Biomedical subjects

S A Reading

Publications and source records attributed to S A Reading.

10 recordsLinked to original sources

PubMed2004

TRPC3 mediates pyrimidine receptor-induced depolarization of cerebral arteries.

We tested the hypothesis that TRPC3, a member of the canonical transient receptor potential (TRP) family of channels, mediates agonist-induced depolarization of arterial smooth muscle cells (SMCs). In support of this hypothesis, we observed that suppression of arterial SMC TRPC3 expression with antisense oligodeoxynucleotides significantly decreased the depolarization and constriction of intact cerebral arteries in response to UTP. In contrast, depolarization and contraction of SMCs induced by increased intravascular pressure, i.e., myogenic responses, were not altered by TRPC3 suppression. Interestingly, UTP-evoked responses were not affected by suppression of a related TRP channel, TRPC6, which was previously found to be involved in myogenic depolarization and vasoconstriction. In patch-clamp experiments, UTP activated a whole cell current that was greatly reduced or absent in TRPC3 antisense-treated SMCs. These results indicate that TRPC3 mediates UTP-induced depolarization of arterial SMCs and that TRPC3 and TRPC6 may be differentially regulated by receptor activation and mechanical stimulation, respectively.

Animals↗

PubMed2004

Positive inotropism in mammalian skeletal muscle in vitro during and after fatigue.

We tested the hypothesis that positive inotropic factors decrease fatigue and improve recovery from fatigue in mammalian skeletal muscle in vitro. To induce fatigue, we stimulated mouse soleus and extensor digitorum longus (EDL) to perform isometric tetanic contractions (50 impulses x s(-1) for 0.5 s) at 6 contractions x min(-1) for 60 min in soleus and 3 contractions x min(-1) for 20 min in EDL. Muscles were submerged in Krebs-Henseleit bicarbonate solution (Krebs) at 27 degrees C gassed with 95% nitrogen - 5% carbon dioxide (anoxia). Before and for 67 min after the fatigue period, muscles contracted at 0.6 contractions x min(-1) in 95% oxygen - 5% carbon dioxide (hyperoxia). We added a permeable cAMP analog (N6, 2'-O-dibutyryladenosine 3':5'-cyclic monophosphate at 10(-3) mol x L(-1) (dcAMP)), caffeine (2 x 10(-3) mol x L(-1), or Krebs as vehicle control at 25 min before, during, or at the end of the fatigue period. In soleus and EDL, both challenges added before fatigue significantly increased developed force but only caffeine increased developed force when added during the fatigue period. At the end of fatigue, the decrease in force in challenged muscles was equal to or greater than in controls so that the force remaining was the same or less than in controls. EDL challenged with dcAMP or caffeine at any time recovered more force than controls. In soleus, caffeine improved recovery except when added before fatigue. With dcAMP added to soleus, recovery was better after challenges at 10 min and the end of the fatigue period. Thus, increased intracellular concentrations of cAMP and (or) Ca2+ did not decrease fatigue in either muscle but improved recovery from fatigue in EDL and, in some conditions, in soleus.

Animals↗

PubMed2003

Inotropic effects on mammalian skeletal muscle change with contraction frequency.

Over the last decade, we have attempted to determine if mammalian skeletal muscle's steady-level force development as established by mechanical and stimulation parameters can be increased or decreased by physiological signals. In these experiments, nitric oxide (NO), endothelin-1 (ET-1), adenosine (Ado), and beta-adrenergic agonists (beta) modified force production in the soleus and (or) the extensor digitorum longus (EDL) of the mouse. NO and beta increased the force produced by 0.5-s tetanic contractions at 0.6 contractions/min in both muscles. While EDL did not respond to either Ado or ET-1, the developed force of the soleus was amplified by Ado but attenuated by ET-1. Increased cAMP analogue concentrations amplified developed force in both muscles, but a cGMP analogue had no effect on either muscle. Following an increase in the contraction frequency of the soleus, the increased force in response to NO disappeared, as did the decreased force to ET-1. The increase in force due to a cAMP analogue disappeared during fatigue but reappeared quickly during recovery. Thus, steady-level developed force can be modified by a number of substances that can be released from locations in the body or muscle. The response to a given compound is determined by a complex interaction of metabolic and intracellular signals on the force-generating cascade.

Adrenergic beta-Agonists↗

PubMed2003

Increased cAMP as a positive inotropic factor for mammalian skeletal muscle in vitro.

To test the hypothesis that an increased cAMP concentration improves skeletal muscle force development, we stimulated mouse soleus and extensor digitorum longus (EDL) in the presence of isoproterenol (1 x 10(-5) mol.L-1), a beta-adrenergic agonist, or N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dcAMP) (1 x 10(-3) mol.L-1), a membrane-permeable cAMP analogue. Drugs used in the challenges were dissolved in Krebs-Henseleit bicarbonate buffer (Krebs) at 27 degrees C and gassed with 95% O2 - 5% CO2. Stimulation at 50 impulses.s-1 for 0.5 s produced an isometric tetanic contraction. Over 25 min of contractions at 0.6 contractions.min-1, developed force increased significantly with the addition of isoproterenol (soleus, 2.5% +/- 1.1%; EDL, 13.8% +/- 2.0%) or dcAMP (soleus, 2.3% +/- 0.5%; EDL, 10.9% +/- 1.9%) as compared with vehicle controls (cont) with Krebs added (soleus, 0.0% +/- 0.2%; EDL, -2.5% +/- 0.7%). To investigate the role of Ca2+ availability, we amplified or attenuated sarcolemmal L-type Ca2+ channels with Bay K 8644 (Bay K) (5.6 x 10(-6) mol.L-1) or diltiazem hydrochloride (dilt) (10(-4) mol.L-1), respectively. Ca2+ release from the sarcoplasmic reticulum was increased with caffeine (2 x 10(-3) mol.L-1) or decreased with dantrolene sodium (dant) (4.2 x 10(-7) mol.L-1). With Ca2+availability modified, dcAMP addition in soleus significantly increased force development above control (cont, 2.3% +/- 0.4%; Bay K, 4.0% +/- 1.0%; dilt, 52.3% +/- 3.6%; caffeine, 2.3% +/- 0.7%; dant, 6.0% +/- 2.0%; dilt + dant, 55.0% +/- 23.0%). In EDL, the addition of dcAMP also increased force development above control (cont, 13.7% +/- 1.9%; Bay K, 17.0% +/- 4.0%; dilt, 170.0% +/- 40.0%; caffeine, 23.0% +/- 4.0%; dant, 72.0% +/- 10.0%; dilt + dant, 54.0% +/- 14.0%). Thus, a positive inotropic effect of cAMP existed in both fast- and slow-twitch mammalian skeletal muscle with both normal and altered Ca2+ flux into the sarcoplasm.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed2002

The inotropic effect of nitric oxide on mammalian papillary muscle is dependent on the level of beta1-adrenergic stimulation.

We tested the hypothesis that nitric oxide has a positive inotropic effect on mammalian cardiac muscle contractility and that this effect sums with the positive inotropic effect of beta1-adrenergic agonists when both are present. Feline right ventricular papillary muscles were stimulated to contract isometrically at 0.2 Hz in Krebs-Henseleit bicarbonate buffer (KREBS) gassed with 95% O2 and 5% CO2 (26 degrees C; pH 7.34). The nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP, 10(-5) M), and the membrane permeable cGMP analog 8-bromoguanosine-3',5'-cyclophosphate sodium (Br-cGMP, 10(-5) M), significantly increased developed force by 13.3+/-1.5% (n = 11) and 7.8+/-2.8% (n = 7), respectively. SNAP, at 10(-5) M, significantly increased the force developed by papillary muscle treated with 10(-11) M or 10(-9) M dobutamine hydrochloride (a beta1-adrenergic agonist) (n = 25, 11.3+/-2.9% and 10.0+/-3.6%, respectively) when compared with the addition of KREBS (n = 27, 2.6+/-0.9% and 5.5+/-0.9%), but the increase was less than predicted by the sum of inotropic effects of SNAP and dobutamine. SNAP at 10(-5) M did not change developed force in muscles treated with 10(-7) M dobutamine but it significantly decreased developed force in muscles challenged with 10(-5) M dobutamine (n = 18, 29.3+/-5.0%) when compared with KREBS (n = 10, 41.5+/-6.8%). Similarly, 10(-4) M 8-bromo-adenosine cyclic 3',5'-hydrogen phosphate monosodium (a membrane permeable cAMP analog) increased developed force 14.9+/-3.3% and the addition of 10(-5) M Br-cGMP to those muscles significantly reduced developed force by 3.5%+/-1.1% (n = 7). Thus, the positive inotropic effect of NO decreased and ultimately became an attenuation as the level of beta1-adrenergic stimulation increased due at least in part, to an interaction between the cAMP and cGMP second messenger pathways.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2001

Different effects of a single amino acid substitution on three adjacent epitopes in the gp41 C-terminal tail of a neutralizing antibody escape mutant of human immunodeficiency virus type 1.

The envelope protein of human immunodeficiency virus type 1 (HIV-1) comprises the outer gp 120 SU domain and the anchoring gp41 TM domain, and the conventional view is that it has a single transmembrane region with the following C-terminal sequence situated entirely within the virion. However, we have recently proposed that the gp41 C-terminal region comprises three transmembrane regions and an external loop structure. Part of this loop is the peptide 731PRGPDRPEGIEEEGGERDRDRS752 that carries three antibody epitopes, 734PDRPEG739, 740IEEE743, and 746ERDRD750. PDRPEG is not detected in virions but reacts with its cognate MAb (C8) in Western blots, IEEE is a linear and non-neutralizing epitope, and ERDRD is a conformational and neutralizing epitope. Here we show that escape mutants selected with neutralizing ERDRD-specific antibody had a single 732R-->G substitution, 14 residues upstream of the cognate epitope, and no longer bound the selecting antibody. The same amino acid substitution altered epitope PDRPEG in the virion so that it now reacted with MAb C8, but left epitope IEEE unaffected. Introduction of 732R-->G by site-specific mutagenesis into the gp41 of cloned HIV-1 NL4-3 virions allowed them to escape neutralization by ERDRD-specific IgG, and confirms that 732R makes a major contribution to the neutralizing conformation of the 731-752 region of the C-terminal tail of gp41.

Amino Acid Substitution↗

PubMed2001

Increasing the efficiency of virus infectivity assays: small inoculum volumes are as effective as centrifugal enhancement.

Improving the virus particle:infectious unit ratio is a continuing goal for animal virologists. It is demonstrated for an influenza A virus that decreasing the size of the inoculum volume to 10 microl per well of a 96-well plate was as effective as using centrifugal force with inoculum up to 250 microl. Both achieved a 7.5-fold increase in infectivity in monolayers of MDCK cells compared with standard conditions. The underlying principle of both methods is to bring virus particles into close contact with cell receptors.

Animals↗

PubMed2001

A1 receptor activation decreases fatigue in mammalian slow-twitch skeletal muscle in vitro.

To test the hypothesis that adenosine improves skeletal muscle cell function, we exposed curarized mouse soleus and extensor digitorum longus (EDL) to a range of concentrations of adenosine (10(-9) M to 10(-5) M). Muscles contracted in Krebs-Henseleit bicarbonate buffer (27 degrees C, 95% O2 and 5% CO2) for 500 ms at 50 Hz once every 90 s. Soleus fatigued significantly less with adenosine present at concentrations of 10(-8) M and higher than with the Krebs-Henseleit vehicle control. Adenosine significantly improved force generation or delayed fatigue of EDL only with the initial adenosine challenge. To investigate the receptor population involved, we exposed soleus to agonists specific for A1 receptors (N6-cyclopentyladenosine, CPA), or A2 receptors (CGS 21680 hydrochloride, CGS), or A3 receptors (N6-benzyl-5'-N-ethylcarboxamidoadenosine, BNECA). CPA (A1) significantly decreased fatigue compared with the Krebs-Henseleit vehicle control at concentrations of 10(-9) M and higher. Muscles exposed to the A2 and A3 agonists did not differ from a Krebs-Henseleit plus methanol control. Phenylephrine (10(-6) M), an alpha-adrenergic agonist that increases the concentration of inositol triphosphate (IP3), significantly improved developed force in soleus. Neither a permeable cAMP analog, 8-bromo-cAMP (10(-5) M), nor a beta, agonist, isoproterenol (10(-6) M), had an effect on force generation in the soleus when compared with a saline control. Thus adenosine slowed fatigue in slow-twitch skeletal muscle through A1 receptors.

Adenosine↗

PubMed2001

Contractile function in vitro of slow-twitch skeletal muscle from weanling mice subjected to wasting malnutrition.

Our hypothesis was that malnutrition sufficient to produce weight loss in weanling mice would decrease the ability of slow-twitch skeletal muscle to develop and maintain force. We isolated muscles from 3 groups (n = 5) of weanling C57BL/6J mice of both sexes (i) mice at 19 days of age serving as zero-time or baseline controls (CONT) (ii) mice fed for the next 14 days with a low-protein diet that produces features of incipient kwashiorkor (LPD) and (iii) mice fed for the next 14 days with a complete diet (NORM). Muscles were also obtained from 5 adult mice 7-9 months of age (MAT). We stimulated the soleus at 50 Hz for 500 ms at 0.6 tetanic contractions per min (tet x min(-1)), 6 tet x min(-1), and 30 tet x min(-1) in Krebs-Henseleit bicarbonate buffer at 27 degrees C gassed with 95% O2 and 5% CO2. The initial developed force (mN x mm(-2)) at 0.6 tet x min(-1) did not differ across groups (CONT 211.7 +/- 16.0, LPD 274.2 +/- 41.6, NORM 246.8 +/- 38.0, MAT 210.8 +/- 10.6). The fatigue rate (mN x mm(-2) x min(-1)) at 6 tet x min(-1) was significantly slower in muscles from CONT (0.6 +/- 0.3) and LPD (0.6 +/- 0.4) than in NORM (2.4 +/- 0.6) and MAT (2.3 +/- 0.2). At 30 tet x min(-1), the fatigue rate (mN x mm(-2) x min(-1)) did not differ across groups (CONT 2.4 +/- 0.5, LPD 2.7 +/- 0.5, NORM 2.5 +/- 0.4, MAT 2.0 +/- 0.2). After stimulation at 6 tet x min(-1) and 30 tet x min(-1), only muscles from CONT and LPD recovered to 100%. Because muscles from LPD mice developed equal force, fatigued less, and recovered from fatigue to a greater extent than muscles from NORM mice, we rejected the hypothesis. The function of the tissue remaining in the muscles from LPD mice approximated that of muscles from mice at 19 days of age rather than muscles from either mice of the same age fed a complete diet or adult mice.

Animals↗

PubMed1996

Chromium picolinate.

Chromium picolinate is a dietary supplement gaining in popularity among Americans, especially those seeking a weight-reduction program. Although the mechanism(s) responsible for the purported actions of chromium picolinate have not been thoroughly investigated, studies suggest that the biochemical, physiological, and behavioral actions of chromium picolinate may be a consequence of the effects of picolinic acid on the central nervous system. Analogues of picolinic acid have been shown to induce profound alterations in the metabolism of serotonin, dopamine, and norepnephrine in brain. Thus, caution should be used with chromium picolinate supplements especially by individuals prone to behavioral disorders.

Adult↗