A spoonful of sugar helps the KV channel activity go down.
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Animals↗
Biomedical subjects
Stephen V Straub
Publications and source records attributed to Stephen V Straub.
Molecular coding of Kv1 channels to oppose myogenic constriction.
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Animals↗
Local potassium signaling couples neuronal activity to vasodilation in the brain.
The mechanisms by which active neurons, via astrocytes, rapidly signal intracerebral arterioles to dilate remain obscure. Here we show that modest elevation of extracellular potassium (K+) activated inward rectifier K+ (Kir) channels and caused membrane potential hyperpolarization in smooth muscle cells (SMCs) of intracerebral arterioles and, in cortical brain slices, induced Kir-dependent vasodilation and suppression of SMC intracellular calcium (Ca2+) oscillations. Neuronal activation induced a rapid (<2 s latency) vasodilation that was greatly reduced by Kir channel blockade and completely abrogated by concurrent cyclooxygenase inhibition. Astrocytic endfeet exhibited large-conductance, Ca2+-sensitive K+ (BK) channel currents that could be activated by neuronal stimulation. Blocking BK channels or ablating the gene encoding these channels prevented neuronally induced vasodilation and suppression of arteriolar SMC Ca2+, without affecting the astrocytic Ca2+ elevation. These results support the concept of intercellular K+ channel-to-K+ channel signaling, through which neuronal activity in the form of an astrocytic Ca2+ signal is decoded by astrocytic BK channels, which locally release K+ into the perivascular space to activate SMC Kir channels and cause vasodilation.
Animals↗
Dynamic inositol trisphosphate-mediated calcium signals within astrocytic endfeet underlie vasodilation of cerebral arterioles.
Active neurons communicate to intracerebral arterioles in part through an elevation of cytosolic Ca(2+) concentration ([Ca(2+)](i)) in astrocytes, leading to the generation of vasoactive signals involved in neurovascular coupling. In particular, [Ca(2+)](i) increases in astrocytic processes ("endfeet"), which encase cerebral arterioles, have been shown to result in vasodilation of arterioles in vivo. However, the spatial and temporal properties of endfoot [Ca(2+)](i) signals have not been characterized, and information regarding the mechanism by which these signals arise is lacking. [Ca(2+)](i) signaling in astrocytic endfeet was measured with high spatiotemporal resolution in cortical brain slices, using a fluorescent Ca(2+) indicator and confocal microscopy. Increases in endfoot [Ca(2+)](i) preceded vasodilation of arterioles within cortical slices, as detected by simultaneous measurement of endfoot [Ca(2+)](i) and vascular diameter. Neuronal activity-evoked elevation of endfoot [Ca(2+)](i) was reduced by inhibition of inositol 1,4,5-trisphosphate (InsP(3)) receptor Ca(2+) release channels and almost completely abolished by inhibition of endoplasmic reticulum Ca(2+) uptake. To probe the Ca(2+) release mechanisms present within endfeet, spatially restricted flash photolysis of caged InsP(3) was utilized to liberate InsP(3) directly within endfeet. This maneuver generated large amplitude [Ca(2+)](i) increases within endfeet that were spatially restricted to this region of the astrocyte. These InsP(3)-induced [Ca(2+)](i) increases were sensitive to depletion of the intracellular Ca(2+) store, but not to ryanodine, suggesting that Ca(2+)-induced Ca(2+) release from ryanodine receptors does not contribute to the generation of endfoot [Ca(2+)](i) signals. Neuronally evoked increases in astrocytic [Ca(2+)](i) propagated through perivascular astrocytic processes and endfeet as multiple, distinct [Ca(2+)](i) waves and exhibited a high degree of spatial heterogeneity. Regenerative Ca(2+) release processes within the endfeet were evident, as were localized regions of Ca(2+) release, and treatment of slices with the vasoactive neuropeptides somatostatin and vasoactive intestinal peptide was capable of inducing endfoot [Ca(2+)](i) increases, suggesting the potential for signaling between local interneurons and astrocytic endfeet in the cortex. Furthermore, photorelease of InsP(3) within individual endfeet resulted in a local vasodilation of adjacent arterioles, supporting the concept that astrocytic endfeet function as local "vasoregulatory units" by translating information from active neurons into complex InsP(3)-mediated Ca(2+) release signals that modulate arteriolar diameter.
Animals↗
cAMP potentiates ATP-evoked calcium signaling in human parotid acinar cells.
In salivary acinar cells, intracellular calcium ([Ca(2+)](i)) signaling plays an important role in eliciting fluid secretion through the activation of Ca(2+)-activated ionic conductances. Ca(2+) and cAMP have synergistic effects on fluid secretion such that peak secretion is elicited following activation of both parasympathetic and sympathetic pathways. We have recently demonstrated that cAMP exerts effects on Ca(2+) release, through protein kinase A (PKA)-mediated phosphorylation of inositol 1,4,5-trisphosphate receptors (InsP(3)R) in mouse parotid acinar cells. To extend these findings, in the present study cross-talk between Ca(2+) signaling and cAMP pathways in human parotid acinar cells was investigated. In human parotid acinar cells, carbachol stimulation evoked increases in the [Ca(2+)](i) and the initial peak amplitude was enhanced following PKA activation, consistent with reports from mouse parotid. Stimulation with ATP also evoked an increase in [Ca(2+)](i). The ATP-evoked Ca(2+) elevation was largely dependent on extracellular Ca(2+), suggesting the involvement of the P2X family of purinergic receptors. Pharmacological elevation of cAMP resulted in a approximately 5-fold increase in the peak [Ca(2+)](i) change evoked by ATP stimulation. This enhanced [Ca(2+)](i) increase was not dependent on intracellular release from InsP(3)R or ryanodine receptors, suggesting a direct effect on P2XR. Reverse transcription-polymerase chain reaction and Western blot analysis confirmed the presence of P2X(4)R and P2X(7)R mRNA and protein in human parotid acinar cells. ATP-activated cation currents were studied using whole cell patch clamp techniques in HEK-293 cells, a null background for P2XR. Raising cAMP resulted in a approximately 4.5-fold enhancement of ATP-activated current in HEK-293 cells transfected with P2X(4)R DNA but had no effects on currents in cells expressing P2X(7)R. These data indicate that in human parotid acinar cells, in addition to modulation of Ca(2+) release, Ca(2+) influx through P2X(4)R may constitute a further locus for the synergistic effects of Ca(2+) and PKA activation.
Adenosine Triphosphate↗
Modulation of cytosolic calcium signaling by protein kinase A-mediated phosphorylation of inositol 1,4,5-trisphosphate receptors.
Calcium release via intracellular Ca2+ release channels is a central event underpinning the generation of numerous, often divergent physiological processes. In electrically non-excitable cells, this Ca2+ release is brought about primarily through activation of inositol 1,4,5-trisphosphate receptors and typically takes the form of calcium oscillations. It is widely believed that information is carried in the temporal and spatial characteristics of these signals. Furthermore, stimulation of individual cells with different agonists can generate Ca2+ oscillations with dramatically different spatial and temporal characteristics. Thus, mechanisms must exist for the acute regulation of Ca2+ release such that agonist-specific Ca2+ signals can be generated. One such mechanism by which Ca2+ signals can be modulated is through simultaneous activation of multiple second messenger pathways. For example, activation of both the InsP3 and cAMP pathways leads to the modulation of Ca2+ release through protein kinase A mediated phosphoregulation of the InsP3R. Indeed, each InsP3R subtype is a potential substrate for PKA, although the functional consequences of this phosphorylation are not clear. This review will focus on recent advances in our understanding of phosphoregulation of InsP3R, as well as the functional consequences of this modulation in terms of eliciting specific cellular events.
Animals↗
Crosstalk between cAMP and Ca2+ signaling in non-excitable cells.
An impressive array of cytosolic calcium ([Ca2+](i)) signals exert control over a broad range of physiological processes. The specificity and fidelity of these [Ca2+](i) signals is encoded by the frequency, amplitude, and sub-cellular localization of the response. It is believed that the distinct characteristics of [Ca2+](i) signals underlies the differential activation of effectors and ultimately cellular events. This "shaping" of [Ca2+](i) signals can be achieved by the influence of additional signaling pathways modulating the molecular machinery responsible for generating [Ca2+](i) signals. There is a particularly rich source of potential sites of crosstalk between the cAMP and the [Ca2+](i) signaling pathways. This review will focus on the predominant molecular loci at which these classical signaling systems interact to impact the spatio-temporal pattern of [Ca2+](i) signaling in non-excitable cells.
Animals↗
A role for phosphorylation of inositol 1,4,5-trisphosphate receptors in defining calcium signals induced by Peptide agonists in pancreatic acinar cells.
Stimulation of pancreatic acinar cells with acetylcholine (ACh) and cholecystokinin (CCK) results in an elevation of cytosolic calcium ([Ca(2+)](c)) through activation of inositol 1,4,5-trisphosphate receptors (InsP(3)R). The global temporal pattern of the [Ca(2+)](c) changes produced by ACh or CCK stimulation differs significantly. The hypothesis was tested that CCK stimulation results in a protein kinase A (PKA)-mediated phosphorylation of InsP(3)R and this event contributes to the generation of agonist-specific [Ca(2+)](c) signals. Physiological concentrations of CCK evoked phosphorylation of the type III InsP(3)R, which was blocked by pharmacological inhibition of PKA. Imaging of fura-2-loaded acinar cells revealed that the rate of [Ca(2+)](c) rise during CCK-evoked oscillations slows with each subsequent oscillation, consistent with a developing modulation of release, whereas the kinetics of ACh-evoked oscillations remain constant. Stimulation of cells with ACh following activation of PKA resulted in a slowing of the ACh-evoked [Ca(2+)](c) rise, which now resembled a time-matched CCK response. PKA activation also resulted in a slowing of [Ca(2+)](c) increases elicited by photolysis of caged InsP(3). Targeted, PKA-mediated phosphorylation of type III InsP(3)R is involved in a physiological CCK response, as disruption of the targeting of PKA with the peptide HT31 resulted in marked changes in the CCK-evoked [Ca(2+)](c) signal but had no effect on ACh-evoked responses. Stimulation of cells with bombesin, which evokes [Ca(2+)](c) oscillations indistinguishable from those produced by CCK, also results in PKA-mediated phosphorylation of type III InsP(3)R. Thus, we conclude that PKA-mediated phosphorylation of type III InsP(3)R is a general mechanism by which the patterns of [Ca(2+)](c) oscillations are shaped in pancreatic acinar cells.
Acetylcholine↗
Cytosolic Ca(2+) and Ca(2+)-activated Cl(-) current dynamics: insights from two functionally distinct mouse exocrine cells.
The dynamics of Ca(2+) release and Ca(2+)-activated Cl(-) currents in two related, but functionally distinct exocrine cells, were studied to gain insight into how the molecular specialization of Ca(2+) signalling machinery are utilized to produce different physiological endpoints: in this case, fluid or exocytotic secretion. Digital imaging and patch-clamp methods were used to monitor the temporal and spatial properties of changes in cytosolic Ca(2+) concentration ([Ca(2+)](c)) and Cl(-) currents following the controlled photolytic release of caged-InsP(3) or caged-Ca(2+). In parotid and pancreatic acinar cells, changes in [Ca(2+)](c) and activation of a Ca(2+)-activated Cl(-) current occurred with close temporal coincidence. In parotid, a rapid global Ca(2+) signal was invariably induced, even with low-level photolytic release of threshold amounts of InsP(3). In pancreas, threshold stimulation generated an apically delimited [Ca(2+)](c) signal, while a stronger stimulus induced a global [Ca(2+)](c) signal which exhibited characteristics of a propagating wave. InsP(3) was more effective in parotid, where [Ca(2+)](c) signals initiated with shorter latency and exhibited a faster time-to-peak than in pancreas. The increased potency of InsP(3) in parotid probably results from a four-fold higher number of InsP(3) receptors as measured by radiolabelled InsP(3) binding and western blot analysis. The Ca(2+) sensitivity of the Cl(-) channels in parotid and pancreas was determined from the [Ca(2+)]-current relationship measured during a dynamic 'Ca(2+) ramp' produced by the continuous, low-level photolysis of caged-Ca(2+). In addition to a greater number of InsP(3) receptors, the Cl(-) current density of parotid acinar cells was more than four-fold greater than that of pancreatic cells. Whereas activation of the current was tightly coupled to increases in Ca(2+) in both cell types, local Ca(2+) clearance was found to contribute substantially to the deactivation of the current in parotid. These data reveal specializations of common modules of Ca(2+)-release machinery and subsequent effector activation that are specifically suited to the distinct functional roles of these two related cell types.
Algorithms↗