Sarcoplasmic reticulum in vascular cells in hypertension and during proliferation

Sarcoplasmic reticulum calcium ATPase (SERCA) proteolysis by matrix metalloproteinase-2 contributes to vascular dysfunction in early hypertension

AIMS

Hypertension is associated with an increased activity of matrix metalloproteinase (MMP)-2 in the vasculature, which, in turn, proteolyzes extra- and intracellular proteins that lead to vascular dysfunction. The activity of sarcoplasmic reticulum calcium ATPase (SERCA) is decreased in the aortas of hypertensive rats. Increased activity of MMP-2 proteolyzed SERCA in rat heart during ischemia and reperfusion injury, thus impairing cardiac function. Therefore, we examined whether increased activity of MMP-2 in early hypertension contributes to proteolyze SERCA in the aortas, thus leading to maladaptive vascular remodeling and dysfunction.

MAIN METHODS

Male Sprague-Dawley rats were submitted to two kidney-one clip (2K-1C) or Sham surgery and treated with doxycycline. Systolic blood pressure (SBP) was assessed by tail-cuff plethysmography. After 7 days, aortas were collected for zymography assays, Western blot to SERCA, ATPase activity assay, vascular reactivity, Ki-67 immunofluorescence and hematoxylin/eosin stain.

KEY FINDINGS

SBP was increased in 2K-1C rats and doxycycline did not reduce it, but decreased MMP-2 activity and prevented SERCA proteolysis in aortas. Cross sectional area, media to lumen ratio and Ki-67 were all increased in the aortas of hypertensive rats and doxycycline decreased Ki-67. In 2K-1C rats, arterial relaxation to acetylcholine was impaired and doxycycline ameliorated it.

SIGNIFICANCE

doxycycline reduced MMP-2 activity in aortas of 2K-1C rats and prevented proteolysis of SERCA and its dysfunction, thus ameliorating hypertension-induced vascular dysfunction.

Effects of plant extracts and derivatives on cardiac K+, Nav, and Cav channels: a review

Natural products (NPs) are endless sources of compounds for fighting against several pathologies. Many dysfunctions, including cardiovascular disorders, such as cardiac arrhythmias have their modes of action regulation of the concentration of electrolytes inside and outside the cell targeting ion channels. Here, we highlight plant extracts and secondary metabolites' effects on the treatment of related cardiac pathologies on hERG, Nav, and Cav of cardiomyocytes. The natural product's pharmacology of expressed receptors like alpha-adrenergic receptors causes an influx of Ca2+ ions through receptor-operated Ca2+ ion channels. We also examine the NPs associated with cardiac contractions such as myocardial contractility by reducing the L-type calcium current and decreasing the intracellular calcium transient, inhibiting the K+ induced contractions, decreasing amplitude of myocyte shortening and showed negative ionotropic and chronotropic effects due to decreasing cytosolic Ca2+. We examine whether the NPs block potassium channels, particular the hERG channel and regulatory effects on Nav1.7.

Investigation of the mechanisms of Angelica dahurica root extract-induced vasorelaxation in isolated rat aortic rings

BACKGROUND

The root of Angelica dahurica Bentham et Hooker (Umbelliferae) has been used as a traditional medicine for colds, headache, dizziness, toothache, supraorbital pain, nasal congestion, acne, ulcer, carbuncle, and rheumatism in China, Japan, and Korea. Interestingly, it has been used in the treatment of vascular diseases including hypertension. The aim of this study was to provide pharmacological evidence for the anti-hypertensive effect of A. dahurica by investigating the mechanism underlying its vasorelaxant effect.

METHODS

The vasorelaxant effects of a 70% methanol extract of the A. dahurica root (ADE) on rat thoracic aorta and its underlying mechanisms were assessed. Isolated rat aortic rings were suspended in organ chambers containing 10 ml Krebs-Henseleit (K-H) solution and placed between 2 tungsten stirrups and connected to an isometric force transducer. Changes in tension were recorded via isometric transducers connected to a data acquisition system.

RESULTS

ADE causes concentration-dependent relaxation in both endothelium-intact and endothelium-denuded aortic rings precontracted with phenylephrine (PE; 1 μM) or potassium (KCl; 60 mM) in K-H solution. And pre-treatment with ADE (1 mg/ml) inhibited calcium-induced vasocontraction of aortic rings induced by PE or KCl. However, ADE pre-treatment did not affect the contraction induced by PE or caffeine in Ca(2+)-free K-H solution.

CONCLUSIONS

These results suggested that the ADE has vasorelaxant effect and the vasorelaxant activity is mediated by endothelium-independent pathway that includes the blockade of extracellular calcium influx through the receptor-operated Ca(2+) channel and voltage-dependent calcium channel pathways.

Gene Expression in Experimental Aortic Coarctation and Repair: Candidate Genes for Therapeutic Intervention?

Coarctation of the aorta (CoA) is a constriction of the proximal descending thoracic aorta and is one of the most common congenital cardiovascular defects. Treatments for CoA improve life expectancy, but morbidity persists, particularly due to the development of chronic hypertension (HTN). Identifying the mechanisms of morbidity is difficult in humans due to confounding variables such as age at repair, follow-up duration, coarctation severity and concurrent anomalies. We previously developed an experimental model that replicates aortic pathology in humans with CoA without these confounding variables, and mimics correction at various times using dissolvable suture. Here we present the most comprehensive description of differentially expressed genes (DEGs) to date from the pathology of CoA, which were obtained using this model. Aortic samples (n=4/group) from the ascending aorta that experiences elevated blood pressure (BP) from induction of CoA, and restoration of normal BP after its correction, were analyzed by gene expression microarray, and enriched genes were converted to human orthologues. 51 DEGs with >6 fold-change (FC) were used to determine enriched Gene Ontology terms, altered pathways, and association with National Library of Medicine Medical Subject Headers (MeSH) IDs for HTN, cardiovascular disease (CVD) and CoA. The results generated 18 pathways, 4 of which (cell cycle, immune system, hemostasis and metabolism) were shared with MeSH ID’s for HTN and CVD, and individual genes were associated with the CoA MeSH ID. A thorough literature search further uncovered association with contractile, cytoskeletal and regulatory proteins related to excitation-contraction coupling and metabolism that may explain the structural and functional changes observed in our experimental model, and ultimately help to unravel the mechanisms responsible for persistent morbidity after treatment for CoA.

Vasorelaxant effect of osterici radix ethanol extract on rat aortic rings

The root of Ostericum koreanum Maximowicz has been used as a traditional medicine called “Kanghwal” in Korea (or “Qianghuo” in China). The purpose of this study was to investigate the vasorelaxant activity and mechanism of action of an ethanol extract of the O. koreanum root (EOK). We used isolated rat aortic rings to assess the effects of EOK on various vasorelaxant or vasoconstriction factors. EOK induced vasorelaxation in phenylephrine hydrochloride (PE) or KCl precontracted aortic rings in a concentration-dependent manner. However, the vasorelaxant effects of EOK on endothelium-intact aortic rings were reduced by pretreatment with L-NAME or methylene blue. In Ca²⁺-free Krebs-Henseleit solution, pretreatment with EOK (0.3 mg/mL) completely inhibited PE-induced constriction. In addition, EOK (0.3 mg/mL) also completely inhibited vasoconstriction induced by supplemental Ca²⁺ in aortic rings that were precontracted with PE or KCl. Furthermore, the EOK-induced vasorelaxation in PE-contracted aortic rings was inhibited by preincubation with nifedipine. These results indicate that the vasorelaxant effects of EOK are responsible for the induction of NO formation from L-Arg and NO-cGMP pathways, blockage of the extracellular Ca²⁺ entry via the receptor-operative Ca²⁺ channel and voltage-dependent calcium channel, and blockage of sarcoplasmic reticulum Ca²⁺ release via the inositol triphosphate pathway.

Aqueous fraction from Costus spiralis (Jacq.) Roscoe leaf reduces contractility by impairing the calcium inward current in the mammalian myocardium

ETHNOPHARMACOLOGICAL RELEVANCE

Brazilian folk medicine uses infusion of Costus spiralis leaf to help people to treat arterial hypertension and syndromes of cardiac hyperexcitability.

AIM OF THE STUDY

Evaluate the aqueous fraction (AqF) effect on atrial contractility and investigate its mechanism of action.

MATERIALS AND METHODS

The AqF effect on the cardiac contractility was studied on isolated electrically driven guinea pig left atria. Atropine and tetraethylammonium (TEA) were employed to investigate whether potassium contributes for the inotropic mechanism of the AqF. The role of calcium in this effect was also studied. This was done by analysing the AqF effect on the Bowditch's phenomenon, as well as by studying whether it could interfere with the concentration-effect curve for CaCl(2), isoproterenol, and BAY K8644. Mice isolated cardiomyocytes were submitted to a whole-cell patch-clamp technique in order to evaluate whether the L-type calcium current participates on the AqF effect. Furthermore, the intracellular calcium transient was studied by confocal fluorescence microscopy.

RESULTS

AqF depressed the atrial contractile force. It was the most potent fraction from C. spiralis leaf (EC(50)=305 ± 41 mg/l) (crude extract: EC(50)=712 ± 41; ethyl acetate: EC(50)=788 ± 121; chloroform: EC(50)=8,948 ± 1,346 mg/l). Sodium and potassium content in the AqF was 0.15 mM and 1.91 mM, respectively. Phytochemical analysis revealed phenols, tannins, flavones, xanthones, flavonoids, flavonols, flavononols, flavonones, and saponins. Experiments with atropine and TEA showed that potassium does not participate of the inotropic mechanism of AqF. However, this fraction decreased the force overshoot characteristic of the Bowditch's phenomenon, and shifted the concentration-response curve for CaCl(2) (EC(50) from 1.12 ± 0.07 to 7.23 ± 0.47 mM) indicating that calcium currents participate on its mechanism of action. Results obtained with isoproterenol (1-1,000 pM) and BAY K8644 (5-2000nM) showed that AqF abolished the inotropic effect of these substances. On cardiomyocytes, 48mg/l AqF reduced (∼23%) the L-type calcium current density from -6.3 ± 0.3 to -4.9 ± 0.2 A/F (n=5 cells, p<0.05) and reduced the intracellular calcium transient (∼20%, 4.7 ± 1.2 a.u., n=42 cells to 3.7 ± 1.00 a.u., n=35 cells, p<0.05). However, the decay time of the fluorescence was not changed (control: 860 ± 32 ms, n=42 cells; AqF: 876 ± 26 ms, n=35 cells, p>0.05).

CONCLUSIONS

The AqF of C. spiralis leaf depresses myocardial contractility by reducing the L-type calcium current and by decreasing the intracellular calcium transient. Despite the lack of data on the therapeutic dose of AqF used in folk medicine, our results support, at least in part, the traditional use of this plant to treat cardiac disorders.

Intracellular Ca2+ storage in health and disease: a dynamic equilibrium

Homeostatic control of the endoplasmic reticulum (ER) both as the site for protein handling (synthesis, folding, trafficking, disaggregation and degradation) and as a Ca2+ store is of crucial importance for correct functioning of the cell. Disturbance of the homeostatic control mechanisms leads to a vast array of severe pathologies. The Ca2+ content of the ER is a dynamic equilibrium between active uptake via Ca2+ pumps and Ca2+ release by a number of highly regulated Ca2+-release channels. Regulation of the Ca2+-release channels is very complex and several mechanisms are still poorly understood or controversial. There is increasing evidence that a number of unrelated proteins, either by themselves or in association with other Ca2+ channels, can provide additional Ca2+-leak pathways. The ER is a dynamic organelle and changes in its size and components have been described, either as a result of (de)differentiation processes affecting the secretory capacity of cells, or as a result of adaptation mechanisms to diverse stress conditions such as the unfolded protein response and autophagy. In this review we want to give an overview of the current knowledge of the (short-term) regulatory mechanisms that affect Ca2+-release and Ca2+-leak pathways and of the (long-term) adaptations in ER size and capacity. Understanding of the consequences of these mechanisms for cellular Ca2+ signaling could provide a huge therapeutic potential.

STIM and Orai proteins: players in sexual differences in hypertension-associated vascular dysfunction?

Sex-associated differences in hypertension have been observed repeatedly in epidemiological studies; however, the mechanisms conferring vascular protection to females are not totally elucidated. Sex-related differences in intracellular Ca(2+) handling or, more specifically, in mechanisms that regulate Ca(2+) entry into vascular smooth muscle cells have been identified as players in sex-related differences in hypertension-associated vascular dysfunction. Recently, new signalling components that regulate Ca(2+) influx, in conditions of intracellular store depletion, were identified: STIM1 (stromal interaction molecule 1), which works as an intracellular Ca(2+) sensor; and Orai1, which is a component of the CRAC (Ca(2+) release-activated Ca(2+)) channels. Together, these proteins reconstitute store-operated Ca(2+) channel function. Disturbances in STIM1/Orai1 signalling have been implicated in pathophysiological conditions, including hypertension. In the present article, we analyse evidence for sex-related differences in Ca(2+) handling and propose a new hypothesis where sex-related differences in STIM/Orai signalling may contribute to hypertension-associated vascular differences between male and female subjects.

Increased activation of stromal interaction molecule-1/Orai-1 in aorta from hypertensive rats: a novel insight into vascular dysfunction

Disturbances in the regulation of cytosolic calcium (Ca(2+)) concentration play a key role in the vascular dysfunction associated with arterial hypertension. Stromal interaction molecules (STIMs) and Orai proteins represent a novel mechanism to control store-operated Ca(2+) entry. Although STIMs act as Ca(2+) sensors for the intracellular Ca(2+) stores, Orai is the putative pore-forming component of Ca(2+) release-activated Ca(2+) channels at the plasma membrane. We hypothesized that augmented activation of Ca(2+) release-activated Ca(2+)/Orai-1, through enhanced activity of STIM-1, plays a role in increased basal tonus and vascular reactivity in hypertensive animals. Endothelium-denuded aortic rings from Wistar-Kyoto and stroke-prone spontaneously hypertensive rats were used to evaluate contractions because of Ca(2+) influx. Depletion of intracellular Ca(2+) stores, which induces Ca(2+) release-activated Ca(2+) activation, was performed by placing arteries in Ca(2+) free-EGTA buffer. The addition of the Ca(2+) regular buffer produced greater contractions in aortas from stroke-prone spontaneously hypertensive rats versus Wistar-Kyoto rats. Thapsigargin (10 micromol/L), an inhibitor of the sarcoplasmic reticulum Ca(2+) ATPase, further increased these contractions, especially in stroke-prone spontaneously hypertensive rat aorta. Addition of the Ca(2+) release-activated Ca(2+) channel inhibitors 2-aminoethoxydiphenyl borate (100 micromol/L) or gadolinium (100 micromol/L), as well as neutralizing antibodies to STIM-1 or Orai-1, abolished thapsigargin-increased contraction and the differences in spontaneous tone between the groups. Expression of Orai-1 and STIM-1 proteins was increased in aorta from stroke-prone spontaneously hypertensive rats when compared with Wistar-Kyoto rats. These results support the hypothesis that both Orai-1 and STIM-1 contribute to abnormal vascular function in hypertension. Augmented activation of STIM-1/Orai-1 may represent the mechanism that leads to impaired control of intracellular Ca(2+) levels in hypertension.

Nifedipine-sensitive noradrenergic vasoconstriction is enhanced in spontaneously hypertensive rats: the influence of chronic captopril treatment

AIM

The relationship between increased sympathetic tone and enhanced activity of L-type voltage-dependent Ca2+ channels (L-VDCC) in spontaneously hypertensive rats (SHR) was studied using in vivo and in vitro approaches.

METHODS

The effects of acute L-VDCC blockade on sympathetic vasoconstriction or blood pressure (BP) and the contribution of calcium influx to norepinephrine (NE)-induced arterial contraction were investigated in 10-week-old SHR and in age-matched SHR made normotensive by chronic captopril treatment from weaning.

RESULTS

Blood pressure fall occurring after acute ganglionic or L-VDCC blockade was enhanced in SHR. Ganglionic blockade eliminated strain differences in BP response to acute L-VDCC blockade and vice versa, suggesting that enhanced contribution of L-VDCC is responsible for augmented sympathetic vasoconstriction in SHR. Both phasic (dependent on internal calcium stores) and tonic (dependent on calcium influx) contractions to NE were augmented in SHR femoral arteries in vitro. Nifedipine attenuated only tonic contractions but to a larger extent in SHR than in WKY arteries. Nifedipine effect was greater after endothelium removal, which augmented tonic but not phasic contractions after NE. Chronic captopril treatment of SHR prevented hypertension development by suppression of their sympathetic vasoconstriction including its nifedipine-sensitive component, but failed to influence enhanced NE-induced arterial contractions or increased relaxation to nifedipine in vitro.

CONCLUSION

The contribution of nifedipine-sensitive component to noradrenergic vasoconstriction is enhanced during excessive NE stimulation (increased sympathetic tone of SHR in vivo or supramaximal NE stimulation in vitro). It seems that captopril-induced reduction of central sympathetic tone is able to normalize augmented nifedipine-sensitive vasoconstriction in SHR.

Three-dimensional culture of human uterine smooth muscle myocytes on a resorbable scaffolding

The objective of this study was to develop a three-dimensional culture system for the study of human myometrial physiology. Primary cell lines were initiated from human myometrium obtained at the time of term cesarean delivery. After several passages, cells were seeded onto a polyglactin-910 (Vicryl) mesh and maintained in culture. After several days in culture, each mesh was transferred to another culture dish and suspended to avoid contact with the plastic of the dish. Time-lapse videomicroscopy was used to observe cell proliferation and three-dimensional (3-D) fill of the pores of the mesh. Membrane potentials of the cells of this 3-D tissue were measured with a conventional microelectrode. Confocal microscopy was used to assess 3-D morphology. In some experiments, cells were seeded onto two layers of mesh and then cultured as described above. In this two-mesh experiment, force was measured by anchoring one mesh and pulling on the other, using a micrometer-driven strain gauge. In the single-mesh experiment, cells grew into and filled the pores of the mesh by repetitive proliferation, retraction, and proliferation. A confluent, 3-D tissue was obtained within 10 to 14 days of the initial seeding of the mesh. The average membrane potential of the cells within the single mesh was -35 +/- 6 mV. Confocal microscopy demonstrated tissue thickness of 9 to 40 microm (one to eight cells) within the pores of the mesh. In the two-mesh experiment, 2 to 3 weeks in culture yielded confluent 3-D tissues, in which myocytes not only filled the pores of each mesh, but also bridged between the two meshes. The bridging myocytes were able to maintain a tension of 5 g/cm(2) before separation of the two meshes, and coordinated contractions of 40 to 200 cells were observed. We conclude that cultured human myocytes proliferate and form 3-D tissues when supported by Vicryl scaffolding. Tissue grown in 3-D may provide a model system that is sufficient to probe the physiology of cell-to-cell interactions in myometrium.

Preservation of vascular contraction during ageing: dual effect on calcium handling and sensitization

(1) The present study was aimed to characterize the effects of ageing on vascular contraction by noradrenaline in rat isolated arteries. The existence of vascular bed heterogeneity was investigated in endothelium-denuded conductance (aorta) and resistance (small mesenteric artery, SMA) arteries, with respect to Ca(2+) handling, Ca(2+) sensitization or Ca(2+)-independent mechanisms. (2) In both arteries, contractions to noradrenaline were not different between adult and aged rats. (3) In Ca(2+)- free medium, noradrenaline elicited a transient increase in tension that was reduced by the Ca(2+) mobilizing agents, ryanodine and thapsigargin, in arteries from adult rats. A loss of the thapsigargin- but not the ryanodine-sensitive component of noradrenaline-induced contraction was observed in the two arteries from aged rats. (4) After depletion of Ca(2+) stores with noradrenaline, addition of exogenous CaCl(2) produced a sustained contraction that was decreased to the same extent by the protein kinase C inhibitor, GF 109203X and the tyrosine kinase inhibitor, tyrphostin A-23, in arteries from adult and aged rats. The Rho-associated protein kinase inhibitor, Y-27632, caused identical relaxation of noradrenaline pre-contracted arteries from both age groups. (5) Basal intracellular calcium ([Ca(2+)](i)) was higher in SMA from aged than from adult rats. In addition, the noradrenaline [Ca(2+)](i)-force relationship was significantly shifted to the right in the SMA from aged rats. (6) Altogether, these data indicate that responsiveness to noradrenaline is preserved both in conductance and resistance arteries with ageing. The latter results from the association of increased basal [Ca(2+)](i), changes in Ca(2+) handling at the level of thapsigargin-sensitive sarcoplasmic reticulum Ca(2+)-ATPases and decreased myofilament sensitivity to Ca(2+).

Ouabain-induced signaling and vascular smooth muscle cell proliferation

The hypothesis of this study is that the sodium pump complex acts as an intracellular signal-transducing molecule in canine vascular smooth muscle cells through its interaction with other membrane and cytoskeletal proteins. We have demonstrated that 1 nm ouabain induced transactivation of the epidermal growth factor receptor (EGFR), resulting in increased proliferation and bromodeoxyuridine (BrdUrd) uptake. Immunoprecipitation and Western blotting showed that the EGFR and Src were phosphorylated within 5 min of 10(-9) m ouabain stimulation. Both ouabain-induced DNA synthesis (BrdUrd uptake) and MAPK42/44 phosphorylation were inhibited by the Src inhibitor PP2, the EGFR kinase inhibitor AG1478, the tyrosine kinase inhibitor genistein, and the MEK1 inhibitor PD98059. Ouabain concentrations higher than 1 nm had little or no stimulating effect on proliferation or BrdUrd uptake but did minimally activate ERK1/2. Thus, low concentrations of ouabain, which do not inhibit the sodium pump sufficiently to perturb the resting cellular ionic milieu, initiate a transactivational signaling cascade leading to vascular smooth muscle cell proliferation.

Developmental changes in ryanodine- and IP(3)-sensitive Ca(2+) pools in ovine basilar artery

To explore the hypothesis that cerebrovascular maturation alters ryanodine- and inositol 1,4,5-trisphosphate (IP(3))-sensitive Ca(2+) pool sizes, we measured total intracellular Ca(2+) with (45)Ca and the fractions of intracellular Ca(2+) released by IP(3) and/or caffeine in furaptra-loaded permeabilized basilar arteries from nonpregnant adult and term fetal (139-141 days) sheep. Ca(2+) mass (nmol/mg dry weight) was similar in adult (1.60 +/- 0.18) and fetal (1.71 +/- 0.16) arteries in the pool sensitive to IP(3) alone but was significantly lower for adult (0.11 +/- 0.01) than for fetal (1.22 +/- 0.11) arteries in the pool sensitive to ryanodine alone. The pool sensitive to both ryanodine and IP(3) was also smaller in adult (0.14 +/- 0.01) than in fetal (0.85 +/- 0.08) arteries. Because the Ca(2+) fraction in the ryanodine-IP(3) pool was small in both adult (5 +/- 1%) and fetal (7 +/- 4%) arteries, the IP(3) and ryanodine pools appear to be separate in these arteries. However, the pool sensitive to neither IP(3) nor ryanodine was 10-fold smaller in adult (0.87 +/- 0.10) than in fetal (8.78 +/- 0.81) arteries, where it accounted for 72% of total intracellular membrane-bound Ca(2+). Thus, during basilar artery maturation, intracellular Ca(2+) mass plummets in noncontractile pools, decreases modestly in ryanodine-sensitive pools, and remains constant in IP(3)-sensitive pools. In addition, age-related increases in IP(3) efficacy must involve factors other than IP(3) pool size alone.

Norepinephrine-induced calcium signaling pathways in afferent arterioles of genetically hypertensive rats

This study provides new information about the relative importance of calcium mobilization and entry in the renal vascular response to adrenoceptor activation in afferent arterioles isolated from 7- to 8-wk-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Intracellular free calcium concentration ([Ca(2+)](i)) was measured in microdissected arterioles utilizing ratiometric photometry of fura 2 fluorescence. There was no significant strain difference in baseline [Ca(2+)](i). Norepinephrine (NE; 10(-6) and 10(-7) M) elicited immediate, sustained increases in [Ca(2+)](i). The general temporal pattern of response to 10(-6) M NE consisted of an initial peak and a maintained plateau phase. The response to NE was partially blocked by nifedipine (10(-6) M) or 8-(N,N-diethylamino) octyl-3,4,5-trimetoxybenzoate (TMB-8; 10(-5) M). A calcium-free external solution abolished the sustained [Ca(2+)](i) plateau response to NE, with less influence on the peak response. In the absence of calcium entry, TMB-8 (10(-5) M) completely blocked the calcium response to NE in WKY but not SHR, suggesting strain differences in mobilization. A higher concentration of TMB-8 (10(-4) M), however, blocked all discernible mobilization in both strains. We conclude that there are differences in Ca(2+) handling in renal resistance vessels between young WKY and SHR with respect to mobilization stimulated by alpha-adrenoceptors. Afferent arterioles of young SHR appear to have a larger inositol-1,4,5-trisphosphate-sensitive pool or release from a site less accessible to TMB-8.

SERCA function declines with age in adrenergic nerves from the superior cervical ganglion

1. Intracellular calcium is a universal second messenger integrating numerous cellular pathways. An age-related breakdown in the mechanisms controlling [Ca2+]i homeostasis could contribute to neuronal degeneration. One component of neuronal calcium regulation believed to decline with age is the function of sarco/endoplasmic reticulum calcium ATPase (SERCA) pumps. 2. Therefore we investigated the impact of age on the capacity of SERCA pumps to control high (68 mM) [K+]-evoked [Ca2+]i-transients in acutely dissociated superior cervical ganglion (SCG) cells from 6- and 20-month-old Fisher-344 rats. Calcium transients were measured by fura-2 microfluorometry in the presence of vanadate (0.1 microM) to selectively block plasma membrane calcium ATPase (PMCA) pumps, dinitrophenol (100 microM) to block mitochondrial calcium uptake and extracellular sodium replaced with tetraethylammonium to block Na+/Ca2+-exchanger, thus forcing the neuronal cells to rely on SERCA uptake to control [Ca2+]i homeostasis. 3. In the presence of these calcium buffering blockers, the rate of recovery of [Ca2+]i was significantly slower and time to recover to approximately 90% of resting [Ca2+]i was significantly greater in SCG cells from old (20 months) compared with young (6 months) animals. 4. This age-related change in the recovery phase of [K+]-evoked [Ca2+]i-transients could not be explained by differences in the sensitivity of SCG cells to the calcium buffering blockers, as no age-related difference in basal [Ca2+]i was observed. 5. These studies illustrate that when rat SCG cells are forced to rely on SERCAs to buffer [K+]-evoked [Ca2+]i-transients, an age-related decline in SERCA function is revealed. Such age-related declines in calcium regulation coupled with neuronal sensitivity to calcium overload underscore the importance of understanding the components of [Ca2+]i homeostasis and the functional compensation that may occur with advancing age.