Rate-limiting steps in the tension development of freeze-glycerinated vascular smooth muscle.

A method for "skinning" arterial smooth muscle is presented which yields isometric tension development typically 60-80% of maximum physiological tension in the presence of micromolar Ca++ and millimolar Mg-ATP, while retaining essentially the native protein content. Using the methods of "CA jump," the time-course of Ca++-activated tension development in the skinned artery can be made identical to, but not faster than, the rate of tension development in the intact artery. In the skinned artery, activating free [Ca++] does not substantially alter the rate at which tension development approaches the final steady tension attained at that free [Ca++] (less than 25% decline in speed for a 10-fold decrease in [Ca++]). These observations are taken to mean that the rate-limiting step in isometric tension development in arterial smooth muscle does not depend directly on Ca++.

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Excitatory pathways in smooth muscle investigated by phase-plot analysis of isometric force development

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1991.261.1.r138 ◽

1991 ◽

Vol 261 (1) ◽

pp. R138-R144

Author(s):

G. A. Van Koeveringe ◽

R. Van Mastrigt

Keyword(s):

Smooth Muscle ◽

Time Constant ◽

Isometric Force ◽

Force Development ◽

Phase Plot ◽

Rate Limiting Step ◽

Limiting Step ◽

Plot Analysis ◽

Excitatory Pathways ◽

Rate Limiting

Excitatory pathways in the smooth muscle of the pig urinary bladder were investigated using phase-plot analysis of isometric contractions. The phase plots, plots of the rate of change of the force as a function of the force itself, were dominated by a straight line described by the horizontal intercept (Fiso) and the vertical intercept (U). The quotient Fiso/U is a time constant that characterizes the rate-limiting step in isometric force development in the muscle. Bladder strips of 1 mm diameter were activated by electrical field stimuli, acetylcholine, potassium, and ATP in combination with selective pathway inhibitors such as verapamil, atropine, or a calcium-free solution containing ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. When pathways that depended significantly on depolarization or intracellular calcium release were selected, the time constant was significantly smaller, indicating a faster process. The results indicated that the rate-limiting step in force development was determined by the influx of extracellular calcium.

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Mechanics of caudal artery relaxation in control and hypertensive rats

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y85-039 ◽

1985 ◽

Vol 63 (3) ◽

pp. 209-213 ◽

Cited By ~ 5

Author(s):

C. S. Packer ◽

N. L. Stephens

Keyword(s):

Smooth Muscle ◽

Time Course ◽

Peripheral Resistance ◽

Loading Conditions ◽

Striated Muscles ◽

Arterial Smooth Muscle ◽

Rate Limiting Step ◽

Caudal Artery ◽

Smooth Muscle Function ◽

Relaxation Curves

Alterations of smooth muscle function can just as easily stem from mechanical alterations in its ability to relax as from alteration in contraction. Since a failure of arterial smooth muscle to relax may contribute to the development of hypertension, we felt it necessary to study the relaxation process in greater depth. The effect of load on the time course of relaxation of rat caudal artery smooth muscle was analyzed either by comparing afterloaded contractions against various loads or by imposing abrupt alterations in load. Unlike mammalian striated muscles in which relaxation was reported sensitive to loading conditions, relaxation in the smooth muscle of the rat caudal artery (n = 17) was found to be largely independent of loading conditions. This type of relaxation has been termed "inactivation-dependent" relaxation; it is typical of muscle tissue in which the calcium sequestering apparatus is poorly developed. Our results suggest that calcium resequestration, or some biochemical process downstream to it, is the rate-limiting step during relaxation in arterial smooth muscle and that this is not qualitatively different for hypertensive arterial smooth muscle. These analytic techniques were used in the study of relaxation of hypertensive vessels. Quantitative analysis of the relaxation curves showed that both isometric and isotonic relaxation time was prolonged in hypertensive arterial smooth muscle. Prolonged isotonic relaxation indicates that hypertensive arteries remain narrowed for prolonged periods compared with normotensive vessels. Such narrowed vessels may be a factor in the increased total peripheral resistance seen in genetic hypertension.

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Force–velocity relationships in hypertensive arterial smooth muscle

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y85-111 ◽

1985 ◽

Vol 63 (6) ◽

pp. 669-674 ◽

Cited By ~ 12

Author(s):

C. S. Packer ◽

N. L. Stephens

Keyword(s):

Smooth Muscle ◽

Spontaneously Hypertensive Rat ◽

Peripheral Resistance ◽

Muscle Length ◽

Maximum Velocity ◽

Isometric Tension ◽

Arterial Smooth Muscle ◽

Tension Development ◽

Force Velocity ◽

Wistar Kyoto

Increased total peripheral resistance is the cardinal haemodynamic disorder in essential hypertension. This could be secondary to alterations in the mechanical properties of vascular smooth muscle. Adequate study has not been made of the force–velocity (F–V) relationship in hypertensive arterial smooth muscle. Increased shortening in arterial smooth muscle would result in greater narrowing of arteries. The objectives of this investigation were to see if there is (i) increased shortening or increased maximum change in muscle length (ΔLmax where L stands for muscle length), (ii) an increased maximum velocity of shortening (Vmax) measured in lo per second where lo is the optimal muscle length for tension development, and (iii) a difference in maximum isometric tension (Po) developed in spontaneously hypertensive rat (SHR; N = 6) compared with normotensive Wistar Kyoto rat (WKY; N = 5) caudal artery strips. An electromagnetic muscle lever was employed in recording force–velocity data. Analysis of these data revealed the following: (a) the SHR mean Po of 6.21 ± 1.01 N/cm2 was not different from the mean WKY Po of 6.97 ± 1.64 N/cm2 (p > 0.05); (b) the SHR preparations showed greater shortening for all loads imposed; (c) the SHR Vmax of 0.016 lo/s was greater than the WKY Vmax of 0.013 lo/s (p < 0.05). This study provides evidence that while hypertensive arterial smooth muscle is not able to produce more force than normotensive arterial smooth muscle, it is capable of faster and greater shortening. The latter could result in increased narrowing of hypertensive arteries and increased blood pressure.

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Time course analysis of the mechanism by which silver inhibits active Na+ and Cl− uptake in gills of rainbow trout

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00448.2003 ◽

2004 ◽

Vol 287 (1) ◽

pp. R234-R242 ◽

Cited By ~ 31

Author(s):

Tammie P. Morgan ◽

Martin Grosell ◽

Kathleen M. Gilmour ◽

Richard C. Playle ◽

Chris M. Wood

Keyword(s):

Rainbow Trout ◽

Carbonic Anhydrase ◽

Time Course ◽

Carbonic Anhydrase Activity ◽

Short Term ◽

Progressive Decline ◽

Rate Limiting Step ◽

Limiting Step ◽

Flow Through ◽

Rate Limiting

A time course analysis using 110mAg, 24Na+, and 36Cl− examined gill silver accumulation and the mechanism by which waterborne silver (4.0 × 10−8 M; 4.3 μg/l) inhibits Na+ and Cl− uptake in gills of freshwater rainbow trout. Analyses of gill and body fluxes allowed calculation of apical uptake and basolateral export rates for silver, Na+, and Cl−. To avoid changes in silver bioavailability, flow-through conditions were used to limit the buildup of organic matter in the exposure water. For both Na+ and Cl− uptake, apical entry, rather than basolateral export, was the rate-limiting step; Na+ and Cl− uptake declined simultaneously and equally initially, with both uptakes reduced by ∼500 nmol·g−1·h−1 over the 1st h of silver exposure. There was a further progressive decline in Na+ uptake until 24 h. Carbonic anhydrase activity was inhibited by 1 h, whereas Na+-K+-ATPase activity was not significantly inhibited until 24 h of exposure. These results indicate that carbonic anhydrase inhibition can explain the early decline in Na+ and Cl− uptake, whereas the later decline is probably related to Na+-K+-ATPase blockade. Contrary to previous reports, gill silver accumulation increased steadily to a plateau. Despite the rapid inhibition of apical Na+ and Cl− uptake, apical silver uptake (and basolateral export) increased until 10 h, before decreasing thereafter. Thus silver did not inhibit its own apical uptake in the short term. These results suggest that reduced silver bioavailability is the mechanism behind the pattern of peak and decline in gill silver accumulation previously reported for static exposures to silver.

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Allosteric Voltage Gating of Potassium Channels I

The Journal of General Physiology ◽

10.1085/jgp.114.2.277 ◽

1999 ◽

Vol 114 (2) ◽

pp. 277-304 ◽

Cited By ~ 193

Author(s):

Frank T. Horrigan ◽

Jianmin Cui ◽

Richard W. Aldrich

Keyword(s):

Time Course ◽

Voltage Dependence ◽

Voltage Gating ◽

K Channel ◽

Exponential Time ◽

Rate Limiting Step ◽

Limiting Step ◽

Voltage Dependent ◽

Rate Limiting ◽

Gating Scheme

Activation of large conductance Ca2+-activated K+ channels is controlled by both cytoplasmic Ca2+ and membrane potential. To study the mechanism of voltage-dependent gating, we examined mSlo Ca2+-activated K+ currents in excised macropatches from Xenopus oocytes in the virtual absence of Ca2+ (<1 nM). In response to a voltage step, IK activates with an exponential time course, following a brief delay. The delay suggests that rapid transitions precede channel opening. The later exponential time course suggests that activation also involves a slower rate-limiting step. However, the time constant of IK relaxation [τ(IK)] exhibits a complex voltage dependence that is inconsistent with models that contain a single rate limiting step. τ(IK) increases weakly with voltage from −500 to −20 mV, with an equivalent charge (z) of only 0.14 e, and displays a stronger voltage dependence from +30 to +140 mV (z = 0.49 e), which then decreases from +180 to +240 mV (z = −0.29 e). Similarly, the steady state GK–V relationship exhibits a maximum voltage dependence (z = 2 e) from 0 to +100 mV, and is weakly voltage dependent (z ≅ 0.4 e) at more negative voltages, where Po = 10−5–10−6. These results can be understood in terms of a gating scheme where a central transition between a closed and an open conformation is allosterically regulated by the state of four independent and identical voltage sensors. In the absence of Ca2+, this allosteric mechanism results in a gating scheme with five closed (C) and five open (O) states, where the majority of the channel's voltage dependence results from rapid C–C and O–O transitions, whereas the C–O transitions are rate limiting and weakly voltage dependent. These conclusions not only provide a framework for interpreting studies of large conductance Ca2+-activated K+ channel voltage gating, but also have important implications for understanding the mechanism of Ca2+ sensitivity.

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Solid products and rate-limiting step in the thermal half decomposition of natural dolomite in a CO2(g) atmosphere

Thermochimica Acta ◽

10.1016/s0040-6031(02)00603-2 ◽

2003 ◽

Cited By ~ 1

Author(s):

D Beruto

Keyword(s):

Rate Limiting Step ◽

Limiting Step ◽

Rate Limiting

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Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

Thrombosis and Haemostasis ◽

10.1055/s-0038-1646709 ◽

1978 ◽

Vol 39 (02) ◽

pp. 496-503 ◽

Cited By ~ 8

Author(s):

P A D’Amore ◽

H B Hechtman ◽

D Shepro

Keyword(s):

Endothelial Cells ◽

Ornithine Decarboxylase ◽

Decarboxylase Activity ◽

Aortic Endothelial Cells ◽

Ornithine Decarboxylase Activity ◽

Rate Limiting Step ◽

Bovine Aortic Endothelial Cells ◽

Limiting Step ◽

Rate Limiting ◽

Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

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