Angiogenesis: Basic Mechanisms and Clinical Applications

The development and maintenance of an adequate vascular supply is critical for the viability of normal and neoplastic tissues. Angiogenesis, the development of new blood vessels from preexisting capillary networks, plays an important role in a number of physiologic and pathologic processes, including reproduction, wound repair, inflammatory diseases, and tumor growth. Angiogenesis involves sequential steps that are triggered in response to angiogenic growth factors released by inflammatory, mesenchymal, or tumor cells that act as ligands for endothelial cell receptor tyrosine kinases. Stimulated endothelial cells detach from neighboring cells and migrate, proliferate, and form tubes. The immature tubes are subsequently invested and stabilized by pericytes or smooth muscle cells. Angiogenesis depends upon complex interactions among various classes of molecules, including adhesion molecules, proteases, structural proteins, cell surface receptors, and growth factors. The therapeutic manipulation of angiogenesis targeted against ischemic and neoplastic diseases has been investigated in preclinical animal models and in clinical trials. Proangiogenic trials that have stimulated vessel growth in ischemic coronary or peripheral tissues through expression, delivery, or stimulated release of growth factors have shown efficacy in animal models and mixed results in human clinical trials. Antiangiogenic trials have used strategies to block the function of molecules critical for new vessel growth or maturation in the treatment of a variety of malignancies, mostly with results less encouraging than those seen in preclinical models. Pro-and antiangiogenic clinical trials demonstrate that strategies for optimal drug delivery, dosing schedules, patient selection, and endpoint measurements need further investigation and refinement before the therapeutic manipulation of angiogenesis will realize its full clinical potential.

Incidence rate of pathogen-specific clinical mastitis on conventional and organic Canadian dairy farms

Mastitis is a common and costly production disease on dairy farms. In Canada, the incidence rate of clinical mastitis (IRCM) has been determined for conventionally managed dairy farms; however, no studies to date have assessed rates in organically managed systems. The objectives of this observational study were (1) to determine the producer-reported IRCM and predominant pathogen types on conventional and organic dairy farms in Southern Ontario, Canada, and (2) to evaluate the association of both mean overall IRCM and pathogen-specific IRCM with management system, housing type, and pasture access. Data from 59 dairy farms in Southern Ontario, Canada, distributed across conventional (n=41) and organic management (n=18) systems, were collected from April 2011 to May 2012. In addition to management system, farms were categorized by housing method (loose or tie-stall) and pasture access for lactating cows. Participating producers identified and collected samples from 936 cases of clinical mastitis. The most frequently isolated mastitis pathogens were coagulase-negative staphylococci, Bacillus spp., Streptococcus spp., Staphylococcus aureus, and Escherichia coli. The IRCM was higher on conventional farms than organic (23.7 vs. 13.2 cases per 100 cow-years) and was not associated with housing type (loose or tie-stall), pasture access, or herd-average milk yield. Bulk tank somatic cell count tended to be lower on conventional farms than organic (222,000 vs. 272,000 cells/mL). Pathogen-specific IRCM attributed to Staph. aureus, Bacillus spp., and E. coli was greater on conventional than organic farms, but was not associated with housing or any other factors. In conclusion, organic management was associated with reduced overall and pathogen-specific IRCM.

Regulation of L-type calcium channel by phospholemman in cardiac myocytes

We evaluated whether phospholemman (PLM) regulates L-type Ca(2+) current (ICa) in mouse ventricular myocytes. Expression of α1-subunit of L-type Ca(2+) channels between wild-type (WT) and PLM knockout (KO) hearts was similar. Compared to WT myocytes, peak ICa (at -10 mV) from KO myocytes was ~41% larger, the inactivation time constant (τ(inact)) of ICa was ~39% longer, but deactivation time constant (τ(deact)) was similar. In the presence of isoproterenol (1 μM), peak ICa was ~48% larger and τ(inact) was ~144% higher in KO myocytes. With Ba(2+) as the permeant ion, PLM enhanced voltage-dependent inactivation but had no effect on τ(deact). To dissect the molecular determinants by which PLM regulated ICa, we expressed PLM mutants by adenovirus-mediated gene transfer in cultured KO myocytes. After 24h in culture, KO myocytes expressing green fluorescent protein (GFP) had significantly larger peak ICa and longer τ(inact) than KO myocytes expressing WT PLM; thereby independently confirming the observations in freshly isolated myocytes. Compared to KO myocytes expressing GFP, KO myocytes expressing the cytoplasmic domain truncation mutant (TM43), the non-phosphorylatable S68A mutant, the phosphomimetic S68E mutant, and the signature PFXYD to alanine (ALL5) mutant all resulted in lower peak ICa. Expressing PLM mutants did not alter expression of α1-subunit of L-type Ca(2+) channels in cultured KO myocytes. Our results suggested that both the extracellular PFXYD motif and the transmembrane domain of PLM but not the cytoplasmic tail were necessary for regulation of peak ICa amplitude. We conclude that PLM limits Ca(2+) influx in cardiac myocytes by reducing maximal ICa and accelerating voltage-dependent inactivation.

Phospholemman deficiency in postinfarct hearts: enhanced contractility but increased mortality

Phospholemman (PLM) regulates [Na(+) ](i), [Ca(2+)](i) and contractility through its interactions with Na(+)-K(+)-ATPase (NKA) and Na(+) /Ca(2+) exchanger (NCX1) in the heart. Both expression and phosphorylation of PLM are altered after myocardial infarction (MI) and heart failure. We tested the hypothesis that absence of PLM regulation of NKA and NCX1 in PLM-knockout (KO) mice is detrimental. Three weeks after MI, wild-type (WT) and PLM-KO hearts were similarly hypertrophied. PLM expression was lower but fractional phosphorylation was higher in WT-MI compared to WT-sham hearts. Left ventricular ejection fraction was severely depressed in WT-MI but significantly less depressed in PLM-KO-MI hearts despite similar infarct sizes. Compared with WT-sham myocytes, the abnormal [Ca(2+) ], transient and contraction amplitudes observed in WT-MI myocytes were ameliorated by genetic absence of PLM. In addition, NCX1 current was depressed in WT-MI but not in PLM-KO-MI myocytes. Despite improved myocardial and myocyte performance, PLM-KO mice demonstrated reduced survival after MI. Our findings indicate that alterations in PLM expression and phosphorylation are important adaptations post-MI, and that complete absence of PLM regulation of NKA and NCX1 is detrimental in post-MI animals.

Regulation of in vivo cardiac contractility by phospholemman: role of Na+/Ca2+ exchange

Phospholemman (PLM), when phosphorylated at serine 68, relieves its inhibition on Na(+)-K(+)-ATPase but inhibits Na(+)/Ca(2+) exchanger 1 (NCX1) in cardiac myocytes. Under stress when catecholamine levels are high, enhanced Na(+)-K(+)-ATPase activity by phosphorylated PLM attenuates intracellular Na(+) concentration ([Na(+)](i)) overload. To evaluate the effects of PLM on NCX1 on in vivo cardiac contractility, we injected recombinant adeno-associated virus (serotype 9) expressing either the phosphomimetic PLM S68E mutant or green fluorescent protein (GFP) directly into left ventricles (LVs) of PLM-knockout (KO) mice. Five weeks after virus injection, ∼40% of isolated LV myocytes exhibited GFP fluorescence. Expression of S68E mutant was confirmed with PLM antibody. There were no differences in protein levels of α(1)- and α(2)-subunits of Na(+)-K(+)-ATPase, NCX1, and sarco(endo)plasmic reticulum Ca(2+)-ATPase between KO-GFP and KO-S68E LV homogenates. Compared with KO-GFP myocytes, Na(+)/Ca(2+) exchange current was suppressed, but resting [Na(+)](i), Na(+)-K(+)-ATPase current, and action potential amplitudes were similar in KO-S68E myocytes. Resting membrane potential was slightly lower and action potential duration at 90% repolarization (APD(90)) was shortened in KO-S68E myocytes. Isoproterenol (Iso; 1 μM) increased APD(90) in both groups of myocytes. After Iso, [Na(+)](i) increased monotonically in paced (2 Hz) KO-GFP but reached a plateau in KO-S68E myocytes. Both systolic and diastolic [Ca(2+)](i) were higher in Iso-stimulated KO-S68E myocytes paced at 2 Hz. Echocardiography demonstrated similar resting heart rate, ejection fraction, and LV mass between KO-GFP and KO-S68E mice. In vivo closed-chest catheterization demonstrated enhanced contractility in KO-S68E compared with KO-GFP hearts stimulated with Iso. We conclude that under catecholamine stress when [Na(+)](i) is high, PLM minimizes [Na(+)](i) overload by relieving its inhibition of Na(+)-K(+)-ATPase and preserves inotropy by simultaneously inhibiting Na(+)/Ca(2+) exchanger.

Health Heritage© a web-based tool for the collection and assessment of family health history: initial user experience and analytic validity

A detailed family health history is currently the most potentially useful tool for diagnosis and risk assessment in clinical genetics. We developed and evaluated the usability and analytic validity of a patient-driven web-based family health history collection and analysis tool. Health Heritage(©) guides users through the collection of their family health history by relative, generates a pedigree, completes risk assessment, stratification, and recommendations for 89 conditions. We compared the performance of Health Heritage to that of Usual Care using a nonrandomized cohort trial of 109 volunteers. We contrasted the completeness and sensitivity of family health history collection and risk assessments derived from Health Heritage and Usual Care to those obtained by genetic counselors and genetic assessment teams. Nearly half (42%) of the Health Heritage participants reported discovery of health risks; 63% found the information easy to understand and 56% indicated it would change their health behavior. Health Heritage consistently outperformed Usual Care in the completeness and accuracy of family health history collection, identifying 60% of the elevated risk conditions specified by the genetic team versus 24% identified by Usual Care. Health Heritage also had greater sensitivity than Usual Care when comparing the identification of risks. These results suggest a strong role for automated family health history collection and risk assessment and underscore the potential of these data to serve as the foundation for comprehensive, cost-effective personalized genomic medicine.

Metabolic indicators of nutritional stress are not predictive of abnormal oral behavior in piglets

Belly nosing is an abnormal oral-nasal behavior that can develop to high levels in newly weaned piglets and may signal nutritional need. The effects of feed restriction on both behavior and metabolic serum parameters were examined in 128 weaned piglets. All pigs were fed ad libitum during week 1, and during week 2, half of all pens (N=8) were restricted to 65% of ad libitum intake. Blood samples were collected on days 3 and 10 after weaning and behavior was observed from video recordings on days 5 and 12. Piglets were classified as early 'nosers' or early 'non-nosers' based on their behavior on day 5. Feed restriction resulted in elevated non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB) and both lower glucose and a NEFA/glucose ratio, but belly nosing was not affected. Piglets classified as 'nosers' did not have blood profiles indicating they were in greater nutritional need compared to 'non-nosers' in the first week of weaning, nor did they increase belly nosing or other piglet directed behaviors when restricted in week 2. Overall, no associations were found between blood parameters indicative of nutritional stress and belly nosing. This study identifies serum glucose, BHB and NEFA as well as the glucose/NEFA ratio as useful indicators of nutritional stress in newly weaned piglets.

Phospholemman and beta-adrenergic stimulation in the heart

Phosphorylation at serine 68 of phospholemman (PLM) in response to beta-adrenergic stimulation results in simultaneous inhibition of cardiac Na(+)/Ca(2+) exchanger NCX1 and relief of inhibition of Na(+)-K(+)-ATPase. The role of PLM in mediating beta-adrenergic effects on in vivo cardiac function was investigated with congenic PLM-knockout (KO) mice. Echocardiography showed similar ejection fraction between wild-type (WT) and PLM-KO hearts. Cardiac catheterization demonstrated higher baseline contractility (+dP/dt) but similar relaxation (-dP/dt) in PLM-KO mice. In response to isoproterenol (Iso), maximal +dP/dt was similar but maximal -dP/dt was reduced in PLM-KO mice. Dose-response curves to Iso (0.5-25 ng) for WT and PLM-KO hearts were superimposable. Maximal +dP/dt was reached 1-2 min after Iso addition and declined with time in WT but not PLM-KO hearts. In isolated myocytes paced at 2 Hz. contraction and intracellular Ca(2+) concentration ([Ca(2+)](i)) transient amplitudes and [Na(+)](i) reached maximum 2-4 min after Iso addition, followed by decline in WT but not PLM-KO myocytes. Reducing pacing frequency to 0.5 Hz resulted in much smaller increases in [Na(+)](i) and no decline in contraction and [Ca(2+)](i) transient amplitudes with time in Iso-stimulated WT and PLM-KO myocytes. Although baseline Na(+)-K(+)-ATPase current was 41% higher in PLM-KO myocytes because of increased alpha(1)- but not alpha(2)-subunit activity, resting [Na(+)](i) was similar between quiescent WT and PLM-KO myocytes. Iso increased alpha(1)-subunit current (I(alpha1)) by 73% in WT but had no effect in PLM-KO myocytes. Iso did not affect alpha(2)-subunit current (I(alpha2)) in WT and PLM-KO myocytes. In both WT and NCX1-KO hearts, PLM coimmunoprecipitated with Na(+)-K(+)-ATPase alpha(1)- and alpha(2)-subunits, indicating that association of PLM with Na(+)-K(+)-ATPase did not require NCX1. We conclude that under stressful conditions in which [Na(+)](i) was high, beta-adrenergic agonist-mediated phosphorylation of PLM resulted in time-dependent reduction in inotropy due to relief of inhibition of Na(+)-K(+)-ATPase.

Extracellular potassium dependence of the Na+-K+-ATPase in cardiac myocytes: isoform specificity and effect of phospholemman

Cardiac Na(+)-K(+)-ATPase (NKA) regulates intracellular Na(+), which in turn affects intracellular Ca(2+) and contractility via the Na(+)/Ca(2+) exchanger. Extracellular K(+) concentration ([K(+)]) is a central regulator of NKA activity. Phospholemman (PLM) has recently been recognized as a critical regulator of NKA in the heart. PLM reduces the intracellular Na(+) affinity of NKA, an effect relieved by PLM phosphorylation. Here we tested whether the NKA alpha(1)- vs. alpha(2)- isoforms have different external K(+) sensitivity and whether PLM and PKA activation affects the NKA affinity for K(+) in mouse cardiac myocytes. We measured the external [K(+)] dependence of the pump current generated by the ouabain-resistant NKA isoform in myocytes from wild-type (WT) mice (i.e., current due to NKA-alpha(1)) and mice in which the NKA isoforms have swapped ouabain affinities (alpha(1) is ouabain sensitive and alpha(2) is ouabain resistant) to assess current due to NKA-alpha(2). We found that NKA-alpha(1) has a higher affinity for external K(+) than NKA-alpha(2) [half-maximal pump activation (K(0.5)) = 1.5 +/- 0.1 vs. 2.9 +/- 0.3 mM]. The apparent external K(+) affinity of NKA was significantly lower in myocytes from WT vs. PLM-knockout mice (K(0.5) = 2.0 +/- 0.2 vs. 1.05 +/- 0.08 mM). However, PKA activation by isoproterenol (1 microM) did not alter the K(0.5) of NKA for external K(+) in WT myocytes. We conclude that 1) NKA-alpha(1) has higher affinity for K(+) than NKA-alpha(2) in cardiac myocytes, 2) PLM decreases the apparent external K(+) affinity of NKA, and 3) phosphorylation of PLM at the cytosolic domain does not alter apparent extracellular K(+) affinity of NKA.

Regulation of cardiac myocyte contractility by phospholemman: Na+/Ca2+ exchange versus Na+ -K+ -ATPase

Phospholemman (PLM) regulates cardiac Na(+)/Ca(2+) exchanger (NCX1) and Na(+)-K(+)-ATPase in cardiac myocytes. PLM, when phosphorylated at Ser(68), disinhibits Na(+)-K(+)-ATPase but inhibits NCX1. PLM regulates cardiac contractility by modulating Na(+)-K(+)-ATPase and/or NCX1. In this study, we first demonstrated that adult mouse cardiac myocytes cultured for 48 h had normal surface membrane areas, t-tubules, and NCX1 and sarco(endo)plasmic reticulum Ca(2+)-ATPase levels, and retained near normal contractility, but alpha(1)-subunit of Na(+)-K(+)-ATPase was slightly decreased. Differences in contractility between myocytes isolated from wild-type (WT) and PLM knockout (KO) hearts were preserved after 48 h of culture. Infection with adenovirus expressing green fluorescent protein (GFP) did not affect contractility at 48 h. When WT PLM was overexpressed in PLM KO myocytes, contractility and cytosolic Ca(2+) concentration ([Ca(2+)](i)) transients reverted back to those observed in cultured WT myocytes. Both Na(+)-K(+)-ATPase current (I(pump)) and Na(+)/Ca(2+) exchange current (I(NaCa)) in PLM KO myocytes rescued with WT PLM were depressed compared with PLM KO myocytes. Overexpressing the PLMS68E mutant (phosphomimetic) in PLM KO myocytes resulted in the suppression of I(NaCa) but had no effect on I(pump). Contractility, [Ca(2+)](i) transient amplitudes, and sarcoplasmic reticulum Ca(2+) contents in PLM KO myocytes overexpressing the PLMS68E mutant were depressed compared with PLM KO myocytes overexpressing GFP. Overexpressing the PLMS68A mutant (mimicking unphosphorylated PLM) in PLM KO myocytes had no effect on I(NaCa) but decreased I(pump). Contractility, [Ca(2+)](i) transient amplitudes, and sarcoplasmic reticulum Ca(2+) contents in PLM KO myocytes overexpressing the S68A mutant were similar to PLM KO myocytes overexpressing GFP. We conclude that at the single-myocyte level, PLM affects cardiac contractility and [Ca(2+)](i) homeostasis primarily by its direct inhibitory effects on Na(+)/Ca(2+) exchange.

Lysophosphatidic acid (LPA) and angiogenesis

Lysophosphatidic acid (LPA) is a simple lipid with many important biological functions such as the regulation of cellular proliferation, cellular migration, differentiation, and suppression of apoptosis. Although a direct angiogenic effect of LPA has not been reported to date, there are indications that LPA promotes angiogenesis. In addition, LPA is a chemoattractant for cultured endothelial cells and promotes barrier function in such cultures. To test the hypothesis that LPA is angiogenic, we used the chicken chorio-allantoic membrane (CAM) assay. Sequence analysis of the cloned, full-length chicken LPA receptor cDNAs revealed three receptor types that are orthologous to the mammalian LPA(1), LPA(2), and LPA(3) receptors. We document herein that LPA is angiogenic in the CAM system and further that synthetic LPA receptor agonists and antagonists mimic or block this response, respectively. Our results predict that LPA receptor antagonists are a possible therapeutic route to interdicting angiogenesis.

Phospholemman-mediated activation of Na/K-ATPase limits [Na]i and inotropic state during beta-adrenergic stimulation in mouse ventricular myocytes

BACKGROUND

Cardiac Na/K-ATPase (NKA) regulates intracellular Na ([Na](i)), which in turn affects intracellular Ca and thus contractility via Na/Ca exchange. Recent evidence shows that phosphorylation of the NKA-associated small transmembrane protein phospholemman (PLM) mediates beta-adrenergic-induced NKA stimulation.

METHODS AND RESULTS

Here, we tested whether PLM phosphorylation during beta-adrenergic activation limits the rise in [Na](i), Ca transient amplitude, and triggered arrhythmias in mouse ventricular myocytes. In myocytes from wild-type (WT) mice, [Na](i) increased on field stimulation at 2 Hz from 11.1+/-1.8 mmol/L to a plateau of 15.2+/-1.5 mmol/L. Isoproterenol induced a decrease in [Na](i) to 12.0+/-1.2 mmol/L. In PLM knockout (PLM-KO) mice in which beta-adrenergic stimulation does not activate NKA, [Na](i) also increased at 2 Hz (from 10.4+/-1.2 to 17.0+/-1.5 mmol/L) but was unaltered by isoproterenol. The PLM-mediated decrease in [Na](i) in WT mice could limit the isoproterenol-induced inotropic state. Indeed, the isoproterenol-induced increase in the amplitude of Ca transients was significantly smaller in the WT mice (5.2+/-0.4- versus 7.1+/-0.5-fold in PLM-KO mice). This also was the case for the sarcoplasmic reticulum Ca content, which increased by 1.27+/-0.09-fold in WT mice versus 1.53+/-0.09-fold in PLM-KO mice. The higher sarcoplasmic reticulum Ca content in PLM-KO versus WT mice was associated with an increased propensity for spontaneous Ca transients and contractions in PLM-KO mice.

CONCLUSIONS

These data suggest that PLM phosphorylation and NKA stimulation are an integral part of the sympathetic fight-or-flight response, tempering the rise in [Na](i) and cellular Ca loading and perhaps limiting Ca overload-induced arrhythmias.

RNA toxicity in myotonic muscular dystrophy induces NKX2-5 expression

Myotonic muscular dystrophy (DM1) is the most common inherited neuromuscular disorder in adults and is considered the first example of a disease caused by RNA toxicity. Using a reversible transgenic mouse model of RNA toxicity in DM1, we provide evidence that DM1 is associated with induced NKX2-5 expression. Transgene expression resulted in cardiac conduction defects, increased expression of the cardiac-specific transcription factor NKX2-5 and profound disturbances in connexin 40 and connexin 43. Notably, overexpression of the DMPK 3' UTR mRNA in mouse skeletal muscle also induced transcriptional activation of Nkx2-5 and its targets. In human muscles, these changes were specific to DM1 and were not present in other muscular dystrophies. The effects on NKX2-5 and its downstream targets were reversed by silencing toxic RNA expression. Furthermore, using Nkx2-5+/- mice, we show that NKX2-5 is the first genetic modifier of DM1-associated RNA toxicity in the heart.

Characterization of the phospholemman knockout mouse heart: depressed left ventricular function with increased Na-K-ATPase activity

Phospholemman (PLM, FXYD1), abundantly expressed in the heart, is the primary cardiac sarcolemmal substrate for PKA and PKC. Evidence supports the hypothesis that PLM is part of the cardiac Na-K pump complex and provides the link between kinase activity and pump modulation. PLM has also been proposed to modulate Na/Ca exchanger activity and may be involved in cell volume regulation. This study characterized the phenotype of the PLM knockout (KO) mouse heart to further our understanding of PLM function in the heart. PLM KO mice were bred on a congenic C57/BL6 background. In vivo conductance catheter measurements exhibited a mildly depressed cardiac contractile function in PLM KO mice, which was exacerbated when hearts were isolated and Langendorff perfused. There were no significant differences in action potential morphology in paced Langendorff-perfused hearts. Depressed contractile function was associated with a mild cardiac hypertrophy in PLM KO mice. Biochemical analysis of crude ventricular homogenates showed a significant increase in Na-K-ATPase activity in PLM KO hearts compared with wild-type controls. SDS-PAGE and Western blot analysis of ventricular homogenates revealed small, nonsignificant changes in Na- K-ATPase subunit expression, with two-dimensional gel (isoelectric focusing, SDS-PAGE) analysis revealing minimal changes in ventricular protein expression, indicating that deletion of PLM was the primary reason for the observed PLM KO phenotype. These studies demonstrate that PLM plays an important role in the contractile function of the normoxic mouse heart. Data are consistent with the hypothesis that PLM modulates Na-K-ATPase activity, indirectly affecting intracellular Ca and hence contractile function.

Phospholemman does not participate in forskolin-induced swine carotid artery relaxation

Phosphorylation of phospholemman (PLM) on ser68 has been proposed to at least partially mediate cyclic AMP (cAMP) mediated relaxation of arterial smooth muscle. We evaluated the time course of the phosphorylation of phospholemman (PLM) on ser68, myosin regulatory light chains (MRLC) on ser19, and heat shock protein 20 (HSP20) on ser16 during a transient forskolin-induced relaxation of histamine-stimulated swine carotid artery. We also evaluated the dose response for forskolin- and nitroglycerin-induced relaxation in phenylephrine-stimulated PLM-/- and PLM+/+ mice. The time course for changes in ser19 MRLC dephosphorylation and ser16 HSP20 phosphorylation was appropriate to explain the forskolin-induced relaxation and the recontraction observed upon washout of forskolin. However, the time course for changes in ser68 PLM phosphorylation was too slow to explain forskolin-induced changes in force. There was no difference in the phenylephrine contractile dose response or in forskolin-induced relaxation dose response observed in PLM-/- and PLM+/+ aortae. In aortae precontracted with phenylephrine, nitroglycerin induced a slightly, but significantly greater relaxation in PLM-/- compared to PLM+/+ aortae. These data are consistent with the hypothesis that ser19 MRLC dephosphorylation and ser16 HSP20 phosphorylation are involved in forskolin-induced relaxation. Our data suggest that PLM phosphorylation is not significantly involved in forskolin-induced arterial relaxation.

A1 adenosine receptor activation promotes angiogenesis and release of VEGF from monocytes

Adenosine is a proangiogenic purine nucleoside released from ischemic and hypoxic tissues. Of the 4 adenosine receptor (AR) subtypes (A1, A2A, A2B, and A3), the A2 and A3 have been previously linked to the modulation of angiogenesis. We used the chicken chorioallantoic membrane (CAM) model to determine whether A1 AR activation affects angiogenesis. We cloned and pharmacologically characterized chicken AR subtypes to evaluate the selectivity of various agonists and antagonists. Application of the A1 AR-selective agonist N6-cyclopentyladenosine (CPA; 100 nmol/L) to the CAM resulted in a 40% increase in blood vessel number (P<0.01), which was blocked by the A1 AR-selective antagonist C8-(N-methylisopropyl)-amino-N6-(5'-endohydroxy)-endonorbornan-2-yl-9-methyladenine (WRC-0571; 1 micromol/L). Selective A2A AR agonists did not stimulate angiogenesis in the CAM. In an ex vivo rat aortic ring model of angiogenesis that includes cocultured endothelial cells, fibroblasts, and smooth muscle cells, 50 nmol/L CPA did not directly stimulate capillary formation; however, medium from human mononuclear cells pretreated with CPA, but not vehicle, increased capillary formation by 48% (P<0.05). This effect was blocked by WRC-0571 (1.5 micromol/L) or anti-VEGF antibody (1 microg/mL). CPA (5 nmol/L) stimulated a 1.7-fold increase in VEGF release from the mononuclear cells. This is the first study to show that A1 AR activation induces angiogenesis. Stimulation of A2 ARs on endothelial cells results in proliferation and tube formation, and A2 and A3 ARs on inflammatory cells modulate release of angiogenic factors. We conclude that adenosine promotes a coordinated angiogenic response through its interactions with multiple receptors on multiple cell types.

Regulation of cardiac Na+/Ca2+ exchanger by phospholemman

Phospholemman (PLM) is the first sequenced member of the FXYD family of regulators of ion transport. The mature protein has 72 amino acids and consists of an extracellular N terminus containing the signature FXYD motif, a single transmembrane (TM) domain, and a cytoplasmic C-terminal domain containing four potential sites for phosphorylation. PLM and other members of the FXYD family are known to regulate Na+-K+-ATPase. Using adenovirus-mediated gene transfer into adult rat cardiac myocytes, we showed that changes in contractility and intracellular Ca2+ homeostasis associated with PLM overexpression or downregulation are not consistent with the effects expected from inhibition of Na+-K+-ATPase by PLM. Additional studies with heterologous expression of PLM and cardiac Na+/Ca2+ exchanger 1 (NCX1) in HEK293 cells and cardiac myocytes isolated from PLM-deficient mice demonstrated by co-localization, co-immunoprecipitation, and electrophysiological and radioactive tracer uptake techniques that PLM associates with NCX1 in the sarcolemma and transverse tubules and that PLM inhibits NCX1, independent of its effects on Na+-K+-ATPase. Mutational analysis indicates that the cytoplasmic domain of PLM is required for its regulation of NCX1. In addition, experiments using phosphomimetic and phospho-deficient PLM mutants, as well as activators of protein kinases A and C, indicate that PLM phosphorylated at serine68 is the active form that inhibits NCX1. This is in sharp contrast to the finding that the unphosphorylated PLM form inhibits Na+-K+-ATPase. We conclude that PLM regulates cardiac contractility by modulating the activities of NCX and Na+-K+-ATPase.

Phospholemman phosphorylation mediates the protein kinase C-dependent effects on Na+/K+ pump function in cardiac myocytes

Because phospholemman (PLM) regulates the Na(+)/K(+) pump (NKA) and is a major cardiac phosphorylation target for both protein kinase A (at Ser68) and protein kinase C (PKC) (at both Ser63 and Ser68), we evaluated whether PLM mediates the PKC-dependent regulation of NKA function and protein kinase A/PKC crosstalk in ventricular myocytes. PKC was activated by PDBu (300 nmol/L), and we measured NKA-mediated [Na(+)](i) decline (fluorescence measurements) and current (I(pump)) (voltage clamp). In wild-type mouse myocytes, PDBu increased PLM phosphorylation at Ser63 and Ser68, I(pump) (both at 10 and 100 mmol/L Na(+) in the pipette solution) and maximal NKA-mediated Na(+) extrusion rate (V(max)) from 7.9+/-1.1 to 12.7+/-1.9 mmol.L(-1) per minute without altering NKA affinity for internal Na(+) (K(0.5)). In PLM knockout mice, PDBu had no effect on either V(max) or K(0.5). After pretreatment with isoproterenol (ISO) (1 mumol/L), PDBu still increased the NKA V(max) and PLM phosphorylation at Ser63 and Ser68. Conversely, after pretreatment with PDBu, ISO further increased the Na(+) affinity of NKA and phosphorylation at Ser68, as it did alone without PDBu. The final NKA activity was independent of the application sequence. The NKA activity in PLM knockout myocytes, after normalizing the protein level, was similar to that after PDBu and ISO treatment. We conclude that (1) PLM mediates the PKC-dependent activation of NKA function in cardiac myocytes, (2) PDBu and ISO effects are additive in the mouse (affecting mainly V(max) and K(0.5), respectively), and (3) PDBu and ISO combine to activate NKA in wild-type to the level found in the PLM knockout mouse.

Altered contractility and [Ca2+]i homeostasis in phospholemman-deficient murine myocytes: role of Na+/Ca2+ exchange

Phospholemman (PLM) regulates contractility and Ca(2+) homeostasis in cardiac myocytes. We characterized excitation-contraction coupling in myocytes isolated from PLM-deficient mice backbred to a pure congenic C57BL/6 background. Cell length, cell width, and whole cell capacitance were not different between wild-type and PLM-null myocytes. Compared with wild-type myocytes, Western blots indicated total absence of PLM but no changes in Na(+)/Ca(2+) exchanger, sarcoplasmic reticulum (SR) Ca(2+)-ATPase, alpha(1)-subunit of Na(+)-K(+)-ATPase, and calsequestrin levels in PLM-null myocytes. At 5 mM extracellular Ca(2+) concentration ([Ca(2+)](o)), contraction and cytosolic [Ca(2+)] ([Ca(2+)](i)) transient amplitudes and SR Ca(2+) contents in PLM-null myocytes were significantly (P < 0.0004) higher than wild-type myocytes, whereas the converse was true at 0.6 mM [Ca(2+)](o). This pattern of contractile and [Ca(2+)](i) transient abnormalities in PLM-null myocytes mimics that observed in adult rat myocytes overexpressing the cardiac Na(+)/Ca(2+) exchanger. Indeed, we have previously reported that Na(+)/Ca(2+) exchange currents were higher in PLM-null myocytes. Activation of protein kinase A resulted in increased inotropy such that there were no longer any contractility differences between the stimulated wild-type and PLM-null myocytes. Protein kinase C stimulation resulted in decreased contractility in both wild-type and PLM-null myocytes. Resting membrane potential and action potential amplitudes were similar, but action potential duration was much prolonged (P < 0.04) in PLM-null myocytes. Whole cell Ca(2+) current densities were similar between wild-type and PLM-null myocytes, as were the fast- and slow-inactivation time constants. We conclude that a major function of PLM is regulation of cardiac contractility and Ca(2+) fluxes, likely by modulating Na(+)/Ca(2+) exchange activity.

Phospholemman inhibition of the cardiac Na+/Ca2+ exchanger. Role of phosphorylation

We have demonstrated previously that phospholemman (PLM), a 15-kDa integral sarcolemmal phosphoprotein, inhibits the cardiac Na+/Ca2+ exchanger (NCX1). In addition, protein kinase A phosphorylates serine 68, whereas protein kinase C phosphorylates both serine 63 and serine 68 of PLM. Using human embryonic kidney 293 cells that are devoid of both endogenous PLM and NCX1, we first demonstrated that the exogenous NCX1 current (I(NaCa)) was increased by phorbol 12-myristate 13-acetate (PMA) but not by forskolin. When co-expressed with NCX1, PLM resulted in: (i) decreases in I(NaCa), (ii) attenuation of the increase in I(NaCa) by PMA, and (iii) additional reduction in I(NaCa) in cells treated with forskolin. Mutating serine 63 to alanine (S63A) preserved the sensitivity of PLM to forskolin in terms of suppression of I(NaCa), whereas mutating serine 68 to alanine (S68A) abolished the inhibitory effect of PLM on I(NaCa). Mutating serine 68 to glutamic acid (phosphomimetic) resulted in additional suppression of I(NaCa) as compared with wild-type PLM. These results suggest that PLM phosphorylated at serine 68 inhibited I(NaCa). The physiological significance of inhibition of NCX1 by phosphorylated PLM was evaluated in PLM-knock-out (KO) mice. When compared with wild-type myocytes, I(NaCa) was significant larger in PLM-KO myocytes. In addition, the PMA-induced increase in I(NaCa) was significantly higher in PLM-KO myocytes. By contrast, forskolin had no effect on I(NaCa) in wild-type myocytes. We conclude that PLM, when phosphorylated at serine 68, inhibits Na+/Ca2+ exchange in the heart.

Phospholemman overexpression inhibits Na+-K+-ATPase in adult rat cardiac myocytes: relevance to decreased Na+ pump activity in postinfarction myocytes

Messenger RNA levels of phospholemman (PLM), a member of the FXYD family of small single-span membrane proteins with putative ion-transport regulatory properties, were increased in postmyocardial infarction (MI) rat myocytes. We tested the hypothesis that the previously observed reduction in Na+-K+-ATPase activity in MI rat myocytes was due to PLM overexpression. In rat hearts harvested 3 and 7 days post-MI, PLM protein expression was increased by two- and fourfold, respectively. To simulate increased PLM expression post-MI, PLM was overexpressed in normal adult rat myocytes by adenovirus-mediated gene transfer. PLM overexpression did not affect the relative level of phosphorylation on serine68 of PLM. Na+-K+-ATPase activity was measured as ouabain-sensitive Na+-K+ pump current (Ip). Compared with control myocytes overexpressing green fluorescent protein alone, Ip measured in myocytes overexpressing PLM was significantly (P < 0.0001) lower at similar membrane voltages, pipette Na+ ([Na+]pip) and extracellular K+ ([K+]o) concentrations. From -70 to +60 mV, neither [Na+]pip nor [K+]o required to attain half-maximal Ip was significantly different between control and PLM myocytes. This phenotype of decreased V(max) without appreciable changes in K(m) for Na+ and K+ in PLM-overexpressed myocytes was similar to that observed in MI rat myocytes. Inhibition of Ip by PLM overexpression was not due to decreased Na+-K+-ATPase expression because there were no changes in either protein or messenger RNA levels of either alpha1- or alpha2-isoforms of Na+-K+-ATPase. In native rat cardiac myocytes, PLM coimmunoprecipitated with alpha-subunits of Na+-K+-ATPase. Inhibition of Na+-K+-ATPase by PLM overexpression, in addition to previously reported decrease in Na+-K+-ATPase expression, may explain altered V(max) but not K(m) of Na+-K+-ATPase in postinfarction rat myocytes.

Phospholemman-Phosphorylation Mediates the β-Adrenergic Effects on Na/K Pump Function in Cardiac Myocytes

Cardiac sympathetic stimulation activates beta-adrenergic (beta-AR) receptors and protein kinase A (PKA) phosphorylation of proteins involved in myocyte Ca regulation. The Na/K-ATPase (NKA) is essential in regulating intracellular [Na] ([Na]i), which in turn affects [Ca]i via Na/Ca exchange. However, how PKA modifies NKA function is unknown. Phospholemman (PLM), a member of the FXYD family of proteins that interact with NKA in various tissues, is a major PKA substrate in heart. Here we tested the hypothesis that PLM phosphorylation is responsible for the PKA effects on cardiac NKA function using wild-type (WT) and PLM knockout (PLM-KO) mice. We measured NKA-mediated [Na]i decline and current (IPump) to assess beta-AR effects on NKA function in isolated myocytes. In WT myocytes, 1 micromol/L isoproterenol (ISO) increased PLM phosphorylation and stimulated NKA activity mainly by increasing its affinity for internal Na (Km decreased from 18.8+/-1.4 to 13.6+/-1.5 mmol/L), with no significant effect on the maximum pump rate. This led to a significant decrease in resting [Na]i (from 12.5+/-1.8 to 10.5+/-1.4 mmol/L). In PLM-KO mice under control conditions Km (14.2+/-1.5 mmol/L) was lower than in WT, but comparable to that for WT in the presence of ISO. Furthermore, ISO had no significant effect on NKA function in PLM-KO mice. ATPase activity in sarcolemmal vesicles also showed a lower Km(Na) in PLM-KO versus WT (12.9+/-0.9 versus 16.2+/-1.5). Thus, PLM inhibits NKA activity by decreasing its [Na]i affinity, and this inhibitory effect is relieved by PKA activation. We conclude that PLM modulates the NKA function in a manner similar to the way phospholamban affects the related SR Ca-ATPase (inhibition of transport substrate affinity, that is relieved by phosphorylation).

Identification of an endogenous inhibitor of the cardiac Na+/Ca2+ exchanger, phospholemman

Rapid and precise control of Na(+)/Ca(2+) exchanger (NCX1) activity is essential in the maintenance of beat-to-beat Ca(2+) homeostasis in cardiac myocytes. Here, we show that phospholemman (PLM), a 15-kDa integral sarcolemmal phosphoprotein, is a novel endogenous protein inhibitor of cardiac NCX1. Using a heterologous expression system that is devoid of both endogenous PLM and NCX1, we first demonstrated by confocal immunofluorescence studies that both exogenous PLM and NCX1 co-localized at the plasma membrane. Reciprocal co-immunoprecipitation studies revealed specific protein-protein interaction between PLM and NCX1. The functional consequences of direct association of PLM with NCX1 was the inhibition of NCX1 activity, as demonstrated by whole-cell patch clamp studies to measure NCX1 current density and radiotracer flux assays to assess Na(+)-dependent (45)Ca(2+) uptake. Inhibition of NCX1 by PLM was specific, because a single mutation of serine 68 to alanine in PLM resulted in a complete loss of inhibition of NCX1 current, although association of the PLM mutant with NCX1 was unaltered. In native adult cardiac myocytes, PLM co-immunoprecipitated with NCX1. We conclude that PLM, a member of the FXYD family of small ion transport regulators known to modulate Na(+)-K(+)-ATPase, also regulates Na(+)/Ca(2+) exchange in the heart.

Serine 68 of phospholemman is critical in modulation of contractility, [Ca2+]i transients, and Na+/Ca2+ exchange in adult rat cardiac myocytes

Overexpression of phospholemman (PLM) in normal adult rat cardiac myocytes altered contractile function and cytosolic Ca2+ concentration ([Ca2+]i) homeostasis and inhibited Na+/Ca2+ exchanger (NCX1). In addition, PLM coimmunoprecipitated and colocalized with NCX1 in cardiac myocyte lysates. In this study, we evaluated whether the cytoplasmic domain of PLM is crucial in mediating its effects on contractility, [Ca2+]i transients, and NCX1 activity. Canine PLM or its derived mutants were overexpressed in adult rat myocytes by adenovirus-mediated gene transfer. Confocal immunofluorescence images using canine-specific PLM antibodies demonstrated that the exogenous PLM or its mutants were correctly targeted to sarcolemma, t-tubules, and intercalated discs, with little to none detected in intracellular compartments. Overexpression of canine PLM or its mutants did not affect expression of NCX1, sarco(endo)plasmic reticulum Ca(2+)-ATPase, Na(+)-K(+)-ATPase, and calsequestrin in adult rat myocytes. A COOH-terminal deletion mutant in which all four potential phosphorylation sites (Ser62, Ser63, Ser68, and Thr69) were deleted, a partial COOH-terminal deletion mutant in which Ser68 and Thr69 were deleted, and a mutant in which all four potential phosphorylation sites were changed to alanine all lost wild-type PLM's ability to modulate cardiac myocyte contractility. These observations suggest the importance of Ser68 or Thr69 in mediating PLM's effect on cardiac contractility. Focusing on Ser68, the Ser68 to Glu mutant was fully effective, the Ser63 to Ala (leaving Ser68 intact) mutant was partially effective, and the Ser68 to Ala mutant was completely ineffective in modulating cardiac contractility, [Ca2+]i transients, and NCX1 currents. Both the Ser63 to Ala and Ser68 to Ala mutants, as well as PLM, were able to coimmunoprecipitate NCX1. It is known that Ser68 in PLM is phosphorylated by both protein kinases A and C. We conclude that regulation of cardiac contractility, [Ca2+]i transients, and NCX1 activity by PLM is critically dependent on Ser68. We suggest that PLM phosphorylation at Ser68 may be involved in cAMP- and/or protein kinase C-dependent regulation of cardiac contractility.

Hypertrophy, increased ejection fraction, and reduced Na-K-ATPase activity in phospholemman-deficient mice

Phospholemman (FXYD1), a 72-amino acid transmembrane protein abundantly expressed in the heart and skeletal muscle, is a major substrate for phosphorylation in the cardiomyocyte sarcolemma. Biochemical, cellular, and electrophysiological studies have suggested a number of possible roles for this protein, including ion channel modulator, taurine-release channel, Na(+)/Ca(2+) exchanger modulator, and Na-K-ATPase-associated subunit. We have generated a phospholemman-deficient mouse. The adult null mice exhibited increased cardiac mass, larger cardiomyocytes, and ejection fractions that were 9% higher by magnetic resonance imaging compared with wild-type animals. Notably, this occurred in the absence of hypertension. Total Na-K-ATPase activity was 50% lower in the phospholemman-deficient hearts. Expression (per unit of membrane protein) of total Na-K-ATPase was only slightly diminished, but expression of the minor alpha(2)-isoform, which has been specifically implicated in the control of contractility, was reduced by 60%. The absence of phospholemman thus results in a complex response, including a surprisingly large reduction in intrinsic Na-K-ATPase activity, changes in Na-K-ATPase isoform expression, increase in ejection fraction, and increase in cardiac mass. We hypothesize that a primary effect of phospholemman is to modulate the Na-K-ATPase and that its reduced activity initiates compensatory responses.

Effects of phospholemman expression on swelling-activated ion currents and volume regulation in embryonic kidney cells

Phospholemman (PLM) is a 72-amino-acid phosphoprotein that is a major substrate for cAMP-dependent protein kinase, protein kinase C, and NIMA kinase. In lipid bilayers, PLM forms ion channels selective for Cl-, K+, and taurine. Effluxes of these abundant intracellular osmolytes play an important role in the control of dynamic cell volume changes in many cell types. We measured swelling-activated ion currents and regulatory volume decrease (RVD) in human embryonic kidney cells stably overexpressing canine cardiac PLM. In response to swelling, two clonal cell lines overexpressing PLM had increased swelling-activated ion current densities and faster and more extensive RVD. A third clonal cell line overexpressing mutant PLM showed reduced ion current densities and a diminished RVD response. These results suggest a role for PLM in the regulation of cell volume, perhaps as a modulator of an endogenous swelling-activated signal transduction pathway or possibly by participating directly in swelling-induced osmolyte efflux.

Automated quantitative analysis of angiogenesis in the rat aorta model using Image-Pro Plus 4.1

This paper explains the automated image-processing steps for the quantification of microvascular growth formation in the rat thoracic aortic ring model, an ex vivo model using excised rings of rat aorta embedded in a collagen matrix which produce outgrowths of microvessels. This model of angiogenesis is useful to study the mechanism by which external agents inhibit or stimulate endothelial cell proliferation and tube formation. The manual quantification of blood vessel growth in this model is normally a time-consuming, error prone process. Former automated image analysis methods of the ring model are outdated and cannot be used with current software technology. A macro was created using Image-Pro Plus 4.1 software which was chosen for image analysis because it allows a high degree of control and replication of image-processing steps. The accuracy of this macro was determined by comparing automated counts to manual counts in 161 aortic rings. The square root of the manual count versus the square root of the automated count resulted in a root mean square value of 0.8305.

Effects of phospholemman downregulation on contractility and [Ca(2+)]i transients in adult rat cardiac myocytes

Phospholemman (PLM) expression was increased in rat hearts after myocardial infarction (MI). Overexpression of PLM in normal adult rat cardiac myocytes altered contractile function and cytosolic Ca(2+) concentration ([Ca(2+)](i)) homeostasis in a manner similar to that observed in post-MI myocytes. In this study, we tested whether PLM downregulation in normal adult rat myocytes resulted in contractility and [Ca(2+)](i) transient changes opposite to those observed in post-MI myocytes. Compared with control myocytes infected with adenovirus (Adv) expressing green fluorescent protein (GFP) alone, myocytes infected with Adv expressing both GFP and rat antisense PLM (rASPLM) had 23% less PLM protein (P < 0.012) at 3 days, but no differences were found in sarcoplasmic reticulum (SR) Ca(2+)-ATPase, Na(+)/Ca(2+) exchanger (NCX1), Na(+)-K(+)-ATPase, and calsequestrin levels. SR Ca(2+) uptake and whole cell capacitance were not affected by rASPLM treatment. Relaxation from caffeine-induced contracture was faster, and NCX1 current amplitudes were higher in rASPLM myocytes, indicating that PLM downregulation enhanced NCX1 activity. In native rat cardiac myocytes, coimmunoprecipitation experiments indicated an association of PLM with NCX1. At 0.6 mM [Ca(2+)](o), rASPLM myocytes had significantly (P < 0.003) lower contraction and [Ca(2+)](i) transient amplitudes than control GFP myocytes. At 5 mM [Ca(2+)](o), both contraction and [Ca(2+)](i) transient amplitudes were higher in rASPLM myocytes. This pattern of contractile and [Ca(2+)](i) transient behavior in rASPLM myocytes was opposite to that observed in post-MI rat myocytes. We conclude that downregulation of PLM in normal rat cardiac myocytes enhanced NCX1 function and affected [Ca(2+)](i) transient and contraction amplitudes. We suggest that PLM downregulation offers a potential therapeutic strategy for ameliorating contractile abnormalities in MI myocytes.

A novel method for measuring dynamic changes in cell volume

Many cell types regulate their volume in response to extracellular tonicity changes through a complex series of adaptive mechanisms. Several methods that are presently used to measure cell volume changes include Coulter counters, fluorescent techniques, electronic impedance, and video microscopy. Although these methods are widely used and accepted, there are limitations associated with each technique. This paper describes a new method to measure changes in cell volume based on the principle that fluid flow within a rigid system is well determined. For this study, cos-7 cells were plated to line the inner lumen of a glass capillary and stimulated to swell or shrink by altering the osmolarity of the perfusing solution. The cell capillary was connected in series with a blank reference capillary, and differential pressure changes across each tube were monitored. The advantages of this method include 1) ability to continuously monitor changes in volume during rapid solution changes, 2) independence from cell morphology, 3) presence of physiological conditions with cell surface contacts and cell-cell interactions, 4) no phototoxic effects such as those associated with fluorescent methods, and 5) ability to report from large populations of cells. With this method, we could detect the previously demonstrated enhanced volume regulation of cells overexpressing the membrane phosphoprotein phospholemman, which has been implicated in osmolyte transport.

Gene structure and expression of phospholemman in mouse

Phospholemman (PLM) is a small transmembrane cardiac protein that is the major sarcolemmal substrate for phosphorylation in response to adrenergic stimulation. PLM likely plays a role in muscle contractility and cell volume regulation through its function as a channel or a channel regulator. We are the first to describe the structure of the PLM gene and to demonstrate PLM cDNA splice variants. We cloned the murine PLM cDNA and used it as a probe to isolate the gene from a 129/SvJ genomic library. The gene contains seven introns and eight exons. The coding sequence is interrupted by five introns; the 5' untranslated region by two. Using rapid amplification of 5' cDNA ends we identified transcription start sites and four splice variants of the 5' untranslated domain. There was no TATA box or CAAT box in the putative promoter regions. The gene has several stretches of dinucleotide repeats. The 3' untranslated domains of mouse PLM cDNA clones show sequence differences not accounted for by alternative splicing. Mouse PLM shares 93, 83 and 80% amino acid identity with rat, dog, and human PLMs, respectively. Tissue expression of murine PLM parallels that in other species, being highest in heart, skeletal muscle, and liver.

Dominance of G(s) in doubly G(s)/G(i)-coupled chimaeric A(1)/A(2A) adenosine receptors in HEK-293 cells

A(1) adenosine receptors inhibit adenylate cyclase by activating G(i)/G(o), whereas A(2A) receptors activate G(s). We examined how regions of A(1) and A(2A) receptors regulate coupling to G-proteins by constructing chimaeras in which the third intracellular loops (3ICL or L) and/or the C-termini (or T) were switched. Pertussis toxin (PTX) was used in membrane radioligand binding assays to calculate the fraction of recombinant receptors coupled to G(i)/G(o) and in whole cells to differentially influence agonist-stimulated cAMP accumulation. Switching A(1)/A(2A) 3ICL domains results in receptors that maintain binding selectivity for ligands but are doubly coupled. Receptor chimaeras with an A(1) 3ICL sequence (A(2A)/A(1)L or A(2A)/A(1)LT) respond to agonist stimulation with elevated cAMP despite being coupled predominantly to G(i)/G(o). These chimaeras have basal cAMP levels lower than those of wild-type A(2A) receptors, similar to wild-type A(1) receptors. The A(1) C-terminus modulates the coupling of receptors with A(1) 3ICL such that A(2A)/A(1)LT is better coupled to G(i)/G(o) than A(2A)/A(1)L. The C-terminus has little impact on coupling to receptors containing A(2A) 3ICL sequence. Our results show that the C-terminus sequence selectively facilitates coupling to G(i)/G(o) mediated by A(1) 3ICL and not by other intracellular domains that favour G(i) coupling. The C-terminus sequence has little or no effect on coupling to G(s). For doubly G(s)/G(i)-coupled adenosine receptors in HEK-293 cells, G(s)-mediated stimulation predominates over G(i)/G(o)-mediated inhibition of adenylate cyclase. We discuss the signalling consequences of simultaneously activating opposing G-proteins within single cells.

Airway epithelial CFTR mRNA expression in cystic fibrosis patients after repetitive administration of a recombinant adenovirus

We sought to evaluate the ability of an E1(-), E3(-) adenovirus (Ad) vector (Ad(GV)CFTR.10) to transfer the normal human cystic fibrosis transmembrane conductance regulator (CFTR) cDNA to the airway epithelium of individuals with cystic fibrosis (CF). We administered Ad(GV)CFTR.10 at doses of 3 x 10(6) to 2 x 10(9) plaque-forming units over 9 months by endobronchial spray to 7 pairs of individuals with CF. Each 3-month cycle, we measured vector-derived versus endogenous CFTR mRNA in airway epithelial cells prior to therapy, as well as 3 and 30 days after therapy. The data demonstrate that (a) this strategy appears to be safe; (b) after the first administration, vector-derived CFTR cDNA expression in the CF airway epithelium is dose-dependent, with greater than 5% endogenous CFTR mRNA levels at the higher vector doses; (c) expression is transient, lasting less than 30 days; (d) expression can be achieved with a second administration, but only at intermediate doses, and no expression is observed with the third administration; and (e) the progressive lack of expression with repetitive administration does not closely correlate with induction of systemic anti-Ad neutralizing antibodies. The major advantage of an Ad vector is that it can deliver sufficient levels of CFTR cDNA to the airway epithelium so that CFTR expression protects the lungs from the respiratory manifestations of CF. However, this impressive level of expression is linked to the challenging fact that expression is limited in time. Although this can be initially overcome by repetitive administration, unknown mechanisms eventually limit this strategy, and further repetitive administration does not lead to repetitive expression.

A1 adenosine receptors. Two amino acids are responsible for species differences in ligand recognition

Species differences in ligand binding to A1 adenosine receptors were localized to the seventh transmembrane (TM7) region based on the binding of [8-3H]cyclopentyl-1, 3-dipropylxanthine and three other ligands to wild type and six bovine/canine interspecies receptor chimeras expressed in COS-1 cells. Subsequent site-directed mutagenesis experiments identified amino acid 270 (isoleucine/methionine, bovine/canine) as being primarily responsible for species differences in the binding of N6-adenine-substituted compounds, R-N6-phenylisopropyladenosine (R-PIA) and (S)-N6-endonorbornan-2-yl-9-methyladenine, and the C-8-substituted xanthine, [3H]cyclopentyl-1,3-dipropylxanthine. These data are consistent with the hypothesis that the N6 region of adenines and the C-8-region of xanthines bind to the same region of the receptor. A second TM7 amino acid, 277 (serine/threonine, bovine/canine), selectively influences the binding of the ribose-substituted adenosine analog, 5'-N-ethylcarboxamidoadenosine to a variable extent, depending on the nature of amino acid 270. We hypothesize that amino acid 270 of the A1 receptor interacts with the N6 region of adenosine, while amino acid 277 is important, especially in the absence of an N6 substitution, for interactions with a distinct nucleoside region, possibly on the ribose.

Molecular cloning and functional expression of a sheep A3 adenosine receptor with widespread tissue distribution

Using the polymerase chain reaction, an A3 adenosine receptor has been cloned from the hypophysial par tuberalis of sheep. The clone encodes a 317-amino acid protein that is 72% identical to the rat A3 adenosine receptor. In contrast to rat, where abundant A3 mRNA transcript is found primarily in testis, the sheep transcript is most abundant in lung, spleen, and pineal gland and is present in moderate levels in brain, kidney, and testis. The agonist N6-amino[125I]iodobenzyladenosine binds with high affinity (Kd congruent to 6 nm) and specificity to recombinant A3 adenosine receptors expressed transiently in COS-1 cells or stably in CHO K1 cells. The potency order of agonists is N6-aminoiodobenzyladenosine > N-ethylcarboxamidoadenosine > or = (R)-phenylisopropyladenosine >> cyclopentyladenosine. Little or no binding of purine nucleotides was detected. The potency order of antagonists is 3-(3-iodo-4-aminobenzyl)-8-(4-oxyacetate)phenyl-1- propylxanthine (I-ABOPX) (Ki = 3 nM) > 1,3-dipropyl-8-(4-acrylate)phenylxanthine (BW-A1433) > 1,3-dipropyl-8-sulfophenylxanthine = xanthine amine cogener >> 8-cyclopentyl-1,3-dipropylxanthine. Enprofylline does not bind. These data indicate that, in contrast to A1 adenosine receptors, A3 adenosine receptors preferentially bind ligands with aryl rings in the N6-position of adenine and in the C8-position of xanthine. Among antagonists, the A3 adenosine receptor preferentially binds 8-phenylxanthines with acidic versus basic para-substituents (I-ABOPX > BW-A1433 > 1,3-dipropyl-8-sulfophenylxanthine = xanthine amine cogener). Agonists reduce forskolin-stimulated cAMP accumulation in Chinese hamster ovary cells stably transfected with recombinant sheep A3 adenosine receptors; the reduction is blocked by BW-A1433 but not by 8-cyclopentyl-1,3-dipropylxanthine. These data suggest that (i) A3 adenosine receptors display unusual structural diversity for species homologs, (ii) in contrast to rat, sheep A3 adenosine receptors have a broad tissue distribution, and (iii) some xanthines with acidic side chains bind with high affinity to A3 adenosine receptors.

Cloned receptors and cardiovascular responses to adenosine

Four subtypes of adenosine receptors have recently been cloned from thyroid, brain and testis. In this review we have summarised properties of these purinergic receptors. The cloned A1 and A2 subtypes are probably similar or identical to receptors that exist on cardiac and vascular tissues, respectively. A comparison of the amino acid sequences of A1, A2a, and A2b receptors reveals several stretches of conserved amino acids that are unique to adenosine receptors, primarily in the membrane spanning regions. Species differences in A1 receptors indicate that minor changes in receptor structure can produce marked changes in ligand binding properties and may facilitate the identification of amino acids involved in ligand recognition. A confusing A1 receptor subclassification system of putative A1a, A1b, and A3 subtypes has emerged based on subtle rank order potency differences for various ligands among tissues. cDNAs corresponding to these A1 subtypes have not yet been isolated. Atrial A1 receptors activate K+ channels and inhibit adenylyl cyclase. These two pathways appear to be independently up and down regulated, suggesting the existence either of atrial A1 receptor subtypes or of differential regulation of the coupling of a single receptor to distinct GTP binding proteins. An adenosine receptor distinct from A1 and A2 receptors has been cloned from testis and designated TGPCR, or A3, although it differs from the pharmacologically defined A3 receptor. We suggest that the current A1/A3 receptor subtype nomenclature be abandoned and superseded by a nomenclature based solely on receptor cDNAs. In addition to the cloned adenosine receptors, a novel A4 subtype has been proposed based on pharmacological and electrophysiological criteria.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and expression of a bovine adenosine A1 receptor cDNA

A bovine brain adenosine A1 receptor cDNA encoding a 326 amino acid protein has been identified. This cDNA, which encodes a protein greater than 90% identical to analogous rat and dog receptors, was transiently expressed in COS-1 cells. Recombinant receptors exhibited the features of bovine A1 receptors that distinguish it from rat and canine receptors, including subnanomolar Ki for 1,3-dipropyl-8-cyclopentylxanthine, R-phenylisopropyl- adenosine (R-PIA) and xanthine amino conjugate, and the distinct potency order: R-PIA greater than S-PIA much greater than 5'-N-ethylcarboxamidoadenosine greater than 2'-chloroadenosine. The results indicate that the pharmacological differences between A1 adenosine receptors among species result from only minor differences in receptor structures.

Molecular characterization of a rat alpha 2B-adrenergic receptor

Alpha 2-adrenergic receptors comprise a heterogeneous population based on pharmacologic and molecular evidence. We have isolated a cDNA clone (pRNG alpha 2) encoding a rat alpha 2-adrenergic receptor. A rat kidney cDNA library was screened with an oligonucleotide complementary to a highly conserved region found in all biogenic amine receptors described to date. The deduced amino acid sequence displays many features of guanyl nucleotide-binding protein-coupled receptors except it does not have a consensus N-linked glycosylation site near the amino terminus. Membranes prepared from COS cells transfected with pRNG alpha 2 DNA display high affinity and saturable binding to [3H]rauwolscine (Kd = 2 nM). Competition curve data analysis shows that RNG alpha 2 protein binds to a variety of adrenergic drugs with the following rank order of potency: yohimbine greater than or equal to chlorpromazine greater than or equal to prazosin greater than or equal to clonidine greater than norepinephrine greater than or equal to oxymetazoline. RNG alpha 2 RNA accumulates in both rat kidney and neonatal rat lung (predominant species is 4000 nucleotides). When a cysteine residue (Cys-169) that is conserved among all members of the seven-transmembrane-region superfamily is changed to phenylalanine, the RNG alpha 2 protein fails to bind [3H]rauwolscine after expression in COS cells. We conclude that pRNG alpha 2 likely represents a cDNA for a rat alpha 2B-adrenergic receptor.

Heat stroke in infancy

We observed a 16-month-old infant with residual brain damage following a heat stroke from being left in a parked automobile. In contrast with adults, in whom heat stroke usually follows strenuous exercise, the condition in infants usually results from excessive environmental temperature and/or dehydration. Early recognition of the illness is imperative. Three cardinal freatures are hot, dry skin, central nervous system disturbance, and hyperpyrexia. Immediate treatment should be aimed at improving circulation with volume expanders and rapid cooling. Other supportive measures may be necessary to control seizures, renal failure, hematologic abnormalities, or hepatic involvement.