bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of blood pressure and hindlimb conductance during hemorrhage in conscious renal hypertensive rabbits
Authors: Weichert G. , Courneya C. A.
Published: December 2017

We examined the response to hemorrhage in conscious normotensive and hypertensive rabbits under control conditions and during efferent blockade of 1) the hormones vasopressin (AVP) and angiotensin II (ANG II), 2) the autonomic nervous system, and 3) autonomic and hormonal inputs. We recorded mean arterial pressure, heart rate, and hindlimb conductance. The response to hemorrhage was unchanged with hormonal blockade alone. Blockade of the autonomic nervous system caused a faster rate of blood pressure decline, but the rate of decrease in hindlimb conductance was maintained at control levels. Blocking the autonomic nervous system and the hormones resulted in rapid blood pressure decline and an increase in hindlimb conductance. Although the three types of efferent blockade had a similar pattern of effects in normotensive and hypertensive rabbits, hypertensive rabbits exhibited less cardiovascular support during hemorrhage than normotensive rabbits. During hemorrhage, hypertensive rabbits had an attenuation of hindlimb vasoconstriction, a reduction in the heart rate-mean arterial pressure relationship, and reduced ability to maintain blood pressure compared with normotensive rabbits.
Dual effects of external magnesium on action potential duration in guinea pig ventricular myocytes
Authors: Zhang S. , Sawanobori T. , Adaniya H. , Hirano Y. , Hiraoka M.
Published: December 2017

Effects of extracellular magnesium (Mg2+) on action potential duration (APD) and underlying membrane currents in guinea pig ventricular myocytes were studied by using the whole cell patch-clamp method. Increasing external Mg2+ concentration [Mg2+]o) from 0.5 to 3 mM produced a prolongation of APD at 90% repolarization (APD90), whereas 5 and 10 mM Mg2+ shortened it. [Mg2+]o, at 3 mM or higher, suppressed the delayed outward K+ current and the inward rectifier K+ current. Increases in [Mg2+]o depressed the peak amplitude and delayed the decay time course of the Ca2+ current (ICa), the latter effect is probably due to the decrease in Ca(2+)-induced inactivation. Thus 3 mM Mg2+ suppressed the peak ICa but increased the late ICa amplitude at the end of a 200-ms depolarization pulse, whereas 10 mM Mg2+ suppressed both components. Application of 10 mM Mg2+ shifted the voltage-dependent activation and inactivation by approximately 10 mV to more positive voltage due to screening the membrane surface charges. Application of manganese (1-5 mM) also caused dual effects on APD90, similar to those of Mg2+, and suppressed the peak ICa with slowed decay. These results suggest that the dual effects of Mg2+ on APD in guinea pig ventricular myocytes can be, at least in part, explained by its action on ICa with slowed decay time course in addition to suppressive effects on K+ currents.
Myosin light chain kinase phosphorylation in swine carotid artery contraction and relaxation
Authors: Van Riper D. A. , Weaver B. A. , Stull J. T. , Rembold C. M.
Published: December 2017

We investigated the role of myosin light chain kinase (MLCK) phosphorylation in regulating the sensitivity of vascular smooth muscle myosin light chain (MLC) phosphorylation to intracellular Ca2+ concentration ([Ca2+]i). 32PO4-loaded swine carotid arteries were stimulated with histamine or high K+, MLCK was isolated, and the relative phosphorylation of tryptic peptides was measured. In nonlabeled tissues, we measured [Ca2+]i with aequorin, MLCK activity ratio, MLC phosphorylation, and force. A comparison of MLCK phosphorylation on peptide A (mol P in site A/mol MLCK) and MLCK activity ratio showed an inverse relation, suggesting that MLCK site A phosphorylation can regulate the Ca2+ sensitivity of MLCK. MLCK site A phosphorylation and MLCK activity ratio depended on [Ca2+]i. Histamine stimulation yielded greater MLC phosphorylation than high K+ stimulation over a range of [Ca2+]i; however, there were no apparent stimulus-dependent differences in MLCK phosphorylation, suggesting that stimulus-dependent differences in the Ca2+ sensitivity of MLC phosphorylation are not based on differences in MLCK phosphorylation. We also determined whether MLCK phosphorylation was involved in adenosine 3',5'-cyclic monophosphate-mediated relaxation. In histamine-contracted tissues, forskolin decreased [Ca2+]i, MLC phosphorylation, and force. MLCK phosphorylation decreased to an extent consistent with the decrease in [Ca2+]i. In KCl-stimulated tissues, forskolin did not alter [Ca2+]i or increase MLCK phosphorylation but forskolin did decrease MLC phosphorylation. Thus, in swine carotid artery, MLCK phosphorylation appears to be regulated exclusively by Ca2+ and plays little role in stimulus-dependent differences in Ca2+ sensitivity of MLC phosphorylation or in mediating forskolin-induced relaxation.
Calcium currents of ventricular cell pairs during action potential conduction
Authors: Kumar R. , Joyner R. W.
Published: December 2017

We have studied the L-type calcium current that occurs during action potential conduction between an isolated pair of guinea pig ventricular cells. To accomplish this, we first recorded action potentials from the leader cell (stimulated cell, cell 1) and the follower cell (nonstimulated cell, cell 2) with a fixed coupling resistance between the cells supplied by a coupling clamp circuit. We then applied these recorded action potentials as command potential waveforms for other cells studied in the voltage-clamp mode in which internal and external solutions that isolated the L-type calcium current were used. The action potential waveform of the leader cell had a rapid upstroke and then a partial repolarization during the conduction delay before activation of the follower cell. The L-type calcium current occurred with a large magnitude during the conduction delay for the leader cell but not for the follower cell. This leads to an asymmetry of calcium current for the two cells, with greater calcium current for the leader cell than for the follower cell. When we reversed the direction of conduction for cell 1 and cell 2 by stimulating cell 2, we found that application of these recorded waveforms for the action potentials for cell 1 and cell 2 to the voltage-clamped cells also reversed the asymmetry of the magnitude of the calcium current. We conclude that discontinuous conduction in cardiac tissue is associated with a directionally determined asymmetry in the magnitude of the calcium current, with the leader cell experiencing a greater peak calcium current than the follower cell.
Developmental changes of action potential configuration and I(to) in canine epicardium
Authors: Pacioretty L. M. , Gilmour R. F.
Published: December 2017

Developmental changes of the transient outward current (I(to)) and action potential configuration were determined in canine epicardium ranging in age from fetal to 60 wk. The contributions of I(to) to rapid initial repolarization and to terminal repolarization were estimated by measuring the amplitude of phase 1 of the action potential and action potential duration, respectively. Phase 1 amplitude decreased progressively from fetal to 40 wk and remained constant thereafter. Action potential duration decreased from fetal to 2 wk, increased to 20 wk, and tended to decrease thereafter. Peak I(to) at +40 mV increased progressively from 2 to 60 wk. However, I(to) density was less at 2-10 wk than at 20-60 wk. The time constant of decay of I(to) increased with age from 2 to 60 wk, whereas the steady-state voltage dependence of inactivation did not vary with age. The time constant for the initial rapid phase of recovery from inactivation decreased from 2 to 10 wk and remained constant thereafter. The time constant for the more slowly evolving phase did not vary with age. The observation that the age-dependent reduction in phase 1 amplitude did not necessarily coincide with significant increases in I(to) density suggests that maturation of other ionic currents or transport mechanisms may contribute to developmental alterations of phase 1 repolarization.
Modification of cerebral laser-Doppler flow oscillations by halothane, PCO2, and nitric oxide synthase blockade
Authors: Hudetz A. G. , Smith J. J. , Lee J. G. , Bosnjak Z. J. , Kampine J. P.
Published: December 2017

We investigated whether nitric oxide (NO) played a role in the generation of cerebrocortical flow oscillations and their modification by hypocapnia, hypercapnia, and halothane administration. Parietal cortical laser-Doppler flow (LDF) was monitored transcranially in anesthetized (barbiturate + 0-1.0% halothane), artificially ventilated, adult male Sprague-Dawley rats. Thirty minutes after infusion of N omega-nitro-L-arginine methyl ester (L-NAME, 20 mg/kg i.v.) mean arterial pressure (MAP) increased from 105 +/- 10 to 132 +/- 15 mmHg (P < 0.02), while mean LDF decreased from 159 +/- 36 to 135 +/- 30 perfusion units (PU, P < 0.05). Oscillations in LDF at a frequency of 6.3-7.8 cycles/min and amplitude of 10% were induced or augmented by L-NAME but not by D-NAME or indomethacin (2 mg/kg i.p.). L-arginine (200 mg/kg) abolished the oscillations post-L-NAME at constant MAP. Sodium nitroprusside infusion (10(-5) M, 5-50 microliters/min) reversed the L-NAME-induced increase in MAP and decrease in mean LDF but did not attenuate the flow oscillations. Hypocapnia post-L-NAME decreased LDF to 110 +/- 20 PU (P < 0.001) and augmented the flow oscillations (amplitude: 11-31%). Hypercapnia (5% CO2) or halothane (0.4-1.0%) suspended the oscillations in the presence of L-NAME. The results suggest that NO synthase activity inhibits cerebrocortical flow oscillations, and NO is not an obligatory mediator of the effects of halothane, hypocapnia, and hypercapnia on oscillatory activity.
Timing of sympathetic innervation affects growth of myocardium in oculo
Authors: Love T. C. , Tucker D. C.
Published: December 2017

The effects of sympathetic innervation on myocardial growth during the proliferative and hypertrophic phases of cardiac growth were examined with the use of embryonic day 12 whole hearts or ventricles cultured in the anterior eye chamber of adult rats for 8 wk. Sympathetic innervation of whole heart and ventricular grafts was prevented by removing the superior cervical ganglion 1 wk before grafting or was limited to the cellular proliferation phase of growth by superior cervical ganglionectomy after grafts had been in oculo for 4 wk. Grafts in sympathetically innervated eye chambers were significantly larger than grafts in eye chambers denervated at 4 wk and grafts in eye chambers sympathectomized 1 wk before grafting. Innervation of grafts was delayed until 5-6 wk in oculo by crushing the internal carotid nerve. Delayed innervation produced grafts that were as large as those in innervated eye chambers. Together, these experiments suggest that the effects of sympathetic innervation on myocardial growth in oculo are most apparent during the second 4 wk in oculo (i.e., during the cellular enlargement phase of growth.
Arginine-nitric oxide pathway and cerebrovascular regulation in cortical spreading depression
Authors: Fabricius M. , Akgoren N. , Lauritzen M.
Published: December 2017

Nerve cells release nitric oxide (NO) in response to activation of glutamate receptors of the N-methyl-D-aspartate (NMDA) subtype. We explored the hypothesis that NO influences the changes of cerebral blood flow (CBF) during cortical spreading depression (CSD), which is known to be associated with NMDA receptor activation. CBF was monitored in parietal cortex by laser-Doppler flowmetry in halothane-anesthetized rats. Under control conditions, CSD induced regular changes of CBF, which consisted of four phases: a brief hypoperfusion before the direct current (DC) shift; a marked CBF rise during the DC shift; followed by a smaller, but protracted increase of CBF; and a prolonged CBF reduction (the oligemia). NO synthase inhibition by intravenous and/or topical application of NG-nitro-L-arginine enhanced the brief initial hypoperfusion, but the CBF increases and the oligemia were unchanged. L-Arginine prevented the development of the prolonged oligemia after CSD but had no influence on the marked rise of CBF during CSD. Animals treated with L-arginine recovered the reduced vascular reactivity to hypercapnia after CSD much faster than control rats. Functional denervation of cortical and pial arterioles by tetrodotoxin accentuated the pre-CSD hypoperfusion and the oligemia but did not affect the CBF increases. The results suggest that NO is important for the changes of cerebrovascular regulation following CSD. The observations may have clinical importance, since CBF changes during migraine may be triggered by CSD.
Depressed regional deformation near anterior papillary muscle
Authors: Holmes J. W. , Takayama Y. , LeGrice I. , Covell J. W.
Published: December 2017

The role of the papillary muscle in left ventricular function has received new attention. We hypothesized that regional mechanics of the left ventricular wall near the anterior papillary muscle are influenced by the papillary muscle insertion. We therefore studied three-dimensional regional mechanics in and near the anterior papillary muscle in anesthetized, open-chest dogs, using implanted radiopaque markers and biplane cineradiography. In seven dogs, deformation differed little between an anterior papillary muscle insertion site (PMA) and a more basal site (PMB) overlying the anterior papillary muscle. However, local shortening and wall thickening were depressed in both locations relative to anterior free wall sites (FWA, FWB) studied in five additional dogs. A distinct structural border was observed at the junction between the myocardial wall and anterior papillary muscle, which may preclude the use of homogeneous strain in that region. Data from within the anterior papillary muscle indicated that uniaxial measurements in the papillary muscle are extremely sensitive to the orientation of the measurement axis, possibly explaining the variety of papillary muscle shortening patterns reported by previous investigators.
Effect of exercise on coronary pressure-flow relationship in hypertrophied left ventricle
Authors: Duncker D. J. , Zhang J. , Pavek T. J. , Crampton M. J. , Bache R. J.
Published: December 2017

Left ventricular (LV) hypertrophy (LVH) secondary to chronic pressure overload is associated with increased susceptibility to myocardial hypoperfusion and ischemia during exercise. The present study was performed to determine whether exercise causes alterations in minimum coronary resistance or effective back pressure [coronary pressure at zero flow (Pzf)] that limit maximum myocardial perfusion in the hypertrophied heart. Ascending aortic banding in 7 dogs increased the LV weight-to-body weight ratio to 7.7 +/- 0.3 g/kg compared with 4.6 +/- 0.2 g/kg in 11 normal dogs (P < 0.01). Maximum coronary vasodilation was produced by intracoronary infusion of adenosine. Under resting conditions, the slope of the pressure-flow relationship (conductance) was significantly lower in the LVH animals than in the normal dogs (7.2 +/- 0.8 vs. 11.9 +/- 0.8 x 10(-2) ml.min-1.g-1.mmHg-1; P < 0.01); the slope correlated with the degree of hypertrophy r = 0.74; P < 0.001). The Pzf measured during total coronary artery occlusion (Pzf,measured) was significantly elevated in LVH compared with normal dogs (25.6 +/- 2.2 vs. 13.0 +/- 1.2 mmHg; P < 0.01); Pzf,measured was positively correlated (r = 0.78, P < 0.0005) with LV end-diastolic pressure measured during total coronary artery occlusion (9.0 +/- 1.1 mmHg in normal dogs and 22.2 +/- 3.2 mmHg in LVH dogs; P < 0.01). Graded treadmill exercise to maximum heart rates of 210 +/- 9 and 201 +/- 8 beats/min in normal and LVH animals, respectively, caused similar decreases in the slope of the pressure-flow relationship in LVH (from 7.7 +/- 0.9 to 6.1 +/- 0.8 x 10(-2) ml.min-1.g-1.mmHg-1; P < 0.01) and normal dogs (from 11.9 +/- 0.8 to 10.0 +/- 0.7 x 10(-2) ml.min-1.g-1.mmHg-1; P < 0.01). However, exercise-induced increases in Pzf,measured were significantly greater in the LVH animals (from 25.6 +/- 2.2 to 40.8 +/- 2.1 mmHg; P < 0.01) than in normal animals (from 13.0 +/- 1.2 to 24 +/- 2.1 mmHg; P < 0.01) (P < 0.01 LVH vs. normal). The greater increase in Pzf paralleled a more pronounced increase in LV end-diastolic pressure in the LVH dogs from 22.2 +/- 3.2 to 39.1 +/- 2.7 mmHg) than in normal dogs from 9.0 +/- 1.1 to 14.2 +/- 2.0 mmHg). The results suggest that exaggerated increases in filling pressure during exercise in the hypertrophied left ventricles contributed to impairment of myocardial perfusion during exercise by augmenting the back pressure, which opposes coronary flow.(ABSTRACT TRUNCATED AT 400 WORDS)
Adenosine modulates hypoxia-induced atrial natriuretic peptide release in fetal sheep
Authors: Ogunyemi D. A. , Koos B. J. , Arora C. P. , Castro L. C. , Mason B. A.
Published: December 2017

The effects of adenosine on atrial natriuretic peptide (ANP) secretion were determined in chronically catheterized fetal sheep (> 0.8 term). Adenosine was infused into the the right jugular vein for 1 h at 8 +/- 0.4 (5 fetuses), 160 +/- 8 (6 fetuses), and 344 +/- 18 micrograms.min-1.kg estimated fetal wt-1. Fetal arterial blood gases and pH were generally unaffected by adenosine, although mean arterial CO2 tension increased transiently by 2-5 Torr and pH fell progressively during the highest rate of infusion. During the intermediate and high infusion rates, fetal hemoglobin concentrations increased by 11-13% and mean fetal heart rate rose by 18% from a control value of approximately 167 beats/min. Mean arterial pressure was not affected during adenosine infusion. Adenosine significantly increased fetal plasma ANP levels, with maximum concentrations 1.80, 2.36, and 2.51 times greater than control means (142-166 pg/ml) for the respective infusion rates of 8, 160, and 344 micrograms.min-1.kg estimated fetal wt-1. In seven fetuses, reducing fetal arterial O2 tension by approximately 9-10 Torr from a control of 23 +/- 1.3 Torr increased plasma ANP concentrations approximately 2.4 times the control mean of 176 pg/min. Adenosine-receptor blockade with 8-(p-sulfophenyl)-theophylline reduced by 50% the maximum hypoxia-induced rise in plasma ANP concentrations. It is concluded that adenosine causes a dose-dependent rise in fetal plasma ANP concentrations and modulates fetal ANP release during hypoxia.
Effect of nitric oxide synthase inhibition on postischemic cerebral hyperemia
Authors: Greenberg R. S. , Helfaer M. A. , Kirsch J. R. , Traystman R. J.
Published: December 2017

We tested the hypothesis that inhibition of nitric oxide synthase (NOS) activity in brain before ischemia decreases postischemic hyperemia. Pentobarbital-anesthetized piglets underwent 15 min of complete global cerebral ischemia induced by elevation of intracranial pressure followed by 20 min of reperfusion. Before ischemia the animals were randomly assigned to receive either intravenous N omega-nitro-L-arginine methyl ester (L-NAME 10 mg/kg, n = 6, or 50 mg/kg, n = 6) or an equal volume of saline (10 ml, n = 8). Serial cerebral blood flow (radiolabeled microspheres) was measured at baseline and during ischemia and reperfusion. Forebrain postischemic hyperemia was documented after administration of saline (42 +/- 4 to 88 +/- 10 ml.min-1.100 g-1) and 10 mg/kg L-NAME (36 +/- 4 to 59 +/- 9 ml.min-1.100 g-1) but not after 50 mg/kg L-NAME (29 +/- 3 to 34 +/- 7 ml.min-1.100 g-1). However, the percent reduction in cerebral vascular resistance (CVR) fell during reperfusion to a similar extent in all three groups because of differences between groups in cerebral perfusion pressure changes during the protocol. CVR fell to the lowest level at 8 min of reperfusion in the saline-treated animals (2.0 +/- 0.16 to 0.68 +/- 0.05 mmHg.ml-1.min.100 g) compared with the L-NAME-treated animals (50 mg/kg: 4.0 +/- 0.3 to 1.8 +/- 0.2 mmHg.ml-1.min.100 g).(ABSTRACT TRUNCATED AT 250 WORDS)
Participation of hypothalamic paraventricular nucleus in locus ceruleus-induced baroreflex suppression in rats
Authors: Shih C. D. , Chan S. H. , Chan J. Y.
Published: December 2017

We evaluated the potential role of the paraventricular nucleus (PVN) of the hypothalamus in the suppression of baroreceptor reflex (BRR) response by locus ceruleus (LC), using adult male Sprague-Dawley rats anesthetized with pentobarbital sodium. Electrical stimulation of histologically verified sites in the LC elicited significant reduction in the BRR response. This suppressive effect of LC on BRR response was appreciably antagonized by bilateral electrolytic lesions of the PVN and reversibly blocked by bilateral microinjection of 2% lidocaine into similar hypothalamic loci. Local administration of the alpha 1-adrenoceptor antagonist, prazosin (50 pmol), or an antiserum directed against neuropeptide Y (NPY) (1:20) into the bilateral PVN also significantly attenuated the suppression elicited by LC on BRR response. In contrast, treatments with the alpha 2-adrenoceptor blocker, yohimbine (50 pmol), heat-inactivated NPY antiserum (1:20), artificial cerebrospinal fluid, or normal rabbit serum (1:20) produced no discernible effect. These results suggest that the PVN may constitute part of the efferent pathways through which LC elicits its inhibition on the BRR response. Furthermore, LC may activate this pathway via alpha 1-adrenoceptors and NPY receptors in the PVN.
Role of cyclooxygenase metabolites in mediating platelet-induced baroreceptor dysfunction
Authors: Li Z. , Su X. , Chapleau M. W.
Published: December 2017

The goal of the study was to determine the role of cyclooxygenase metabolites in mediating platelet-induced suppression of baroreceptor activity. Exposure of the isolated carotid sinus of rabbits to thrombin-activated rabbit platelets (3 x 10(8) cells/ml Krebs buffer) decreased baroreceptor activity (P < 0.05) without significantly altering the slope of the pressure-activity relation (gain). The platelet-induced suppression of activity was not blocked but instead was even more pronounced after inhibition of cyclooxygenase with indomethacin; both maximum baroreceptor activity and gain were decreased markedly. The exacerbation of platelet-induced baroreceptor dysfunction contrasted with equivalent carotid vasoconstrictor responses to platelets before and after indomethacin. Furthermore, the stable thromboxane (TxA2) mimetic U-46619 caused similar vasoconstriction as platelets but did not influence baroreceptor gain or maximum activity. In contrast to indomethacin, the selective TxA2 synthesis inhibitor and receptor blocker CGS-22652 failed to influence platelet-induced suppression of activity. In summary, 1) rabbit platelet aggregating in carotid sinus suppress baroreceptor activity, which cannot be explained by the vasoconstriction, and 2) the suppression of activity is not mediated by TxA2 from platelets and is opposed by prostacyclin (PGI2) or other prostanoids produced in carotid sinus. The combination of impaired formation of PGI2 and platelet activation in atherosclerotic and thrombotic states may lead to profound baroreceptor dysfunction.
Complexity of chaotic vasomotion is insensitive to flow and pressure but can be regulated by external control
Authors: Griffith T. M. , Edwards D. H.
Published: December 2017

We have previously shown that irregular vasomotion induced by histamine in isolated rabbit ear resistance arteries is chaotic. Consistently, in the present study, such activity was found to respond in a highly unpredictable fashion to changes in flow under conditions of controlled-flow perfusion, although its fractal dimension, calculated by a standard correlation technique, was effectively independent of flow rate and remained < 4. As this statistic provides an estimate of the number of control variables that generate a chaotic time series, flow thus appears to modulate vasomotion without fundamentally contributing to its genesis. External modification of the dynamics was attempted by a negative feedback loop that regulated pump speed through an error signal derived from perfusion pressure. Irregular responses were converted to either periodic or steady-state behavior in approximately 60% of cases with an associated fall in fractal dimension. Conversely, unsuccessful control was often associated with an increase in fractal dimension, reflecting the additional complexity introduced by the feedback loop. Furthermore, control was more readily achieved in the presence of NG-nitro-L-arginine methyl ester, when time- and flow-dependent changes in endothelium-derived relaxing factor synthesis would not be expected to complicate the overall dynamics. The study suggests that vascular chaos may be economically "controlled" under both physiological and pathophysiological conditions.
Force, not sarcomere length, correlates with prolongation of isosarcometric contraction
Authors: Janssen P. M. , Hunter W. C.
Published: December 2017

Recent studies have emphasized the importance of the late systolic phase for understanding ventricular ejection. To examine the myocardial factors controlling this phase, we studied the timing of twitch contraction in nine excised rat trabeculae contracting isosarcometrically. By varying both sarcomere length (SL) and extracellular Ca2+ concentration ([Ca2+]) we determined which of these factors or the developed peak twitch force correlated better with the prolongation of contraction. We focused on the period from just before the peak of force to the time of half relaxation. SL was measured by laser diffraction and kept constant using adaptive control. Peak twitch force was the factor most tightly correlated with prolongation of contraction: as force rose from 10 to 100 mN/mm2, duration tripled from 100 to 300 ms. When the trend with force was removed, however, no separate influence of SL remained. Increase in [Ca2+]o abbreviated contraction equally at all force levels. Prolongation of late systolic contraction was also highly correlated with prolongation of the time constant for late relaxation, suggesting a common mechanism by which peak twitch force lengthens the entire subsequent time course of a twitch. We hypothesize that 1) increased force correlates with prolonged Ca2+ binding to troponin-C, and/or 2) attached cross bridges act cooperatively to oppose the inhibiting effects of tropomyosin as Ca2+ is lost from the thin filaments.(ABSTRACT TRUNCATED AT 250 WORDS)
An ATP-activated nonselective cation channel in guinea pig ventricular myocytes
Authors: Parker K. E. , Scarpa A.
Published: December 2017

Extracellular ATP released from nerves onto vascular smooth muscle or released from damaged tissues during traumatic injury, shock, or ischemia profoundly alters cardiovascular physiology. We have used patch-clamp methods to investigate the effects of extracellular ATP on guinea pig ventricular myocytes because guinea pigs are a commonly used model for the study of cardiac electrophysiology. We have found that ATP activates a rapid, desensitizing, inward current. This inward current is activated by a P2 receptor that does not conform to published receptor subclasses. A concentration of 100 microM ATP activates more current than 100 microM alpha, beta-methyleneadenosine 5'-triphosphate, which in turn activates more current than 100 microM ADP. 2-Methylthioadenosine 5'-triphosphate (2-MeS-ATP) and adenosine 5'-O-(3-thiotriphosphate) are also effective agonists. Adenosine, AMP, guanosine 5'-triphosphate, and uridine 5'-triphosphate are ineffective at 100 microM. The inward conductance has a reversal potential near 0 mV and in ion-substitution experiments was found to be carried through nonselective cation channels rather than chloride channels. The conductance has inwardly rectifying current-voltage (I-V) relations. When ATP is used as the agonist, fluctuation analysis yields an apparent unitary conductance of 0.08 pA at a holding potential of -120 mV with sodium as the main charge-carrying ion. The combination of inwardly rectifying I-V relations, the efficacy of 2-MeS-ATP, and the very low conductance distinguish this conductance from other ATP-activated nonselective channels, including those recently cloned from rat vas deferens and PC-12 cells.
Primary negativity does not predict dominant pacemaker location: implications for sinoatrial conduction
Authors: Bromberg B. I. , Hand D. E. , Schuessler R. B. , Boineau J. P.
Published: December 2017

Activation sequence maps derived during normal sinus rhythm from extracellular potentials in the canine right atrium exhibit widely separated sites of origin. The objectives of this study were to characterize the distribution of pacemakers within the right atrium and to determine the relationship of pacemaker action potentials to sites of earliest surface activation as well as to local extracellular electrograms. The right atria of six adult mongrel dogs were rapidly excised under deep pentobarbital sodium anesthesia and perfused with 95% O2-5% CO2 Krebs-Henseleit solution. Action potentials from the epicardial surface were recorded throughout the region bounded by the crista terminalis laterally and the atrial septum medially. Simultaneously, unipolar extracellular electrograms were recorded from 250 endocardial sites. The earliest pacemakers preceded the earliest electrogram by 63 +/- 34 ms; the latest pacemakers followed the earliest electrogram by 71 +/- 40 ms. Primary negativity in the extracellular electro gram did not predict the site of the earliest or dominant pace maker and in some cases was associated with the latest pace makers. We conclude that primary negativity and/or the sites of earliest activation reflect the point at which the impulse engages atrial myocardium, not the site of earliest pacemaker activity. As such, early extracellular activation appears to represent sites of exit from a relatively insulated sinus node.
Sarcoplasmic reticulum in cardiac length-dependent activation in rabbits
Authors: Bluhm W. F. , Lew W. Y.
Published: December 2017

After a step increase in length of rabbit right ventricular papillary muscles, active stress increased immediately followed by a further slow increase in stress over 15-20 min. We studied the contribution of the sarcoplasmic reticulum (SR) to the slow change in stress (SCS) after changing muscle length from 85 to 95% of length at which active force development was maximal. SCS amounted to 32.5 +/- 12.2% mean +/- SD, n = 19) of the total increase in active stress. This was associated with a 13.2 +/- 8.7% increase in calcium content of the SR as estimated with rapid cooling contractures (P < 0.0001, n = 19). However, SCS was not dependent on SR calcium content. There was no significant attenuation in SCS after SR calcium depletion with ryanodine (n = 6), SR Ca(2+)-adenosinetriphosphatase inhibition with cyclopiazonic acid (n = 6), or combined treatment with ryanodine and cyclopiazonic acid (n = 3). We conclude that, in the rabbit, SR calcium content increases slowly after a step increase in cardiac muscle length but the slow changes in active stress are not dependent on the sarcoplasmic reticulum.
NBT reactivity correlates to the distribution of PMNs between rat pulmonary and systemic circulation
Authors: Wikstrom T. , Braide M. , Bagge U. , Risberg B.
Published: December 2017

The rat systemic and pulmonary vascular transit times of radiolabeled polymorphonuclear granulocytes (experimental population referred to as “Polys”) and mononuclear leukocytes (experimental population referred to as “Monos”) (111In) in relation to those of erythrocytes (51Cr) were measured under physiological conditions. Results were also expressed as “circulating” pool and “marginated” pool of the two leukocyte fractions, and it was investigated whether the degree of spontaneous granulocyte activation, measured with the nitro blue tetrazolium (NBT) reduction test, was of importance for the retention of Polys in the lungs. The measured mean vascular transit was similar for Monos and Polys and several times slower than that of the erythrocytes in the pulmonary (17.4 times) and the systemic (4.1 times) vascular beds. The percentage of NBT-positive cells was < 10% in most animals, indicating a low level of spontaneous granulocyte activation. Increasing levels of NBT-positive cells correlated with a redistribution of granulocytes from the systemic marginated cell pool to the pulmonary marginated cell pool. Microscopic evaluation of sections from embedded lung tissue biopsies, obtained after intravital staining of the leukocytes, confirmed the isotope data on pulmonary transit.
Restoration of normal pH triggers ischemia-reperfusion injury in lung by Na+/H+ exchange activation
Authors: Moore T. M. , Khimenko P. L. , Taylor A. E.
Published: December 2017

The effects of acidotic extracellular pH and Na+/H+ exchange inhibition on ischemia-reperfusion (I/R)-induced microvascular injury were studied in the isolated, buffer-perfused rat lung. When lungs were subjected to 45 min of ischemia followed by 30 min of reperfusion, the capillary filtration coefficient (Kfc) increased significantly, resulting in a change in Kfc (delta Kfc) of 0.360 +/- 0.09 ml.min-1.cmH2O-1.100 g-1. Addition of hydrochloric acid to the perfusate before ischemia at a concentration sufficient to reduce perfusate pH from 7.38 +/- 0.03 to 7.09 +/- 0.04 completely prevented the increase in Kfc associated with I/R (delta Kfc = 0.014 +/- 0.034 ml.min-1.cmH2O-1.100 g-1). Addition of a Na+/H+ exchange inhibitor, 5-(N,N-dimethyl)-amiloride, to the perfusate either before ischemia or at reperfusion also prevented the I/R-induced permeability increase (delta Kfc = 0.01 +/- 0.02 and -0.001 +/- 0.02 ml.min-1.cmH2O-1.100 g-1, respectively). We conclude that restoration of flow at physiological pH to the postischemic lung activates the Na+/H+ exchange system, which may represent the “triggering mechanism” responsible for initiating reperfusion-induced microvascular injury.
Reduced threshold for myocardial cell calcium intolerance in the rat heart with aging
Authors: Hano O. , Bogdanov K. Y. , Sakai M. , Danziger R. G. , Spurgeon H. A. , Lakatta E. G.
Published: December 2017

To determine whether advancing age is accompanied by a reduced Ca2+ tolerance, we measured Ca(2+)-dependent diastolic pressure, prolonged relaxation and systolic functional deterioration, spontaneous sarcoplasmic reticulum (SR)-generated Ca2+ oscillations [detected as scattered laser light intensity fluctuations (SLIF)], aftercontractions, and ventricular fibrillation in isolated, isovolumic, atrioventricular-blocked intact hearts from 24- to 26-mo (old) and 6- to 8-mo (young) male Wistar rats. In enzymatically isolated single cardiac myocytes, the likelihood of the occurrence of spontaneous contractile waves driven by spontaneous SR Ca2+ release was also determined. In response to stepwise increase in perfusate Ca2+ concentration (Cao), a reduction in the maximum developed pressure accompanied by an elevation in end-diastolic pressure and a prolonged contraction duration was observed at lower Cao in old vs. young hearts (P < 0.01 for each parameter). Furthermore, Ca(2+)-dependent ventricular fibrillation occurred during pacing in six old but in no young hearts (P < 0.01), aftercontractions were observed in seven old vs. one young heart (P < 0.01), and SLIF increased to a greater extent in old vs. young hearts. In single cardiac myocytes, spontaneous contractile waves occurred more frequently with increasing age (P < 0.01). These results indicate that aging is associated with an increased likelihood for the occurrence of SR-generated Ca2+ oscillations and functional abnormalities that result from these oscillations.
Mechanisms of hemolysate-induced [Ca2+]i elevation in cerebral smooth muscle cells
Authors: Zhang H. , Weir B. , Marton L. S. , Macdonald R. L. , Bindokas V. , Miller R. J. , Brorson J. R.
Published: December 2017

The effects of hemolysate on free cytosolic [Ca2+] ([Ca2+]i) homeostasis were studied in freshly isolated rat basilar artery smooth muscle cells using fura 2 and dual excitation wavelength microfluorimetry. Hemolysate reversibly produced a transient [Ca2+]i peak followed by a slowly decaying plateau which was absent in Ca(2+)-free solution. This effect of hemolysate was attenuated by 1) the sarcoplasmic reticulum Ca2+ pump inhibitors thapsigargin and cyclopiazonic acid, 2) the Ca2+ release-blocking agents ryanodine and dantrolene, 3) the cytochrome P-450 inhibitor econazole, and 4) the inorganic Ca2+ channel blocker lanthanum but was not significantly attenuated by 1) the receptor-regulated Ca2+ channel blocker SKF-96365 or 2) the voltage-dependent Ca2+ channel blocker nimodipine. Fractionation of hemolysate using membranes with specific pore sizes (0.5, 1, and 12-14 kDa) indicated that a component(s) > 0.5 but < 1 kDa could produce a similar [Ca2+]i peak and plateau while fractions > 1 and > 12-14 kDa produced a small and slow [Ca2+]i rise without a significant peak. ATP, which was found in hemolysate, produced a [Ca2+]i response similar to that of hemolysate. P2-purinoceptor antagonists significantly attenuated the effect of ATP, hemolysate, and the fractions < 1 and < 12-14 kDa. We conclude that hemolysate elevates [Ca2+]i by both releasing Ca2+ from internal stores and triggering Ca2+ entry, possibly from a voltage-independent Ca2+ influx pathway, an effect apparently identical to that of ATP.
Cerebral O2 transport with hematocrit reduced by cross-linked hemoglobin transfusion
Authors: Ulatowski J. A. , Bucci E. , Nishikawa T. , Razynska A. , Williams M. A. , Takeshima R. , Traystman R. J. , Koehler R. C.
Published: December 2017

The purpose of this study was to dissociate effects of reduced viscosity from those of low arterial O2 content (CaO2) on cerebral blood flow (CBF) during anemia. Three groups (n = 8) of pentobarbital sodium-anesthetized cats were studied: 1) a time-control group with a hematocrit of 32 +/- 1% (SE), 2) an anemia group that underwent an isovolumic exchange transfusion with albumin in a salt solution to decrease hematocrit to 18 +/- 1%, and 3) a group transfused with cell-free, tetramerically stabilized hemoglobin to decrease hematocrit equivalently to that in the albumin-transfused group. CaO2 (in ml/dl) in the hemoglobin-transfused group (11.8 +/- 0.3) and the control group (15.0 +/- 0.6) was greater than that in the albumin group (8.7 +/- 0.3). CBF (in ml.min-1.100 g-1) in the hemoglobin group (45 +/- 3) and control group (36 +/- 4) was less than that in the albumin group (60 +/- 3). Consequently, cerebral O2 transport (CaO2 x CBF) was similar in the hemoglobin, control, and albumin groups (5.3 +/- 0.3, 5.3 +/- 0.4, and 5.2 +/- 0.2 ml.min-1.100 g-1, respectively). After infusion of N omega-nitro-L-arginine methyl ester (L-NAME) to inhibit nitric oxide (NO) synthase, CBF in the hemoglobin group remained lower than that in the albumin group, suggesting that NO scavenging by hemoglobin did not solely account for the lower CBF. In contrast, the neurohypophysis (posterior pituitary) exhibited substantial decreases in blood flow that were not augmented by L-NAME administration after hemoglobin transfusion and that were similar in magnitude to L-NAME alone. Thus NO scavenging by cell-free hemoglobin may be more prominent in high-flow, protein-permeable regions enriched with NO synthase. These results support the hypothesis that O2 transport to cerebrum is well regulated when CaO2 is manipulated independently of hematocrit and viscosity.
Ca2+ transients in embryonic chick heart: contributions from Ca2+ channels and the sarcoplasmic reticulum
Authors: Brotto M. A. , Creazzo T. L.
Published: December 2017

In the embryonic mammalian heart, virtually all the Ca2+ available for the Ca2+ transient comes through sarcolemmal Ca2+ influx. However, several studies in avian species indicate that the sarcoplasmic reticulum (SR) is functional relatively early in development. For the present report we studied fura 2 Ca2+ transients elicited by field stimulation in single isolated ventricular myocytes from the day 11 embryonic chick heart to ascertain directly the roles of the SR and Ca2+ channels. A positive staircase phenomenon was observed at higher frequencies of stimulation (1 Hz). Isoproterenol (Iso) increased the peak of the transient in a dose-dependent manner with a maximum increase of 93% in 100 microM Iso. Nifedipine (10 microM) reduced the transient such that is was not observable above background noise. However, Ca2+ transients were visible when the myocytes were stimulated by Iso. These were blocked by approximately 70% with nifedipine, suggesting that most, but not all, of the transient is associated with L-type Ca2+ current. Thus a portion of the transient may result from T-type Ca2+ channels and/or reverse Na+/Ca2+ exchange. Calculations based on integration of the Ca2+ currents and cell volume indicate that as much as one-fourth of the Ca2+ entering via sarcolemmal Ca2+ channels is from T-type channels. Ryanodine at high concentrations (10-100 microM) inhibited the transients by 30%. Both Iso and ryanodine reduced the time to peak, the time constant of the exponential decay, and the total duration of the transients. Depolarizing the myocytes with high KCl induced a large and partially sustained transient when the external solution contained 1.8 mM CaCl2. CaCl2 (10 mM) in the external solution induced large cyclic Ca2+ oscillations. These results suggest that the SR is functional in the embryonic chick heart well before hatching at day 22, although most of the Ca2+ associated with the transient comes through the sarcolemmal Ca2+ channels and possibly reverse Na+/Ca2+ exchange.
PKC-independent inhibition of cardiac L-type Ca2+ channel current by phorbol esters
Authors: Asai T. , Shuba L. M. , Pelzer D. J. , McDonald T. F.
Published: December 2017

Active and inactive phorbol esters were applied to guinea pig ventricular myocytes to study the responses of L-type Ca2+ (ICa,L) and L-type Na+ (INa,L) currents. Phorbol 12-myristate 13-acetate (PMA) (10-100 rM) never stimulated ICa,L or INa,L and frequently depressed them by 5-30% in a voltage-independent manner. However, the phorbol ester consistently activated delayed-rectifying K+ (IK) and Cl- currents. The inhibition of ICa,L occurred approximately 3 times faster than comonitored stimulation of IK, and ICa,L and INa,L were unaffected by two interventions that suppressed IK stimulation [pretreatment with 50 microM 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) and dialysis with pCa 11 versus standard pCa 9 solution]. Inactive phorbol esters 4 alpha-phorbol 12,13-didecanoate (alpha-PDD) and 4 alpha-phorbol had little effect on IK, but alpha-PDD had a PMA-like inhibitory effect on Ca2+ channel currents. We conclude that, unlike the stimulation of IK by PMA, inhibition of Ca2+ channel current by phorbol esters is a protein kinase C-independent action.
Protein tyrosine kinase signaling in cold-stimulated contraction of newborn lamb cerebral arteries
Authors: Wagerle L. C. , Kim S. J. , Russo P.
Published: December 2017

We recently reported a contraction of middle cerebral artery (MCA) preparations isolated from newborn lambs in response to tissue cooling. However, the mechanism(s) by which cold stimulus modifies the contractile properties of MCA is not known. We hypothesize that cold stimulus-triggered contraction may be mediated by a signal transduction pathway associated with protein tyrosine kinase (PTK)-dependent machinery. In the present study the tissue bath technique was used to evaluate the effect of select inhibitors of PTK and protein tyrosine phosphatase (PTP) on the temperature-dependent contractile behavior of isolated MCA from new-born lambs. Reduction of tissue bath temperature from 37 to 21 degrees C stimulated contraction (55 +/- 3% of the response to 120 mM KCl). Two distinct inhibitors of PTK, genistein and tyrphostin 47, completely reversed the cold-stimulated contraction, whereas staurosporine, an inhibitor of protein kinase C, was without effect. Sodium orthovanadate (50 microM) potentiated the cold-stimulated contraction, augmenting the slope of the temperature-force relationship over twofold. Two Ser/Thr phosphatase inhibitors (okadaic acid and calyculin A) had no effect on the temperature-force relationship. These results offer experimental evidence to support a novel hypothesis where PTK/PTP-dependent signal transduction pathways may be preferably targeted by cold stimulus and thus provide a biochemical basis for cold-stimulated modification of cerebral vascular contractile properties.
pH dependence of myosin binding-induced activation of the thin filament in cardiac myocytes and skeletal fibers
Authors: Metzger J. M.
Published: December 2017

The pH dependence of myosin binding-induced thin filament activation was determined in permeabilized cardiac myocytes and slow- and fast-twitch single skeletal muscle fibers by experimental lowering of [MgATP] in the Ca(2+)-free solutions bathing the permeabilized preparations. As the pS (where S is [MgATP] and pS is -log[MgATP]) was increased from 3.0 to 8.0, isometric tension increased to a peak value in the pS range of 4.9-5.3. At pH 7.00, the transition from the relaxed to the activated rigor state was steep in cardiac myocytes [Hill value (nH) = 21.2 +/- 3.1 (SE)] and due to the apparent effect of strongly bound cross bridges to cooperatively activate the thin filament in the absence of added Ca2+. At pH 6.20, the steepness of the tension-pS relationship was markedly reduced (nH = 6.1 +/- 1.0) and the midpoint of the relationship (pS50) was shifted to higher pS values in cardiac myocytes. In comparison, reduced pH had no effect on the steepness or position of the tension-pS relationship in single slow- or fast-twitch skeletal muscle fibers. These findings suggest that myosin binding-induced activation of the thin filament is pH dependent in cardiac myocytes but not in skeletal muscle fibers under these experimental conditions in which Ca2+ is absent.
Modeling [15O]oxygen tracer data for estimating oxygen consumption
Authors: Deussen A. , Bassingthwaighte J. B.
Published: December 2017

The most direct measure of oxidative tissue metabolism is the conversion rate of oxygen to water via mitochondrial respiration. To calculate oxygen consumption from the analysis of tissue residue curves or outflow dilution curves after injection of labeled oxygen one needs realistic mathematical models that account for convection, diffusion, and transformation in the tissue. A linear, three-region, axially distributed model accounts for intravascular convection, penetration of capillary and parenchymal cell barriers (with the use of appropriate binding spaces to account for oxygen binding to hemoglobin and myoglobin), the metabolism to [15O]water in parenchymal cells, and [15O]water transport into the venous effluent. Model solutions fit residue and outflow dilution data obtained in an isolated, red blood cell-perfused rabbit heart preparation and give estimates of the rate of oxygen consumption similar to those obtained experimentally from the flow times the arteriovenous differences in oxygen contents. The proposed application is for the assessment of regional oxidative metabolism in vivo from tissue 15O-residue curves obtained by positron emission tomography.