9-Phenanthrol inhibits recombinant and arterial myocyte TMEM16A channels

BACKGROUND AND PURPOSE

In arterial smooth muscle cells (myocytes), intravascular pressure stimulates membrane depolarization and vasoconstriction (the myogenic response). Ion channels proposed to mediate pressure-induced depolarization include several transient receptor potential (TRP) channels, including TRPM4, and transmembrane protein 16A (TMEM16A), a Ca(2+) -activated Cl(-) channel (CaCC). 9-Phenanthrol, a putative selective TRPM4 channel inhibitor, abolishes myogenic tone in cerebral arteries, suggesting that either TRPM4 is essential for pressure-induced depolarization, upstream of activation of other ion channels or that 9-phenanthrol is non-selective. Here, we tested the hypothesis that 9-phenanthrol is also a TMEM16A channel blocker, an ion channel for which few inhibitors have been identified.

EXPERIMENTAL APPROACH

Patch clamp electrophysiology was used to measure rat cerebral artery myocyte and human recombinant TMEM16A (rTMEM16A) currents or currents generated by recombinant bestrophin-1, another Ca(2+) -activated Cl(-) channel, expressed in HEK293 cells.

KEY RESULTS

9-Phenanthrol blocked myocyte TMEM16A currents activated by either intracellular Ca(2+) or Eact , a TMEM16A channel activator. In contrast, 9-phenanthrol did not alter recombinant bestrophin-1 currents. 9-Phenanthrol reduced arterial myocyte TMEM16A currents with an IC50 of ∼12 μM. Cell-attached patch recordings indicated that 9-phenanthrol reduced single rTMEM16A channel open probability and mean open time, and increased mean closed time without affecting the amplitude.

CONCLUSIONS AND IMPLICATIONS

These data identify 9-phenanthrol as a novel TMEM16A channel blocker and provide an explanation for the previous observation that 9-phenanthrol abolishes myogenic tone when both TRPM4 and TMEM16A channels contribute to this response. 9-Phenanthrol may be a promising candidate from which to develop TMEM16A channel-specific inhibitors.

An elevation in physical coupling of type 1 inositol 1,4,5-trisphosphate (IP3) receptors to transient receptor potential 3 (TRPC3) channels constricts mesenteric arteries in genetic hypertension

Hypertension is associated with an elevation in agonist-induced vasoconstriction, but mechanisms involved require further investigation. Many vasoconstrictors bind to phospholipase C-coupled receptors, leading to an elevation in inositol 1,4,5-trisphosphate (IP(3)) that activates sarcoplasmic reticulum IP(3) receptors. In cerebral artery myocytes, IP(3) receptors release sarcoplasmic reticulum Ca(2+) and can physically couple to canonical transient receptor potential 3 (TRPC3) channels in a caveolin-1-containing macromolecular complex, leading to cation current activation that stimulates vasoconstriction. Here, we investigated mechanisms by which IP(3) receptors control vascular contractility in systemic arteries and IP(3)R involvement in elevated agonist-induced vasoconstriction during hypertension. Total and plasma membrane-localized TRPC3 protein was ≈2.7- and 2-fold higher in mesenteric arteries of spontaneously hypertensive rats (SHRs) than in Wistar-Kyoto (WKY) rat controls, respectively. In contrast, IP(3)R1, TRPC1, TRPC6, and caveolin-1 expression was similar. TRPC3 expression was also similar in arteries of pre-SHRs and WKY rats. Control, IP(3)-induced and endothelin-1 (ET-1)-induced fluorescence resonance energy transfer between IP3R1 and TRPC3 was higher in SHR than WKY myocytes. IP3-induced cation current was ≈3-fold larger in SHR myocytes. Pyr3, a selective TRPC3 channel blocker, and calmodulin and IP(3) receptor binding domain peptide, an IP(3)R-TRP physical coupling inhibitor, reduced IP(3)-induced cation current and ET-1-induced vasoconstriction more in SHR than WKY myocytes and arteries. Thapsigargin, a sarcoplasmic reticulum Ca(2+)-ATPase blocker, did not alter ET-1-stimulated vasoconstriction in SHR or WKY arteries. These data indicate that ET-1 stimulates physical coupling of IP(3)R1 to TRPC3 channels in mesenteric artery myocytes, leading to vasoconstriction. Furthermore, an elevation in IP(3)R1 to TRPC3 channel molecular coupling augments ET-1-induced vasoconstriction during hypertension.

TMEM16A/ANO1 channels contribute to the myogenic response in cerebral arteries

RATIONALE

Pressure-induced arterial depolarization and constriction (the myogenic response) is a smooth muscle cell (myocyte)-specific mechanism that controls regional organ blood flow and systemic blood pressure. Several different nonselective cation channels contribute to pressure-induced depolarization, but signaling mechanisms involved are unclear. Similarly uncertain is the contribution of anion channels to the myogenic response and physiological functions and mechanisms of regulation of recently discovered transmembrane 16A (TMEM16A), also termed Anoctamin 1, chloride (Cl(-)) channels in arterial myocytes.

OBJECTIVE

To investigate the hypothesis that myocyte TMEM16A channels control membrane potential and contractility and contribute to the myogenic response in cerebral arteries.

METHODS AND RESULTS

Cell swelling induced by hyposmotic bath solution stimulated Cl(-) currents in arterial myocytes that were blocked by TMEM16A channel inhibitory antibodies, RNAi-mediated selective TMEM16A channel knockdown, removal of extracellular calcium (Ca(2+)), replacement of intracellular EGTA with BAPTA, a fast Ca(2+) chelator, and Gd(3+) and SKF-96365, nonselective cation channel blockers. In contrast, nimodipine, a voltage-dependent Ca(2+) channel inhibitor, or thapsigargin, which depletes intracellular Ca(2+) stores, did not alter swelling-activated TMEM16A currents. Pressure-induced (-40 mm Hg) membrane stretch activated ion channels in arterial myocyte cell-attached patches that were inhibited by TMEM16A antibodies and were of similar amplitude to recombinant TMEM16A channels. TMEM16A knockdown reduced intravascular pressure-induced depolarization and vasoconstriction but did not alter depolarization-induced (60 mmol/L K(+)) vasoconstriction.

CONCLUSIONS

Membrane stretch activates arterial myocyte TMEM16A channels, leading to membrane depolarization and vasoconstriction. Data also provide a mechanism by which a local Ca(2+) signal generated by nonselective cation channels stimulates TMEM16A channels to induce myogenic constriction.

Dynamic micro- and macrovascular remodeling in coronary circulation of obese Ossabaw pigs with metabolic syndrome

Previous studies from our laboratory showed that coronary arterioles from type 2 diabetic mice undergo inward hypertrophic remodeling and reduced stiffness. The aim of the current study was to determine if coronary resistance microvessels (CRMs) in Ossabaw swine with metabolic syndrome (MetS) undergo remodeling distinct from coronary conduit arteries. Male Ossabaw swine were fed normal (n = 7, Lean) or hypercaloric high-fat (n = 7, MetS) diets for 6 mo, and then CRMs were isolated and mounted on a pressure myograph. CRMs isolated from MetS swine exhibited decreased luminal diameters (126 ± 5 and 105 ± 9 μm in Lean and MetS, respectively, P < 0.05) with thicker walls (18 ± 3 and 31 ± 3 μm in Lean and MetS, respectively, P < 0.05), which doubled the wall-to-lumen ratio (14 ± 2 and 30 ± 2 in Lean and MetS, respectively, P < 0.01). Incremental modulus of elasticity (IME) and beta stiffness index (BSI) were reduced in CRMs isolated from MetS pigs (IME: 3.6 × 10(6) ± 0.7 × 10(6) and 1.1 × 10(6) ± 0.2 × 10(6) dyn/cm(2) in Lean and MetS, respectively, P < 0.001; BSI: 10.3 ± 0.4 and 7.3 ± 1.8 in Lean and MetS, respectively, P < 0.001). BSI in the left anterior descending coronary artery was augmented in pigs with MetS. Structural changes were associated with capillary rarefaction, decreased hyperemic-to-basal coronary flow velocity ratio, and augmented myogenic tone. MetS CRMs showed a reduced collagen-to-elastin ratio, while immunostaining for the receptor for advanced glycation end products was selectively increased in the left anterior descending coronary artery. These data suggest that MetS causes hypertrophic inward remodeling of CRMs and capillary rarefaction, which contribute to decreased coronary flow and myocardial ischemia. Moreover, our data demonstrate novel differential remodeling between coronary micro- and macrovessels in a clinically relevant model of MetS.

TMEM16A channels generate Ca²⁺-activated Cl⁻ currents in cerebral artery smooth muscle cells

Transmembrane protein (TMEM)16A channels are recently discovered membrane proteins that display electrophysiological properties similar to classic Ca(2+)-activated Cl(-) (Cl(Ca)) channels in native cells. The molecular identity of proteins that generate Cl(Ca) currents in smooth muscle cells (SMCs) of resistance-size arteries is unclear. Similarly, whether cerebral artery SMCs generate Cl(Ca) currents is controversial. Here, using molecular biology and patch-clamp electrophysiology, we examined TMEM16A channel expression and characterized Cl(-) currents in arterial SMCs of resistance-size rat cerebral arteries. RT-PCR amplified transcripts for TMEM16A but not TMEM16B-TMEM16H, TMEM16J, or TMEM16K family members in isolated pure cerebral artery SMCs. Western blot analysis using an antibody that recognized recombinant (r)TMEM16A channels detected TMEM16A protein in cerebral artery lysates. Arterial surface biotinylation and immunofluorescence indicated that TMEM16A channels are located primarily within the arterial SMC plasma membrane. Whole cell Cl(Ca) currents in arterial SMCs displayed properties similar to those generated by rTMEM16A channels, including Ca(2+) dependence, current-voltage relationship linearization by an elevation in intracellular Ca(2+) concentration, a Nerstian shift in reversal potential induced by reducing the extracellular Cl(-) concentration, and a negative reversal potential shift when substituting extracellular I(-) for Cl(-). A pore-targeting TMEM16A antibody similarly inhibited both arterial SMC Cl(Ca) and rTMEM16A currents. TMEM16A knockdown using small interfering RNA also inhibited arterial SMC Cl(Ca) currents. In summary, these data indicate that TMEM16A channels are expressed, insert into the plasma membrane, and generate Cl(Ca) currents in cerebral artery SMCs.

Ca(V)1.2 channel N-terminal splice variants modulate functional surface expression in resistance size artery smooth muscle cells

Voltage-dependent Ca(2+) (Ca(V)1.2) channels are the primary Ca(2+) influx pathway in arterial smooth muscle cells and are essential for contractility regulation by a variety of stimuli, including intravascular pressure. Arterial smooth muscle cell Ca(V)1.2 mRNA is alternatively spliced at exon 1 (e1), generating e1b or e1c variants, with e1c exhibiting relatively smooth muscle-specific expression in the cardiovascular system. Here, we examined physiological functions of Ca(V)1.2e1 variants and tested the hypothesis that targeting Ca(V)1.2e1 modulates resistance size cerebral artery contractility. Custom antibodies that selectively recognize Ca(V)1.2 channel proteins containing sequences encoded by either e1b (Ca(V)1.2e1b) or e1c (Ca(V)1.2e1c) both detected Ca(V)1.2 in rat and human cerebral arteries. shRNA targeting e1b or e1c reduced expression of that Ca(V)1.2 variant, induced compensatory up-regulation of the other variant, decreased total Ca(V)1.2, and reduced intravascular pressure- and depolarization-induced vasoconstriction. Ca(V)1.2e1b and Ca(V)1.2e1c knockdown reduced whole cell Ca(V)1.2 currents, with Ca(V)1.2e1c knockdown most effectively reducing total Ca(V)1.2 and inducing the largest vasodilation. Knockdown of α(2)δ-1, a Ca(V)1.2 auxiliary subunit, reduced surface expression of both Ca(V)1.2e1 variants, inhibiting Ca(V)1.2e1c more than Ca(V)1.2e1b. e1b or e1c overexpression reduced Ca(V)1.2 surface expression and whole cell currents, leading to vasodilation, with e1c overexpression inducing the largest effect. In summary, data indicate that arterial smooth muscle cells express Ca(V)1.2 channels containing e1b or e1c-encoded N termini that contribute to Ca(V)1.2 surface expression, α(2)δ-1 preferentially traffics the Ca(V)1.2e1c variant to the plasma membrane, and targeting of Ca(V)1.2e1 message or the Ca(V)1.2 channel proximal N terminus induces vasodilation.

Adenosine receptor regulation of coronary blood flow in Ossabaw miniature swine

Adenosine clearly regulates coronary blood flow (CBF); however, contributions of specific adenosine receptor (AR) subtypes (A(1), A(2A), A(2B), A(3)) to CBF in swine have not been determined. ARs generally decrease (A(1), A(3)) or increase (A(2A), A(2B)) cyclic adenosine monophosphate, a major mediator of vasodilation. We hypothesized that A(1) antagonism potentiates coronary vasodilation and coronary stent deployment in dyslipidemic Ossabaw swine elicits impaired vasodilation to adenosine that is associated with increased A(1)/A(2A) expression. The left main coronary artery was accessed with a guiding catheter allowing intracoronary infusions. After placement of a flow wire into the left circumflex coronary artery the responses to bolus infusions of adenosine were obtained. Steady-state infusion of AR-specific agents was achieved by using a small catheter fed over the flow wire in control pigs. CBF was increased by the A(2)-nonselective agonist 2-phenylaminoadenosine (CV1808) in a dose-dependent manner. Baseline CBF was increased by the highly A(1)-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), but not changed by other AR-specific agents. The nonselective A(2) antagonist 3,7-dimethyl-1-propargylxanthine and A(2A)-selective antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM241385) abolished adenosine-induced CBF, whereas A(2B) and A(3) antagonism had no effect. Dyslipidemia and stenting decreased adenosine-induced CBF ∼70%, whereas A(1), A(2A), and A(2B) mRNA were up-regulated in dyslipidemic versus control >5-fold and there was no change in the ratio of A(1)/A(2A) protein in microvessels distal to the stent. In control Ossabaw swine A(1) antagonism by DPCPX positively regulated basal CBF. Impaired adenosine-induced CBF after stenting in dyslipidemia is most likely caused by the altered balance between A(1) and A(2A) signaling, not receptor expression.

Type 1 IP3 receptors activate BKCa channels via local molecular coupling in arterial smooth muscle cells

Plasma membrane large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels and sarcoplasmic reticulum inositol 1,4,5-trisphosphate (IP₃) receptors (IP₃Rs) are expressed in a wide variety of cell types, including arterial smooth muscle cells. Here, we studied BK_Ca channel regulation by IP₃ and IP₃Rs in rat and mouse cerebral artery smooth muscle cells. IP₃ activated BK_Ca channels both in intact cells and in excised inside-out membrane patches. IP₃ caused concentration-dependent BK_Ca channel activation with an apparent dissociation constant (K_d) of ∼4 µM at physiological voltage (−40 mV) and intracellular Ca²⁺ concentration ([Ca²⁺]_i; 10 µM). IP₃ also caused a leftward-shift in BK_Ca channel apparent Ca²⁺ sensitivity and reduced the K_d for free [Ca²⁺]_i from ∼20 to 12 µM, but did not alter the slope or maximal P_o. BAPTA, a fast Ca²⁺ buffer, or an elevation in extracellular Ca²⁺ concentration did not alter IP₃-induced BK_Ca channel activation. Heparin, an IP₃R inhibitor, and a monoclonal type 1 IP₃R (IP₃R1) antibody blocked IP₃-induced BK_Ca channel activation. Adenophostin A, an IP₃R agonist, also activated BK_Ca channels. IP₃ activated BK_Ca channels in inside-out patches from wild-type (IP₃R1^+/+) mouse arterial smooth muscle cells, but had no effect on BK_Ca channels of IP₃R1-deficient (IP₃R1^−/−) mice. Immunofluorescence resonance energy transfer microscopy indicated that IP₃R1 is located in close spatial proximity to BK_Ca α subunits. The IP₃R1 monoclonal antibody coimmunoprecipitated IP₃R1 and BK_Ca channel α and β1 subunits from cerebral arteries. In summary, data indicate that IP₃R1 activation elevates BK_Ca channel apparent Ca²⁺ sensitivity through local molecular coupling in arterial smooth muscle cells.

Metabolic syndrome and coronary artery disease in Ossabaw compared with Yucatan swine

Metabolic syndrome (MetS), a compilation of associated risk factors, increases the risk of type 2 diabetes and coronary artery disease (CAD, atherosclerosis), which can progress to the point of artery occlusion. Stents are the primary interventional treatment for occlusive CAD, and patients with MetS and hyperinsulinemia have increased restenosis. Because of its thrifty genotype, the Ossabaw pig is a model of MetS. We tested the hypothesis that, when fed high-fat diet, Ossabaw swine develop more features of MetS, greater native CAD, and greater stent-induced CAD than do Yucatan swine. Animals of each breed were divided randomly into 2 groups and fed 2 different calorie-matched diets for 40 wk: control diet (C) and high-fat, high-cholesterol atherogenic diet (H). A bare metal stent was placed in the circumflex artery, and pigs were allowed to recover for 3 wk. Characteristics of MetS, macrovascular and microvascular CAD, in-stent stenosis, and Ca(2+) signaling in coronary smooth muscle cells were evaluated. MetS characteristics including, obesity, glucose intolerance, hyperinsulinemia, and elevated arterial pressure were elevated in Ossabaw swine compared to Yucatan swine. Ossabaw swine with MetS had more extensive and diffuse native CAD and in-stent stenosis and impaired coronary blood flow regulation compared with Yucatan. In-stent atherosclerotic lesions in Ossabaw coronary arteries were less fibrous and more cellular. Coronary smooth muscle cells from Ossabaw had impaired Ca(2+) efflux and intracellular sequestration versus cells from Yucatan swine. Therefore, Ossabaw swine are a superior model of MetS, subsequent CAD, and cellular Ca(2+) signaling defects, whereas Yucatan swine are leaner and relatively resistant to MetS and CAD.

Exercise training decreases store-operated Ca2+entry associated with metabolic syndrome and coronary atherosclerosis

AIMS

Stenting attenuates restenosis, but accelerated coronary artery disease (CAD) adjacent to the stent (peri-stent CAD) remains a concern in metabolic syndrome (MetS). Smooth muscle cell proliferation, a major mechanism of CAD, is mediated partly by myoplasmic Ca2+ dysregulation and store-operated Ca2+ entry (SOCE) via canonical transient receptor potential 1 (TRPC1) channels is proposed to play a key role. Exercise is known to prevent Ca2+ dysregulation in CAD. We tested the hypothesis that MetS increases SOCE and peri-stent CAD and exercise attenuates these events.

METHODS AND RESULTS

Groups (n = 9 pigs each) were (i) healthy lean Ossabaw swine fed standard chow, (ii) excess calorie atherogenic diet fed (MetS), and (iii) aerobically exercise trained starting after 50 weeks of development of MetS (XMetS). Bare metal stents were placed after 54 weeks on diets, and CAD and SOCE were assessed 4 weeks later. Coronary cells were dispersed proximal to the stent (peri-stent) and from non-stent segments, and fura-2 fluorescence was used to assess SOCE, which was verified by Ni2+ blockade and insensitivity to nifedipine. XMetS pigs had increased physical work capacity and decreased LDL/HDL (P < 0.05), but no attenuation of robust insulin resistance, glucose intolerance, hypertriglyceridaemia, or hypertension. CAD was greater in peri-stented vs. non-stented artery segments. MetS had the greatest CAD, SOCE, and TRPC1 and STIM1 mRNA and protein expression, which were all attenuated in XMetS.

CONCLUSION

This is the first report of the protective effect of exercise on native CAD, peri-stent CAD, SOCE, and molecular expression of TRPC1, STIM1, and Orai1 in MetS.

Metabolic syndrome reduces the contribution of K+ channels to ischemic coronary vasodilation

This investigation tested the hypothesis that metabolic syndrome decreases the relative contribution of specific K(+) channels to coronary reactive hyperemia. Ca(2+)-activated (BK(Ca)), voltage-activated (K(V)), and ATP-dependent (K(ATP)) K(+) channels were investigated. Studies were conducted in anesthetized miniature Ossabaw swine fed a normal maintenance diet (11% kcal from fat) or an excess calorie atherogenic diet (43% kcal from fat, 2% cholesterol, 20% kcal from fructose) for 20 wk. The latter diet induces metabolic syndrome, increasing body weight, fasting glucose, total cholesterol, and triglyceride levels. Ischemic vasodilation was determined by the coronary flow response to a 15-s occlusion before and after cumulative administration of antagonists for BK(Ca) (penitrem A; 10 microg/kg iv), K(V) (4-aminopyridine; 0.3 mg/kg iv) and K(ATP) (glibenclamide; 1 mg/kg iv) channels. Coronary reactive hyperemia was diminished by metabolic syndrome as the repayment of flow debt was reduced approximately 30% compared with lean swine. Inhibition of BK(Ca) channels had no effect on reactive hyperemia in either lean or metabolic syndrome swine. Subsequent inhibition of K(V) channels significantly reduced the repayment of flow debt ( approximately 25%) in both lean and metabolic syndrome swine. Additional blockade of K(ATP) channels further diminished ( approximately 45%) the repayment of flow debt in lean but not metabolic syndrome swine. These data indicate that the metabolic syndrome impairs coronary vasodilation in response to cardiac ischemia via reductions in the contribution of K(+) channels to reactive hyperemia.

Contribution of BK(Ca) channels to local metabolic coronary vasodilation: Effects of metabolic syndrome

This investigation was designed to examine the hypothesis that impaired function of coronary microvascular large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels in metabolic syndrome (MetS) significantly attenuates the balance between myocardial oxygen delivery and metabolism at rest and during exercise-induced increases in myocardial oxygen consumption (MVo(2)). Studies were conducted in conscious, chronically instrumented Ossabaw swine fed a normal maintenance diet (11% kcal from fat) or an excess calorie atherogenic diet (43% kcal from fat, 2% cholesterol, 20% kcal from fructose) that induces many common features of MetS. Data were collected under baseline/resting conditions and during graded treadmill exercise before and after selective blockade of BK(Ca) channels with penitrem A (10 microg/kg iv). We found that the exercise-induced increases in blood pressure were significantly elevated in MetS swine. No differences in baseline cardiac function or heart rate were noted. Induction of MetS produced a parallel downward shift in the relationship between coronary venous Po(2) and MVo(2) (P < 0.001) that was accompanied by a marked release of lactate (negative lactate uptake) as MVo(2) was increased with exercise (P < 0.005). Inhibition of BK(Ca) channels with penitrem A did not significantly affect blood pressure, heart rate, or the relationship between coronary venous Po(2) and MVo(2) in lean or MetS swine. These data indicate that BK(Ca) channels are not required for local metabolic control of coronary blood flow under physiological (lean) or pathophysiological (MetS) conditions. Therefore, diminished function of BK(Ca) channels does not contribute to the impairment of myocardial oxygen-supply demand balance in MetS.

Impaired function of coronary BK(Ca) channels in metabolic syndrome

The role of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels in regulation of coronary microvascular function is widely appreciated, but molecular and functional changes underlying the deleterious influence of metabolic syndrome (MetS) have not been determined. Male Ossabaw miniature swine consumed for 3-6 mo a normal diet (11% kcal from fat) or an excess-calorie atherogenic diet that induces MetS (45% kcal from fat, 2% cholesterol, 20% kcal from fructose). MetS significantly impaired coronary vasodilation to the BK(Ca) opener NS-1619 in vivo (30-100 microg) and reduced the contribution of these channels to adenosine-induced microvascular vasodilation in vitro (1-100 microM). MetS reduced whole cell penitrem A (1 microM)-sensitive K(+) current and NS-1619-activated (10 microM) current in isolated coronary vascular smooth muscle cells. MetS increased the concentration of free intracellular Ca(2+) and augmented coronary vasoconstriction to the L-type Ca(2+) channel agonist BAY K 8644 (10 pM-10 nM). BK(Ca) channel alpha and beta(1) protein expression was increased in coronary arteries from MetS swine. Coronary vascular dysfunction in MetS is related to impaired BK(Ca) channel function and is accompanied by significant increases in L-type Ca(2+) channel-mediated coronary vasoconstriction.

Impaired capsaicin-induced relaxation of coronary arteries in a porcine model of the metabolic syndrome

Recent studies implicate channels of the transient receptor potential vanilloid family (e.g., TRPV1) in regulating vascular tone; however, little is known about these channels in the coronary circulation. Furthermore, it is unclear whether metabolic syndrome alters the function and/or expression of TRPV1. We tested the hypothesis that TRPV1 mediates coronary vasodilation through endothelium-dependent mechanisms that are impaired by the metabolic syndrome. Studies were conducted on coronary arteries from lean and obese male Ossabaw miniature swine. In lean pigs, capsaicin, a TRPV1 agonist, relaxed arteries in a dose-dependent manner (EC50 = 116 +/- 41 nM). Capsaicin-induced relaxation was blocked by the TRPV1 antagonist capsazepine, endothelial denudation, inhibition of nitric oxide synthase, and K+ channel antagonists. Capsaicin-induced relaxation was impaired in rings from pigs with metabolic syndrome (91 +/- 4% vs. 51 +/- 10% relaxation at 100 microM). TRPV1 immunoreactivity was prominent in coronary endothelial cells. TRPV1 protein expression was decreased 40 +/- 11% in obese pigs. Capsaicin (100 microM) elicited divalent cation influx that was abolished in endothelial cells from obese pigs. These data indicate that TRPV1 channels are functionally expressed in the coronary circulation and mediate endothelium-dependent vasodilation through a mechanism involving nitric oxide and K+ channels. Impaired capsaicin-induced vasodilation in the metabolic syndrome is associated with decreased expression of TRPV1 and cation influx.

Three novel missense mutations within the LHX4 gene are associated with variable pituitary hormone deficiencies

CONTEXT

The LHX4 LIM-homeodomain transcription factor has essential roles in pituitary gland and nervous system development. Heterozygous mutations in LHX4 are associated with combined pituitary hormone deficiency.

OBJECTIVES

Our objectives were to determine the nature and frequency of LHX4 mutations in patients with pituitary hormone deficiency and to examine the functional outcomes of observed mutations.

DESIGN

The LHX4 gene sequence was determined from patient DNA. The biochemical and gene regulatory properties of aberrant LHX4 proteins were characterized using structural predictions, pituitary gene transcription assays, and DNA binding experiments.

PATIENTS

A total of 253 patients from 245 pedigrees with GH deficiency and deficiency of at least one additional pituitary hormone was included in the study.

RESULTS

In five patients, three types of heterozygous missense mutations in LHX4 that result in substitution of conserved amino acids were identified. One substitution is between the LIM domains (R84C); the others are in the homeodomain (L190R; A210P). The patients have GH deficiency; some also display reductions in TSH, LH, FSH, or ACTH, and aberrant pituitary morphology. Structural models predict that the aberrant L190R and A210P LHX4 proteins would have impaired DNA binding and gene activation properties. Consistent with these models, EMSAs and transfection experiments using pituitary gene promoters demonstrate that whereas the R84C form has reduced activity, the L190R and A210P proteins are inactive.

CONCLUSIONS

LHX4 mutations are a relatively rare cause of combined pituitary hormone deficiency. This report extends the range of phenotypes associated with LHX4 gene mutations and describes three novel exonic mutations in the gene.