Vascular Smooth Muscle Contractility Research Articles

The pro‐apoptotic protein Par‐4 facilitates vascular contractility by cytoskeletal targeting of ZIPK

Par-4 (prostate apoptosis response 4) is a pro-apoptotic protein and tumour suppressor that was originally identified as a gene product up-regulated during apoptosis in prostate cancer cells. Here, we show, for the first time, that Par-4 is expressed and co-localizes with the actin filament bundles in vascular smooth muscle. Furthermore, we demonstrate that targeting of ZIPK to the actin filaments, as observed upon PGF-2α stimulation, is inhibited by the presence of a cell permeant Par-4 decoy peptide. The same decoy peptide also significantly inhibits PGF-2α induced contractions of smooth muscle tissue. Moreover, knockdown of Par-4 using antisense morpholino nucleotides results in significantly reduced contractility, and myosin light chain and myosin phosphatase target subunit phosphorylation. These results indicate that Par-4 facilitates contraction by targeting ZIPK to the vicinity of its substrates, myosin light chain and MYPT, which are located on the actin filaments. These results identify Par-4 as a novel regulator of myosin light chain phosphorylation in differentiated, contractile vascular smooth muscle.

Krüppel-Like Factor 4

See related article, pages 1548–1557 The transcriptional response to vascular injury. The vascular response to injury is a dynamic and multifactorial process involving several cell types. As part of the vascular response to injury, normally quiescent, contractile vascular smooth muscle cells (VSMCs) respond to inflammatory and growth factors by transforming from a differentiated contractile state to a dedifferentiated synthetic phenotype capable of migration, proliferation, and synthesis of cytokines and extracellular matrix.1 As the major effector cell in this occlusive process, the VSMC must coordinate and synchronize immensely complex inflammatory, proliferative, and differentiation programs. Indeed, the activated “myofibroblastic” VSMCs can even express proteins and cytokines ascribed to be restricted to inflammatory cells.2,3 Several transcription factors have earned the moniker of “master switch” of inflammation (eg, NF-κB), or proliferation (eg, Egr-1), or differentiation (eg, myocardin).4–6 Is it possible, or even plausible, from a cellular standpoint, that a single transcription factor could potentially play an important part in all 3 of these processes? The Kruppel-like family of transcription factors contain zinc finger DNA binding domains and presently include at least 16 mammalian members,7 with several having important roles in cardiovascular pathophysiology.8 One might think that there would be redundancy among so many family members; however, the non–zinc finger domain of these transcription factors displays structural heterogeneity, resulting in surprising functional diversity among Kruppel proteins.9 In particular, the role of Kruppel-like factor (KLF)4 in vascular biology and the mechanisms of its effects are as complex as the cells that participate in vascular disease are diverse. For example, in macrophages, KLF4 is induced by inflammatory stimuli and mediates induction of proinflammatory genes by 2 different, but complementary, mechanisms. In the first, KLF4 interacts with the NF-κB subunit p65 and cooperates with its transactivation of proinflammatory genes. In the …

Phosphoinositide 3‐kinase contributes to diabetes‐induced abnormal vascular reactivity in rat perfused mesenteric bed

Phosphatidylinositol 3-kinase (PI3K) is a signaling enzyme that plays key roles in vascular growth, proliferation, and cellular apoptosis and is implicated in modulating vascular smooth muscle contractility. The aim of this study was to determine whether PI3K contributes to development of diabetes-induced abnormal vascular reactivity to selected vasoactive agonists. The effect of 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), a selective PI3K inhibitor, on isolated perfused mesenteric vascular bed from streptozotocin (STZ)-diabetic rats was investigated. Changes in perfusion pressure, which reflected peripheral resistance, were measured using isolated perfused mesenteric vascular beds. Our results showed that STZ treatment produced an increase in the vasoconstrictor response to norepinephrine (NE), angiotensin II (Ang II) and endothelin-1 (ET-1), and an attenuated vasodilator response to carbachol and histamine in the isolated perfused mesenteric vascular bed from STZ-diabetic animals. Chronic inhibition of PI3K with LY294002 resulted in prevention of diabetes-induced abnormal vascular reactivity to the vasoactive agonists. However, the high blood glucose levels were not normalized. Results of this study indicate that selective inhibition of PI3K can attenuate the development of diabetes-induced abnormal vascular responsiveness in the isolated perfused mesenteric vascular bed.

Blockade of Chronic High Glucose–Induced Endothelial Apoptosis bySasa borealisBamboo Extract

Hyperglycemia is a causal factor in the development of diabetic vascular complications including impaired vascular smooth muscle contractility and increased cell proliferation. The present study was designed to investigate the effects of Sasa borealis water-extract (SBwE) on chronic hyperglycemia-induced oxidative stress and apoptosis in human umbilical endothelial cells (HUVEC). HUVEC were cultured in 5.5 mM low glucose, 5.5 mM glucose plus 27.5 mM mannitol as an osmotic control, or 33 mM high glucose for 5 days in the absence and presence of 1-30 microg/ ml SBwE. Caspase-3 activation and Annexin V staining revealed chronic high glucose-induced endothelial apoptotic toxicity with a generation of oxidants detected by DCF-fluorescence, and these effects were reversed by SBwE at > or =1 microg/ml in a dose-dependent manner. Cytoprotective SBwE substantially reduced the sustained high glucose-induced expression of endothelial nitric oxide synthase and attenuated the formation of peroxynitrite radicals. The suppressive effects of SBwE were most likely mediated through blunting activation of PKC beta 2 and NADPH oxidase promoted by high glucose. In addition, this bamboo extract modulated the high glucose-triggered mitogen-activated protein kinase-dependent upregulation of heat-shock proteins. Our results suggest that SBwE suppressed these detrimental effects caused by PKC-dependent peroxynitrite formation via activation of NADPH oxidase and induction of nitric oxide synthase and heat-shock protein family that may be essential mechanisms responsible for increased apoptotic oxidative stress in diabetic vascular complications. Moreover, the blockade of high glucose-elicited heat-shock protein induction appeared to be responsible for SBwE-alleviated endothelial apoptosis. Therefore, SBwE may be a therapeutic agent for the prevention and treatment of diabetic endothelial dysfunction and related complications.

EFEK 17β-ESTRADIOL TERHADAP DENSITAS RESEPTOR ADRENERGIK-αIDDAN KONTRAKTILITAS OTOT POLOS PEMBULUH DARAH TIKUS

The incidence of hypertension in menopausal and post menopausal women related to plasma estrogen leveland sympathetic nervous activity. Estrogen may have a specific effect to modulate adrenergic vasoconstriction by modulating adrenergic receptors. Blood vessels contractility is regulated mainly by the sympathetic nervous system, in aorta mediated particularly by  α1Dadrenergic receptor.We hypothesize that 17βestradiol decreases vascular smooth muscle contractility by decreasing  α1Dadrenergic receptor density. To prove the above mechanism in the present study we performed several interrelated assays, i.e bioassay using isolated organ and protein blotting. An isolated rat aortic ring without endothelium (2-3 month,150-200 gram) was incubated in 17β-estradiol (10-5M, 10-4M,and 10-3M ) for two hours prior to stimulation using phenylephrine as α1Dadrenergic receptor agonist. The response of the rat aortic ring to the stimulation of α1Dadrenergic receptor agonist was measured as the subsequent change on aortic contractility using bioassay, and the change of  α1Dadrenergic receptor density using Western and dotblot.

Transduction of recombinant heat shock protein 27 increases contractility of vascular smooth muscle

Heat shock protein 27 (HSP27) is a stress induced cytoprotective protein, which has been shown be involved in contraction, stress fiber formation, and reorganization of actin cytoskeleton. In this study, the role of HSP27 on contractility in rat aortic vascular smooth muscle (VSM) tissue was examined by using a transducible recombinant HSP27 (rPTDHSP27). Human HSP27 cDNA, that was fused with a protein transduction domain and 6x Histidine tag at the N terminal end, was expressed in Escherichia coli and purified using a metal chelating affinity column. The purified protein was verified through Western blot and HPLC ESI MS/MS. VSM rings were equilibrated in a muscle bath, and contracted with norepinephrine (NE) (1–1000 nM) with or without 3.8 μM rPTDHSP27 and force generated was measured. Norepinephrine induced a dose dependent contraction, which was enhanced with the pretreatment of rPTDHSP27 (84.1% compared to 16.9% in the control with 16 nM NE). The concentration needed to produce maximal contraction was 10 fold lower when the tissue was pretreated with rPTDHSP27 (88% at 666 nM compared to 96% at 66 nM, for control and rPTDHSP27 treated rings respectively). NIH RO1 70715

DOES PERIVASCULAR FAT MODULATE CORONARY ARTERY CONTRACTILITY?

Adipose tissue is reported to modulate contractility in vascular smooth muscle, via a postulated relaxing factor (ADRF) derived from adipocytes. We studied pig LAD coronary arteries with or without endothelium (+/−E) and/or fat (+/−F). +E preparations produced greater forces (P<0.05), whereas +F preparations reduced force for KCl, Histamine and U46619, but not for ACh. The effects of fat were concentration‐dependent for +E and greatest at submax [U46619]. A role for endothelin‐1 was tested with U46619, using an ET receptor antagonist, PD145065 (1 μM). The COX inhibition with indomethacin (1E‐5M) was used to test for potential ADRF's. There were no changes in force after PD145065. Relaxation to indomethacin was also similar in endothelial and de‐endothelialized LAD, suggesting eicosanoids are not involved. Indomethacin significantly relaxed all LAD, but there was marked decrease in relaxation by LAD with fat indicating a potential prostanoid nature for ADRF. Our data suggest the presence of both an endothelial constricting factor and an ADRF and interactions between adipose tissue and the endothelium. Supported by AHA 0655300B and NIH HL61974(RJP).

Effects of benzocaine on vascular smooth muscle contractility of the sea lamprey dorsal aorta

Benzocaine is a common fish anesthetic. This experiment was undertaken in order to determine the action of benzocaine and the mechanisms of action of calcium in the vascular smooth muscle from the dorsal aorta (LDA) of sea lamprey (Petromyzon marinus). Benzocaine contracted otherwise unstimulated vessels and vessels precontracted with either norepinephrine (NE) or KCl in a dose dependent manner. The vehicle, ethanol, also effected contraction in a dose dependent manner. LDA contracted significantly more when exposed to benzocaine in ethanol than to an equal volume of ethanol alone. LDA stimulated with NE were significantly more sensitive to benzocaine than were either unstimulated LDA or in LDA precontracted with KCl. LDA stimulated with KCl contracted significantly less in the absence of extracellular (EC) Ca2+ but the contractions doubled when EC Ca2+ was added back. Ethanol contractions were insignificant in the absence of EC Ca2+. Benzocaine‐induced contractions of LDA treated with thapsigargin and caffeine were significantly reduced in both the presence and absence of EC Ca2+. Therefore, KCl− and ethanol‐induced contractions were found to be dependent upon EC Ca2+ entry, while benzocaine was dependent upon intracellular Ca2+, most likely from the sarcoplasmic reticulum. These are important considerations to take into account when anesthetizing fish, particularly cyclostomes.

Expression Levels of mRNA for Rho A/Rho Kinase and Its Role in Isoprostane-Induced Vasoconstriction of Human Placental and Maternal Vessels

Preeclampsia is characterized by intense and prolonged vasoconstriction. Rho A-mediated calcium sensitization is central to prolonged contractility of vascular smooth muscle. The aims of this study are (1) to investigate mRNA expression levels of Rho A/Rho kinases in placental tissues from normotensive and preeclamptic women and (2) to investigate the effects of 2 isoprostanes, 8-iso prostaglandin F(2)( alpha) (8-iso PGF(2 alpha) ) and 8-iso prostaglandin E(2) (8-iso PGE(2)), on small placental and myometrial vessel resistance and to determine if their effects were mediated via the Rho kinase pathway. Real-time reverse transcription polymerase chain reaction for Rho A, ROCK I, and ROCK II was performed on total RNA from normotensive and preeclamptic placentae. The effects of 8- iso PGF(2 alpha) and 8-iso PGE(2) (alone and with the specific Rho kinase inhibitor Y-27632) on placental and myometrial vessels (<400 microm) were measured and compared with control recordings. Rho A mRNA expression levels were significantly higher in placentae from preeclamptic women than in placentae from normotensive women (P < .01). There was no significant difference in expression levels of ROCK I and ROCK II between both tissue types (P > .05). Both isoprostanes exerted a significant concentration-dependent vasocontractile effect on both vessel types (P < .001). This effect was antagonized by Y-27632 in placental arteries but not in myometrial arteries. Increased Rho A mRNA expression in placentae from preeclamptic women is suggestive of a role for the Rho kinase pathway in the modulation of the placental vasculature in this condition. Isoprostanes exert their vasocontractile effect, in placental vasculature, in part via the Rho kinase pathway.

CGMP-Dependent Protein Kinase I and Smooth Muscle Relaxation

See related article, pages 1096–1103 The maintenance of vascular tone is central to the regulation of blood pressure and tissue perfusion and plays a role in the pathogenesis of hypertension and atherosclerosis. Vascular tone is determined by the balance of vasodilator and vasoconstrictor stimuli. After several decades of research, the NO/cGMP/cGMP-dependent protein kinase (cGK) pathway is now recognized as an important mediator of vasodilation. However, the mechanisms by which cGK causes smooth muscle relaxation continue to be an important question. Smooth muscle contraction and relaxation are tightly coupled to the phosphorylation and dephosphorylation, respectively, of the regulatory myosin light chain.1 Myosin light chain phosphorylation state is determined by the relative activities of myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP). MLCK phosphorylates MLC leading to contraction,2 and MLCP dephosphorylates MLC, leading to relaxation3 (Figure). Both MLCK and MLCP activities are highly regulated. MLCK activity is activated by the binding of calcium/calmodulin and thus is the primary mechanism linking intracellular calcium concentration to smooth muscle contractility.4 MLCP activity is regulated by both vasodilator and vasoconstrictor stimuli, and is therefore responsible for much of the calcium-independent regulation of contractility (reviewed in5). Figure. MLC phosphorylation determines smooth muscle contractility. Contractile agonists lead to inositol 1,4,5 triphosphate (IP3) production or activation of RhoA (RhoA-GTP). IP3 binding to its receptor in the sarcoplasmic reticulum leads to release of Ca2+. Ca2+/calmodulin binds to and activates MLCK, which in turn phosphorylates MLC (calcium-dependent contraction). Activated RhoA binds to and activates ROCK, leading to phosphorylation and inhibition of MLCP, inhibiting MLC dephosphorylation (calcium-independent contraction). cGKI mediates relaxation by inhibiting both calcium-dependent and -independent contraction. cGKIα activates MLCP by a direct interaction and by inhibition of RhoA, and activates RGS2 to inhibit Gαq …

Effects of pioglitazone and rosiglitazone on aortic vascular function in rat genetic hypertension

Glitazones have beneficial antihypertensive effects independent of their insulin-sensitizing action. We have studied the effects of pioglitazone and rosiglitazone on the endothelial ability to counteract vascular smooth muscle contractility in genetic hypertension. To achieve this, we measured isometric responses of aortic segments obtained from spontaneously hypertensive rats. The effects of glitazones on endothelial function were studied by assessing the endothelial modulation of phenylephrine-induced isometric contractions (10 − 9 –10 − 5 M) in the presence or absence of pioglitazone or rosiglitazone (10 − 5 M), added directly to an organ bath or orally administered to the rats (pioglitazone, 10 mg/kg). The role of both NO and prostanoids was analyzed by performing experiments in the presence of N G-nitro- l-arginine methyl ester ( l-NAME) and/or indomethacin (both 10 − 5 M) in the organ bath. Concentration-dependent contractions to l-NAME (10 − 6 –3 × 10 − 4 M) in the presence or absence of glitazones were carried out as an estimation of basal NO release. Pioglitazone, but not rosiglitazone, increased contractile responses to phenylephrine in intact vessels. The contractile responses to phenylephrine obtained in the presence of glitazones were markedly diminished by indomethacin, but enhanced by l-NAME. Analogous results were obtained in aortas from pioglitazone-chronically treated animals. l-NAME concentration-dependent contractions were enhanced by both glitazones. Both glitazones lowered the sensitivity to acetylcholine (10 − 9 –10 − 5 M). In conclusion, pioglitazone and rosiglitazone alter vascular function differentially and through endothelium-dependent mechanisms. These drugs act over the same pathways on the endothelium where they have a dual action, increasing both production of vasoconstrictor prostanoids and NO. The balance between both vasoactive substances determines the vascular response to glitazones.

The dopaminergic system in hypertension

Dopamine plays an important role in the pathogenesis of hypertension by regulating epithelial sodium transport, vascular smooth muscle contractility and production of reactive oxygen species and by interacting with the renin-angiotensin and sympathetic nervous systems. Dopamine receptors are classified into D(1)-like (D(1) and D(5)) and D(2)-like (D(2), D(3) and D(4)) subtypes based on their structure and pharmacology. Each of the dopamine receptor subtypes participates in the regulation of blood pressure by mechanisms specific for the subtype. Some receptors regulate blood pressure by influencing the central and/or peripheral nervous system; others influence epithelial transport and regulate the secretion and receptors of several humoral agents. This review summarizes the physiology of the different dopamine receptors in the regulation of blood pressure, and the relationship between dopamine receptor subtypes and hypertension.

Vascular development in early ovine gestation: carotid smooth muscle function, phenotype, and biochemical markers

Vascular smooth muscle (VSM) maturation is developmentally regulated and differs between vascular beds. The maturation and contribution of VSM function to tissue blood flow and blood pressure regulation during early gestation are unknown. The carotid artery (CA) contributes to fetal cerebral blood flow regulation and well being. We studied CA VSM contractility, protein contents, and phenotype beginning in the midthird of ovine development. CAs were collected from early (88-101 day of gestation) and late (138-150 day; term = day 150) fetal (n = 14), newborn (6-8 day old; n = 7), and adult (n = 5) sheep to measure forces in endothelium-denuded rings with KCl, phenylephrine, and ANG II; changes in cellular proteins, including total and soluble protein, actin and myosin, myosin heavy chain isoforms (MHC), filamin, and proliferating cell nuclear antigen; and vascular remodeling. KCl and phenylephrine elicited age- and dose-dependent contraction responses (P < 0.001) at all ages except early fetal, which were unresponsive. In contrast, ANG II elicited dose responses only in adults, with contractility increasing greater than fivefold vs. that shown in fetal or neonatal animals (P < 0.001). Increased contractility paralleled age-dependent increases (P < 0.01) in soluble protein, actin and myosin, filamin, adult smooth muscle MHC-2 (SM2) and medial wall thickness and reciprocal decreases (P < 0.001) in nonmuscle MHC-B, proliferating cell nuclear antigen and medial cellular density. VSM nonreceptor- and receptor-mediated contractions are absent or markedly attenuated in midgestation and increase age dependently, paralleling the transition from synthetic to contractile VSM phenotype and, in the case of ANG II, paralleling the switch to the AT(1) receptor. The mechanisms regulating VSM maturation and thus blood pressure and tissue perfusion in early development remain to be determined.

Transgenic mice expressing Na+-K+-ATPase in smooth muscle decreases blood pressure

The Na(+)-K(+)-ATPase (NKA) is a transmembrane protein that sets and maintains the electrochemical gradient by extruding three Na(+) in exchange for two K(+). An important physiological role proposed for vascular smooth muscle NKA is the regulation of blood pressure via modulation of vascular smooth muscle contractility (5). To investigate the relations between the level of NKA in smooth muscle and blood pressure, we developed mice carrying a transgene for either the NKA alpha(1)- or alpha(2)-isoform (alpha(1 sm+) or alpha(2 sm+) mice) driven by the smooth muscle-specific alpha-actin promoter SMP8. Interestingly, both alpha-isoforms, the one contained in the transgene and the one not contained, were increased to a similar degree at both protein and mRNA levels. The total alpha-isoform protein was increased from 1.5-fold (alpha(1 sm+) mice) to 7-fold (alpha(2 sm+) mice). The increase in total NKA alpha-isoform protein was accompanied by a 2.5-fold increase in NKA activity in alpha(2 sm+) gastric antrum. Immunocytochemistry of the alpha(1)- and alpha(2)-isoforms in alpha(2 sm+) aortic smooth muscle cells indicated that alpha-isoform distributions were similar to those shown in wild-type cells. alpha(2 sm+) Mice (high expression) were hypotensive (109.9 +/- 1.6 vs. 121.3 +/- 1.4 mmHg; n = 13 and 11, respectively), whereas alpha(1 sm+) mice (low expression) were normotensive (122.7 +/- 2.5 vs. 117.4 +/- 2.3; n = 11 or 12). alpha(2 sm+) Aorta, but not alpha(1 sm+) aorta, relaxed faster from a KCl-induced contraction than wild-type aorta. Our results show that smooth muscle displays unique coordinate expression of the alpha-isoforms. Increasing smooth muscle NKA decreases blood pressure and is dependent on the degree of increased alpha-isoform expression.

Coupling a change in intraluminal pressure to vascular smooth muscle depolarization: still stretching for an explanation

pressure-induced (myogenic) constriction of arterioles is believed to be a fundamental contributor to the local regulation of microvascular blood flow and pressure. Myogenic constriction provides a level of tone upon which vasodilators can act to lower resistance and match blood flow to metabolic

Evidence of vascular smooth muscle contractile dysfunction in hereditary dilated cardiomyopathy

Aims: Cardiomyopathy in progressive muscular dystrophy (MD) has been suggested to be associated with concomitant alterations in vascular smooth muscle contractility. For the first time, we analyzed the contractile function of smooth muscle in inherited dilated cardiomyopathy using a mouse model.

Effects of inhibition of the Na+/K+/2Cl− cotransporter on myogenic and angiotensin II responses of the rat afferent arteriole

The Na(+)/K(+)/2Cl(-) cotransporter (NKCC) plays diverse roles in the kidney, contributing sodium reabsorption and tubuloglomerular feedback (TGF). However, NKCC is also expressed in smooth muscle and inhibitors of this transporter affect contractility in both vascular and nonvascular smooth muscle. In the present study, we investigated the effects of NKCC inhibitors on vasoconstrictor responses of the renal afferent arteriole using the in vitro perfused hydronephrotic rat kidney. This preparation has no tubules and no TGF, eliminating this potential complication. Furosemide and bumetanide inhibited myogenic responses in a concentration-dependent manner. Bumetanide was approximately 20-fold more potent (IC(50) 1.0 vs. 20 micromol/l). At 100 and 10 micromol/l, furosemide and bumetanide inhibited myogenic responses by 72 +/- 4 and 68 +/- 5%, respectively. The maximal level of inhibition by bumetanide was not affected by nitric oxide synthase inhibition (100 micromol/l N(G)-nitro-l-arginine methyl ester). However, the time course for the dilation was slowed (from t(1/2) = 4.0 +/- 0.5 to 8.3 +/- 1.7 min, P = 0.04), suggesting either a partial involvement of NO or a permissive effect of NO on relaxation kinetics. Bumetanide also inhibited ANG II-induced afferent arteriolar vasconstriction at similar concentrations. Finally, NKCC1, but not NKCC2, expression was demonstrated in the afferent arteriole by RT-PCR and the presence of NKCC1 in afferent arteriolar myocytes was confirmed by immunohistochemistry. In concert, these results indicate that NKCC modulation is capable of altering myogenic responses by a mechanism that does not involve TGF and suggest a potential role of NKCC1 in the regulation of vasomotor function in the renal microvasculature.

Smoothelin-B is essential for functional vascular smooth muscle contractility

Smoothelin-B is essential for functional vascular smooth muscle contractility

Defining the BK channel domains required for β1-subunit modulation

In a wide variety of cell types, including neurons and smooth muscle cells, activation of the large-conductance voltage- and Ca(2+)-activated K(+) (BK) channels causes transient membrane hyperpolarization, thereby regulating cellular excitability. Similar to other voltage-gated ion channels, BK channels, a tetramer of alpha-subunits, associate with auxiliary beta-subunits in a tissue-specific manner, modifying the channel's gating properties. The BK beta1-subunit, which is expressed in smooth muscle, increases the apparent Ca(2+) sensitivity (marked by a hyperpolarizing shift in the conductance-voltage relationship at a given Ca(2+) concentration), slows macroscopic activation and deactivation, and is required for channel activation by 17beta-estradiol. The beta1-subunit is essential for normal regulation of vascular smooth muscle contractility and blood pressure. Little is known, however, about the molecular mechanisms of beta1-subunit modulation of alpha-subunits. Here we show that the beta1-subunit's modulation of the Ca(2+) and 17beta-estradiol sensitivities can be dissociated from its effects on gating kinetics by truncation of the alpha-subunit's extracellular N-terminal residues. The BK alpha-subunit N terminus interacts uniquely with the beta1-subunit: beta2 regulation of the alpha-subunit is unaltered by truncation of the N terminus. Although the functional interaction of alpha and beta1 requires the N-terminal tail of alpha, the physical association requires the S1, S2, and S3 transmembrane helices of alpha.

HEAT SHOCK‐INDUCED AUGMENTATION OF VASCULAR CONTRACTILITY IS INDEPENDENT OF RHO‐KINASE

In a previous study, we demonstrated that heat shock augments the contractility of vascular smooth muscle through the stress response. 2. In the present study, we investigated whether Rho-kinases play a role in heat shock-induced augmentation of vascular contractility in rat isolated aorta. 3. Rat aortic strips were mounted in organ baths, exposed to 42 C for 45 min and subjected to contractile or relaxant agents 5 h later. 4. The level of expression of Rho-kinases in heat shock-exposed tissues was no different to that of control tissues, whereas heat shock induced heat shock protein (Hsp) 72 at 3 and 5 h. Heat shock resulted in an increase in vascular contractility in response to phenylephrine 5 h later. 5. The Rho-kinase inhibitors Y27632 (30 nmol/L-10 mmol/L) or HA 1077 (10 nmol/L-10 mmol/L) relaxed 1.0 mmol/L phenylephrine-precontracted vascular strips in a concentration-dependent manner; these effects were attenuated in heat shock-exposed strips. Pretreatment with Y27632 resulted in greater inhibition of the maximum contraction in control strips compared with those in heat shock-exposed strips. 6. The results of the present study suggest that Rho-kinases are unlikely to be involved in heat shock-induced augmentation of vascular contractility.