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The myogenic response sets the foundation for blood flow control. Recent findings suggest a role for G protein-coupled receptors (GPCR) and signaling pathways tied to the generation of reactive oxygen species (ROS). In this regard, this study ascertained the impact of NADPH oxidase (Nox) on myogenic tone in rat cerebral resistance arteries.The study employed real-time qPCR (RT-qPCR), pressure myography, and immunohistochemistry.GOur data highlight that vascular pressurization augments Nox1 activity and ensuing ROS production facilitates myogenic tone by limiting Ca

Objective— This study examined whether caveolae position Ca V 3.2 (T-type Ca2+ channel encoded by the α-3.2 subunit) sufficiently close to RyR (ryanodine receptors) for extracellular Ca 2+ influx to trigger Ca 2+ sparks and large-conductance Ca 2+ -activated K + channel feedback. Approach and Results— Using smooth muscle cells from mouse mesenteric arteries, the proximity ligation assay confirmed that Ca V 3.2 reside within 40 nm of caveolin 1, a key caveolae protein. Methyl-β-cyclodextrin, a cholesterol depleting agent that disrupts caveolae, suppressed Ca V 3.2 activity along with large-conductance Ca 2+ -activated K + –mediated spontaneous transient outward currents in cells from C57BL/6 but not Ca V 3.2 −/− mice. Genetic deletion of caveolin 1, a perturbation that prevents caveolae formation, also impaired spontaneous transient outward current production but did so without impairing Ca 2+ channel activity, including Ca V 3.2. These observations indicate a mistargeting of Ca V 3.2 in caveolin 1 −/− mice, a view supported by a loss of Ni 2+ -sensitive Ca 2+ spark generation and colocalization signal (Ca V 3.2-RyR) from the proximity ligation assay. Vasomotor and membrane potential measurements confirmed that cellular disruption of the Ca V 3.2-RyR axis functionally impaired the ability of large-conductance Ca 2+ -activated K + to set tone in pressurized caveolin 1 −/− arteries. Conclusions— Caveolae play a critical role in protein targeting and preserving the close structural relationship between Ca V 3.2 and RyR needed to drive negative feedback control in resistance arteries.

Key points In arterial smooth muscle, Ca2+ sparks are elementary Ca2+ -release events generated by ryanodine receptors (RyRs) to cause vasodilatation by opening maxi Ca2+ -sensitive K+ (BKCa ) channels. This study elucidated the contribution of T-type Cav 3.2 channels in caveolae and their functional interaction with L-type Cav 1.2 channels to trigger Ca2+ sparks in vascular smooth muscle cells (VSMCs). Our data demonstrate that L-type Cav 1.2 channels provide the predominant Ca2+ pathway for the generation of Ca2+ sparks in murine arterial VSMCs. T-type Cav 3.2 channels represent an additional source for generation of VSMC Ca2+ sparks. They are located in pit structures of caveolae to provide locally restricted, tight coupling between T-type Cav 3.2 channels and RyRs to ignite Ca2+ sparks. Abstract Recent data suggest that T-type Cav 3.2 channels in arterial vascular smooth muscle cells (VSMCs) and pits structure of caveolae could contribute to elementary Ca2+ signalling (Ca2+ sparks) via ryanodine receptors (RyRs) to cause vasodilatation. While plausible, their precise involvement in igniting Ca2+ sparks remains largely unexplored. The goal of this study was to elucidate the contribution of caveolar Cav 3.2 channels and their functional interaction with Cav 1.2 channels to trigger Ca2+ sparks in VSMCs from mesenteric, tibial and cerebral arteries. We used tamoxifen-inducible smooth muscle-specific Cav 1.2-/- (SMAKO) mice and laser scanning confocal microscopy to assess Ca2+ spark generation in VSMCs. Ni2+ , Cd2+ and methyl-β-cyclodextrin were used to inhibit Cav 3.2 channels, Cav 1.2 channels and caveolae, respectively. Ni2+ (50 μmol L-1 ) and methyl-β-cyclodextrin (10 mmol L-1 ) decreased Ca2+ spark frequency by ∼20-30% in mesenteric VSMCs in a non-additive manner, but failed to inhibit Ca2+ sparks in tibial and cerebral artery VSMCs. Cd2+ (200 μmol L-1 ) suppressed Ca2+ sparks in mesenteric arteries by ∼70-80%. A similar suppression of Ca2+ sparks was seen in mesenteric artery VSMCs of SMAKO mice. The remaining Ca2+ sparks were fully abolished by Ni2+ or methyl-β-cyclodextrin. Our data demonstrate that Ca2+ influx through CaV 1.2 channels is the primary means of triggering Ca2+ sparks in murine arterial VSMCs. CaV 3.2 channels, localized to caveolae and tightly coupled to RyR, provide an additional Ca2+ source for Ca2+ spark generation in mesenteric, but not tibial and cerebral, arteries.

Vascular T-type Ca2+ channels (CaV3.1 and CaV3.2) play a key role in arterial tone development. This study investigated whether this conductance is a regulatory target of angiotensin II (Ang II), a vasoactive peptide that circulates and which is locally produced within the arterial wall. Patch clamp electrophysiology performed on rat cerebral arterial smooth muscle cells reveals that Ang II (100 nM) inhibited T-type currents through AT1 receptor activation. Blocking protein kinase C failed to eliminate channel suppression, a finding consistent with unique signaling proteins enabling this response. In this regard, inhibiting NADPH oxidase (Nox) with apocynin or ML171 (Nox1 selective) abolished channel suppression highlighting a role for reactive oxygen species (ROS). In the presence of Ni2+ (50 µM), Ang II failed to modulate the residual T-type current, an observation consistent with this peptide targeting CaV3.2. Selective channel suppression by Ang II impaired the ability of CaV3.2 to alter spontaneous transient outward currents or vessel diameter. Proximity ligation assay confirmed Nox1 colocalization with CaV3.2. In closing, Ang II targets CaV3.2 channels via a signaling pathway involving Nox1 and the generation of ROS. This unique regulatory mechanism alters BKCa mediated feedback giving rise to a “constrictive” phenotype often observed with cerebrovascular disease.

The conducted vasomotor response reflects electrical communication in the arterial wall and the distance signals spread is regulated by three factors including resident ion channels. This study defined the role of inward-rectifying K+channels (KIR) in governing electrical communication along hamster cerebral arteries. Focal KCl application induced a vasoconstriction that conducted robustly, indicative of electrical communication among cells. Inhibiting dominant K+conductances had no attenuating effect, the exception being Ba2+blockade of KIR. Electrophysiology and Q-PCR analysis of smooth muscle cells revealed a Ba2+-sensitive KIRcurrent comprised of KIR2.1/2.2 subunits. This current was surprisingly small and when incorporated into a model, failed to account for the observed changes in conduction. We theorized a second population of KIRchannels exist and consistent with this idea, a robust Ba2+-sensitive KIR2.1/2.2 current was observed in endothelial cells. When both KIRcurrents were incorporated into, and then inhibited in our model, conduction decay was substantive, aligning with experiments. Enhanced decay was ascribed to the rightward shift in membrane potential and the increased feedback arising from voltage-dependent-K+channels. In summary, this study shows that two KIRpopulations work collaboratively to govern electrical communication and the spread of vasomotor responses along cerebral arteries.

Objective- This study examined whether caveolae position Ca

Human cerebral arteries contain three Ca2+ channel subtypes with distinct physiological roles., The regulation of arterial tone is critical in the spatial and temporal control of cerebral blood flow. Voltage-gated Ca2+ (CaV) channels are key regulators of excitation–contraction coupling in arterial smooth muscle, and thereby of arterial tone. Although L- and T-type CaV channels have been identified in rodent smooth muscle, little is known about the expression and function of specific CaV subtypes in human arteries. Here, we determined which CaV subtypes are present in human cerebral arteries and defined their roles in determining arterial tone. Quantitative polymerase chain reaction and Western blot analysis, respectively, identified mRNA and protein for L- and T-type channels in smooth muscle of cerebral arteries harvested from patients undergoing resection surgery. Analogous to rodents, CaV1.2 (L-type) and CaV3.2 (T-type) α1 subunits were expressed in human cerebral arterial smooth muscle; intriguingly, the CaV3.1 (T-type) subtype present in rodents was replaced with a different T-type isoform, CaV3.3, in humans. Using established pharmacological and electrophysiological tools, we separated and characterized the unique profiles of Ca2+ channel subtypes. Pressurized vessel myography identified a key role for CaV1.2 and CaV3.3 channels in mediating cerebral arterial constriction, with the former and latter predominating at higher and lower intraluminal pressures, respectively. In contrast, CaV3.2 antagonized arterial tone through downstream regulation of the large-conductance Ca2+-activated K+ channel. Computational analysis indicated that each Ca2+ channel subtype will uniquely contribute to the dynamic regulation of cerebral blood flow. In conclusion, this study documents the expression of three distinct Ca2+ channel subtypes in human cerebral arteries and further shows how they act together to orchestrate arterial tone.

Ca2+ sparks are generated in a voltage dependent manner to initiate spontaneous transient outward currents (STOC), events that moderate arterial constriction. In this study, we defined the mechanisms by which membrane depolarization increases Ca2+ sparks and subsequent STOC production. Using perforated patch clamp electrophysiology and rat cerebral arterial myocytes, we monitored STOC in the presence and absence of agents that modulate Ca2+ entry. Beginning with CaV3.2 inhibition, Ni2+ was shown to decrease STOC frequency in cells held at hyperpolarized (−40 mV) but not depolarized (−20 mV) voltages. In contrast, nifedipine, a CaV1.2 inhibitor, markedly suppressed STOC frequency at −20 mV but not −40 mV. These findings aligned with the voltage-dependent profiles of L- and T-type Ca2+ channels. Furthermore, computational and experimental observations illustrated that Ca2+ spark production is intimately tied to the activity of both conductances. Intriguingly, this study observed residual STOC production at depolarized voltages that was independent of CaV1.2 and CaV3.2. This residual component was insensitive to TRPV4 channel modulation and was abolished by Na+/Ca2+ exchange blockade. In summary, our work highlights that the voltage-dependent triggering of Ca2+ sparks/STOCs is not tied to a single conductance but rather reflects an interplay among multiple Ca2+ permeable pores with distinct electrophysiological properties. This integrated orchestration enables smooth muscle to grade Ca2+ spark/STOC production and thus precisely tune negative electrical feedback. This article is protected by copyright. All rights reserved

Ca2+ sparks are generated in a voltage dependent manner to initiate spontaneous transient outward currents (STOC) that antagonize arterial constriction. In the present study, we defined the mechanisms by which membrane depolarization increases Ca2+ sparks and subsequent STOC production. Using perforated patch clamp electrophysiology and rat cerebral arterial myocytes, we monitored STOC in the presence and absence of agents that modulate Ca2+ entry pathways. Beginning with the CaV3.2 inhibitor Ni2+, STOC frequency decreased in cells held at hyperpolarized voltage (-40 mV). In contrast, CaV1.2 inhibition with nifedipine suppressed STOC frequency at depolarized potential (-20 mV). These findings are consistent with the voltage-dependent profiles of L- and T-type Ca2+ channels; and were replicated in a computational model of Ca2+ spark production. Upon concomitant CaV1.2 and CaV3.2 blockade, we further observed residual voltage-independent STOC production. This residual component was insensitive to stimulatio...

Objectives This study aims to further elucidate the role of adrenergic transmission in erection and to highlight whether adrenergic transmission in the penis modulates sildenafil's action. Methods measurement of intracavernosal pressure in the anesthetized rat model. Key findings Guanethidine (3 and 6 mg/kg) potentiated intracavernosal pressure/mean arterial pressure (ICP/MAP) rises in response to cavernous nerve stimulation by 4.375 ± 0.425 and 18.375 ± 1.085% respectively. Propranolol did the opposite. In presence of guanethidine, sildenafil (0.01, 0.1 and 1 mg/kg) potentiated ICP/MAP responses by 81.571 ± 4.918%, 147.83 ± 10.864% and 279.285 ± 23.053% at 1 Hz compared to 22.277 ± 2.139%, 123.571 ± 8.443% and 186.25 ± 13.542% respectively in the absence of guanethidine. Propranolol inhibited the effect sildenafil at all frequencies of stimulation. Verapamil exhibited a pro-erectile action and potentiated the effect of sildenafil (0.01, 0.1 and 1 mg/kg) on erectile responses corresponding to 85.25 ± 6.716%, 146 ± 11.288% and 221.571 ± 19.032% respectively compared to 26.011 ± 1.911%, 87.142 ± 8.73% and 182.2 ± 16.921% in its absence. Conclusions This study provides functional evidence that inhibition of sympathetic tone peripherally results in enhancement of erectile function. β-adrenergic receptors seem to play an important role in erection. The combination of sildenafil and guanethidine or verapamil could have a potential advantage on erectile function but propranolol may mask the effect of sildenafil on erectile function.