◽  
Vol 11 (1) ◽  
pp. 1-7 ◽  
Author(s):  
I M Adcock ◽  
M Peters ◽  
C Gelder ◽  
H Shirasaki ◽  
C R Brown ◽  
...  
Keyword(s):  
Gene Expression ◽  
Chronic Inflammation ◽  
Northern Blot Analysis ◽  
Receptor Gene ◽  
Sensory Nerves ◽  
R Gene ◽  
Dexamethasone Treatment ◽  
Tachykinin Receptor ◽  
Neurokinin 1 ◽  
Receptor Gene Expression

ABSTRACT Substance P has several inflammatory effects on the airways mediated via neurokinin 1 receptors (NK1Rs) and, if released from sensory nerves, may amplify the chronic inflammation seen in asthma. Northern blot analysis of NK1R mRNA in lung showed a 52 ± 10% (s.e.m.; P<0·01) increase in mRNA in the asthmatic lung compared with non-asthmatic control tissue. NK1R mRNA was reduced by 84·5 ± 1·9% after incubation with dexamethasone (1 μm) for 3 h (P<0·01). In contrast, NK2R mRNA was unaltered in asthmatic lungs and dexamethasone treatment had no effect on the level of NK2R mRNA. These results suggest that chronic inflammation in asthma may result in increased NK1R gene expression and that this effect is reversed by glucocorticosteroids.

Action of substance P (neurokinin-1) receptor activation on rat neostriatal projection neurons

Synapse ◽  
1999 ◽  
Vol 33 (1) ◽  
pp. 26-35 ◽  
Author(s):  
Elvira Galarraga ◽  
Salvador Hern�ndez-L�pez ◽  
Dagoberto Tapia ◽  
Arturo Reyes ◽  
Jos� Bargas
Keyword(s):  
Substance P ◽  
Receptor Activation ◽  
Projection Neurons ◽  
Neurokinin 1 Receptor ◽  
Neurokinin 1

Intravenously injected [1-14C]arachidonic acid targets phospholipids, and [1-14C]palmitic acid targets neutral lipids in hearts of awake rats

Lipids ◽  
2000 ◽  
Vol 35 (8) ◽  
pp. 891-898 ◽  
Author(s):  
Eric J. Murphy ◽  
Thad A. Rosenberger ◽  
Casey B. Patrick ◽  
Stanley I. Rapoport
Keyword(s):  
Arachidonic Acid ◽  
Palmitic Acid ◽  
Neutral Lipids ◽  
Awake Rats

Arachidonic acid inhibits K channels in basolateral membrane of the thick ascending limb

2002 ◽  
Vol 283 (3) ◽  
pp. F407-F414 ◽  
Author(s):  
Rui-Min Gu ◽  
Wen-Hui Wang
Keyword(s):  
Arachidonic Acid ◽  
Basolateral Membrane ◽  
Inhibitory Effect ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
K Channels ◽  
Cytochrome P 450

We have used the patch-clamp technique to study the effect of arachidonic acid (AA) on the basolateral K channels in the medullary thick ascending limb (mTAL) of rat kidney. An inwardly rectifying 50-pS K channel was identified in cell-attached and inside-out patches in the basolateral membrane of the mTAL. The channel open probability ( P o) was 0.51 at the spontaneous cell membrane potential and decreased to 0.25 by 30 mV hyperpolarization. The addition of 5 μM AA decreased channel activity, identified as NP o, from 0.58 to 0.08 in cell-attached patches. The effect of AA on the 50-pS K channel was specific because 10 μM cis-11,14,17-eicosatrienoic acid had no significant effect on channel activity. To determine whether the effect of AA was mediated by AA per se or by its metabolites, we examined the effect of AA on channel activity in the presence of indomethacin, an inhibitor of cyclooxygenase, or N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), an inhibitor of cytochrome P-450 monooxygenase. Inhibition of cyclooxygenase increased channel activity from 0.54 to 0.9. However, indomethacin did not abolish the inhibitory effect of AA on the 50-pS K channel. In contrast, inhibition of cytochrome P-450 metabolism not only increased channel activity from 0.49 to 0.83 but also completely abolished the effect of AA. Moreover, addition of DDMS can reverse the inhibitory effect of AA on channel activity. The notion that the effect of AA was mediated by cytochrome P-450-dependent metabolites of AA is also supported by the observation that addition of 100 nM of 20-hydroxyeicosatetraenoic acid, a main metabolite of AA in the mTAL, can mimic the effect of AA. We conclude that AA inhibits the 50-pS K channel in the basolateral membrane of the mTAL and that the effect of AA is mainly mediated by cytochrome P-450-dependent metabolites of AA.

Arachidonic acid enhances contraction and intracellular Ca2+ transients in individual rat ventricular myocytes

1997 ◽  
Vol 272 (1) ◽  
pp. H350-H359 ◽  
Author(s):  
D. S. Damron ◽  
B. A. Summers
Keyword(s):  
Arachidonic Acid ◽  
Protein Kinase C ◽  
Protein Kinase ◽  
Cardiac Muscle ◽  
Ventricular Myocytes ◽  
Contractile Function ◽  
Receptor Activation ◽  
K Channels ◽  
Rat Ventricular Myocytes ◽  
Kinase C

Modulation of intracellular free Ca2+ concentration ([Ca2+]i) by inotropic stimuli alters contractility in cardiac muscle. Arachidonic acid (AA), a precursor for eicosanoid formation, is released in response to receptor activation and myocardial ischemia and has been demonstrated to alter K+ and Ca2+ channel activity. We investigated the effects of AA on contractility by simultaneously measuring [Ca2+]i and shortening in single field-stimulated rat ventricular myocytes. [Ca2+]i transients were measured using fura 2, and myocyte shortening was assessed using video edge detection. AA stimulated a doubling in the amplitude of the [Ca2+]i transient and a twofold increase in myocyte shortening. In addition, AA stimulated a 30% increase in the time to 50% diastolic [Ca2+]i and a 35% increase in the time to 50% relengthening. These effects of AA were mediated by AA itself (56 +/- 5%) and by cyclooxygenase metabolites. Pretreatment with the protein kinase C inhibitors staurosporine and chelerythrine nearly abolished (> 90% inhibition) these AA-induced effects. Inhibition of voltagegated K+ channels with 4-aminopyridine mimicked the effects of AA. Addition of AA to the 4-aminopyridine-treated myocyte had no additional effect on parameters of contractile function. These data indicate that AA alters the amplitude and duration of Ca2- transients and myocyte shortening via protein kinase C-dependent inhibition of voltage-gated K+ channels. Release of AA by phospholipases in response to receptor activation by endogenous mediators or pathological stimuli may be involved in mediating inotropic responses in cardiac muscle.

ATP-sensitive K channel modulation by products of PLA2 action in the insulin-secreting HIT cell line

1995 ◽  
Vol 268 (1) ◽  
pp. C181-C190 ◽  
Author(s):  
G. T. Eddlestone
Keyword(s):  
Arachidonic Acid ◽  
Cell Line ◽  
Katp Channel ◽  
Tumor Cell Line ◽  
Cyclooxygenase Inhibitors ◽  
K Channel ◽  
Channel Activity ◽  
Membrane Phospholipids ◽  
Venom Component ◽  
Inside Out

Insulin secretion from the islets of Langerhans may be initiated or potentiated by increased phospholipase A2 (PLA2) activity. This patch-clamp study of the insulin-secreting HIT tumor cell line assessed whether inhibition of the ATP-sensitive potassium (KATP) channel, which modulates the secretion-associated beta-cell electrical activity, contributes to the secretory response to PLA2. Exogenous PLA2 (100-1,000 mU/ml) reversibly suppressed KATP channel activity in excised inside-out patches. Similarly, mellitin (0.5-5 micrograms/ml), a bee venom component that increases phospholipid susceptibility to metabolism by PLA2, suppressed KATP channel activity, suggesting that PLA2 is present in excised patches. Adding low concentrations of particular lysophospholipids or arachidonic acid also reduced KATP channel activity in excised inside-out patches. In cell-attached patches, the lysophospholipids had a similar effect, whereas arachidonic acid caused channel stimulation; this latter effect was reversed by cyclooxygenase inhibitors. A recently identified ATP-stimulated PLA2 in beta-cells has been proposed as an important mediator of stimulus-secretion coupling in response to nutrients. The present data illustrating that initial products of PLA2 action on membrane phospholipids reduce KATP channel activity indicate a mechanism that may contribute an early stimulatory signal in this pathway. The observation that metabolism of arachidonate via the cyclooxygenase pathway causes KATP channel stimulation demonstrates a potential counterregulatory mechanism.

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