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P Hellstrand

Publications and source records attributed to P Hellstrand.

At least 37 records · Page 2Linked to original sources
PubMed1995

Polyamines inhibit myosin phosphatase and increase LC20 phosphorylation and force in smooth muscle.

The increase in Ca(2+)-activated force caused by polyamines in beta-escin-permeabilized guinda pig ileum is shown to be associated with increased myosin 20-kDa light chain (LC20) phosphorylation and shortening velocity. Myosin LC20 dephosphorylation with arrested kinase activity was slower in the presence of 1 mM spermine. Smooth muscle phosphatases (SMP-I, -II, -III, and -IV) isolated from turkey gizzard are all active against phosphorylated LC20, but only SMP-III and -IV dephosphorylate heavy meromyosin (HMM). Spermine inhibited SMP-III activity toward LC20 but stimulated HMM dephosphorylation, whereas SMP-IV was inhibited with both substrates. In contrast, SMP-I and -II were stimulated by spermine. The relative effects of different polyamines correlated with an increasing number of positive charges. Spermine did not affect binding of SMP-IV to myosin and did not dissociate any of the subunits of the enzyme. Incubation of permeabilized strips with SMP-IV resulted in attenuated responses to Ca2+, an effect that was opposed by spermine and abolished by microcystin-LR. We conclude that spermine selectively inhibits myosin phosphatase activity and suggest that polyamines function as endogenous myosin phosphatase inhibitors.

Animals↗
PubMed1994

Cross-bridge kinetics and shortening in smooth muscle.

Stiffness measurements were performed on smooth muscle preparations from guinea-pig taenia coli to obtain information on the number of attached cross bridges under varying contractile conditions. The normalized stiffness of the cross-bridge system in smooth muscle may be of a magnitude similar to that assumed in skeletal muscle. Transition from isometric contraction to unloaded shortening was associated with a decrease in stiffness to 50% or less of the isometric value, slightly higher than that found in skeletal muscle fibers. Comparison of phasic (5 s) and tonic (5 min) contractions showed lower Vmax, intracellular [Ca2+], and myosin 20 kDa light chain phosphorylation at 5 min, indicating development of a latch state. Isometric force and stiffness were identical in the two types of contraction. However, stiffness during unloaded shortening was greater in the latch state, which may be the result of the presence of a population of cross bridges with a low rate constant for detachment.

Animals↗
PubMed1994

Polyamines increase Ca2+ sensitivity in permeabilized smooth muscle of guinea pig ileum.

The effects of polyamines were investigated in strips of smooth muscle from guinea pig ileum permeabilized with beta-escin (0.005%). Spermine (1 mM) inhibited transient contractions induced in Ca(2+)-free medium by carbachol (0.1 mM) and GTP gamma S (0.1 mM) but potentiated responses to caffeine (20 mM) and D-myo-inositol 1,4,5-trisphosphate (40 microM). At high ethylene glycol-bis(beta-amino-ethyl ether)-N,N,N',N'-tetraacetic acid concentration (10 mM) and in the presence of A-23187 (10 microM), force at optimal and suboptimal Ca2+ concentrations was increased both by spermine and by carbachol. Spermine did not potentiate contraction in Ca(2+)-free medium or after full thiophosphorylation of the regulatory 20-kDa myosin light chains but slightly potentiated contractions produced by partial thiophosphorylation. Also, spermidine and putrescine, as well as the aminoglycoside antibiotic neomycin, increased sensitivity to Ca2+, with potency correlating with number of positive charges. After permeabilization by a high concentration (0.1%) of beta-escin, the sensitivity to Ca2+ was increased by spermine but not by GTP gamma S. In preparations permeabilized by Triton X-100, spermine slightly increased Ca2+ sensitivity but not maximal force. Tissue contents of putrescine, spermidine, and spermine in intact ileum muscle were 8, 98, and 184 nmol/g, respectively. Permeabilization by 0.005 and 0.1% beta-escin reduced spermine contents by 40 and 53%, respectively. Effects of added polyamines in permeabilized preparations may thus reflect physiological effects of endogenous polyamines modulating contraction in the intact tissue.

Animals↗
PubMed1993

Improvement in i.v. regional anaesthesia by re-exsanguination before surgery.

A modification of an i.v. regional anaesthesia (IVRA) technique is described in which the arm is re-exsanguinated before surgery (re-IVRA). IVRA and re-IVRA were compared for quality of operative field, sensory and motor block, quality of analgesia and blood concentrations of prilocaine, lignocaine and mepivacaine in a double-blind study in 120 patients undergoing hand surgery. Re-IVRA provided a significantly better surgical field without affecting sensory or motor block. Re-exsanguination improved tolerance of the tourniquet. Plasma concentrations in the re-IVRA group showed some increases, but these were not in the toxic range.

Adolescent↗
PubMed1993

Effects of polyamines on intracellular calcium and mechanical activity in smooth muscle of guinea-pig taenia coli.

The effects of the polyamines putrescine, spermidine and spermine on the mechanical activity in smooth muscle from guinea-pig taenia coli were investigated. Tissue concentrations of spermidine and spermine were about 240 and 160 nmol g-1, respectively, while the putrescine concentration was much lower (4 nmol g-1). Intracellular [Ca2+] was determined using the Fura-2 method and the effects of extracellularly applied polyamines were observed. Spermine (10(-5)-10(-3) mol l-1) dose-dependently inhibited spontaneous contractions as well as contractions induced by 20-25 mmol l-1 KCl, with 10(-3) mol l-1 spermine giving nearly total relaxation. Spermidine (10(-3) mol l-1) relaxed a 20 mmol l-1 KCl contracture, while putrescine had no effect. A decrease in intracellular [Ca2+] accompanied the relaxation induced by spermine. In contrast to the effects on spontaneous activity and intermediate [KCl], both the contraction and the accompanying increase in intracellular [Ca2+] induced by 90-120 mmol l-1 KCl were unaffected by spermine. Spermine did not affect the maximal Ca(2+)-induced force of chemically skinned taenia coli preparations, but a small potentiating effect on the Ca2+ sensitivity was observed. The results indicate that the relaxation induced by spermine depends on an intact cell membrane. Furthermore, the relaxing effect is due to decreased intracellular [Ca2+] and seems to occur only when the contraction is elicited by repetitive action potentials, and not by sustained depolarization.

Action Potentials↗
PubMed1993

Effects of metabolic inhibition on cytoplasmic calcium and contraction in smooth muscle of rat portal vein.

Contractions in the rat portal vein, evoked by spontaneous action potentials or depolarizing high-K+ solution, are rapidly and reversibly inhibited by hypoxia or respiratory blockade. Intracellular free calcium ([Ca2+]i) was measured using Fura-2 to evaluate the effects of metabolic blockade on excitation-contraction coupling. Spontaneous contractions were associated with transient increases in [Ca2+]i. During exposure to cyanide (0.2-0.4 mM) or 2,4-dinitrophenol (30 microM) the duration and amplitude of the Ca2+ transients were decreased, leading to a decreased mean time integral of the individual [Ca2+]i transient, and corresponding decrease in the duration and amplitude of the contraction. Basal [Ca2+]i was increased in the presence of the metabolic inhibitors. High-K+ (40 mM) contractions caused a sustained increase in [Ca2+]i, which was not inhibited by exposure to cyanide, although the amplitude of the associated contraction was greatly reduced. Together with the earlier demonstration of decreased 20 kD myosin light chain phosphorylation under these conditions, this indicates that the activation of contraction is influenced by metabolism via the energy dependence of the light chain phosphorylation reaction. Thus at least three steps in the excitation-contraction sequence are influenced by inhibition of oxidative metabolism: membrane excitation, light chain phosphorylation, and the cross-bridge cycle. This provides mechanisms for a high degree of metabolic sensitivity of vascular tone, of importance for the adaptation of blood flow to tissue metabolic demands.

Action Potentials↗
PubMed1993

Cross-bridge kinetics during shortening in early and sustained contraction of intestinal smooth muscle.

Mechanisms responsible for the decrease in shortening velocity after prolonged contraction ("latch" state) were investigated at identical force during early (20 s, "phasic") and sustained (5 min, "tonic") phases of high-K+ (25-30 mM) contractions in smooth muscle of guinea pig taenia coli. Cytoplasmic Ca2+ concentration, myosin light-chain phosphorylation, and maximum shortening velocity all declined from 20 s to 5 min of contraction. The time course of shortening following isotonic quick release was biexponential, with a fastest rate constant of approximately 80 s-1 in both phasic and tonic contractions. Stiffness was identical in phasic and tonic contraction; however, after a release to slack length and unloaded shortening, stiffness during restretch was greater in tonic contraction (51 vs. 43% of isometric stiffness after 16 ms of unloaded shortening). Stiffness decreased after release with a rate constant of approximately 200 s-1, slightly greater in phasic than in tonic contraction. The results indicate that the number of attached cross bridges during unloaded shortening, while substantially reduced relative to the isometric value, is higher in latch than in nonlatch, consistent with a lower detachment relative to attachment rate.

Animals↗
PubMed1992

Paradoxical decrease in cytosolic calcium with increasing depolarization by potassium in guinea-pig mesotubarium smooth muscle.

The free intracellular Ca2+ concentration ([Ca2+]i) was measured simultaneously with isometric force in strips of guinea-pig mesotubarium using the Fura-2 technique. [Ca2+]i and force were maximal at a relatively low (30 mM) concentration of extracellular K+ ([K+]o), and declined at 90 and 140 mM K+. Plateau values of both [Ca2+]i and force were higher in the presence of 5.10(-6) M ryanodine, indicating that the sarcoplasmic reticulum (SR) contributes to the decline with depolarization. Force and [Ca2+]i at 90 mM K+ were both lower then the high-K+ solution was applied after a period in 30 mM K+ than after a period in normal solution (5.9 mM K+), consistent with inactivation of Ca2+ channels during prolonged depolarization. Addition of carbachol to the depolarized muscle caused a maintained increase in force without maintained increase in [Ca2+]i. We conclude that the decrease in force at increased [K+]o (the "calcium-potassium paradox") is due to a membrane-potential-mediated decrease in [Ca2+]i and, to a lesser extent, to desensitization of the contractile-regulatory apparatus to Ca2+.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Metabolic correlates to pacemaker activity in the smooth muscle of guinea-pig mesotubarium.

Oxygen consumption (FO2) and lactate production (Flac) were measured during spontaneous activity in the guinea-pig mesotubarium. During spontaneous contractions FO2 increased to maximally 0.270 +/- 0.025 mumol min-1g-1 (n = 23), followed by a rapid fall immediately upon relaxation. In the relaxed period (5-15 min) between spontaneous contractions FO2 continued to slowly decrease by about 25% towards a final value of 0.150 +/- 0.01 mumol min-1g-1. Flac showed no consistent variation during the relaxed period. Ouabain (10(-6)M) produced a contracture, which was abolished by the Ca2(+)-antagonist felodipine (10(-6)M). In the presence of felodipine, addition of ouabain caused depolarization and a decrease of oxygen consumption by 21% and of lactate production by 31%. Exchange of glucose in the physiological Krebs solution for beta-hydroxybutyrate did not influence spontaneous activity, while subsequent addition of cyanide (2 mM) abolished contractions and caused a hyperpolarization of 15 mV. Blockade of ATP-dependent K+ channels by addition of glibenclamide (10(-7)M) to the relaxed muscle in this situation caused spontaneous contractile activity to reappear. In glucose-containing Krebs solution glibenclamide had no effect on the spontaneous contractile and electrical activity and contractions persisted after addition of cyanide. The relaxing and hyperpolarizing effect of pinacidil could be counteracted by addition of glibenclamide. The results suggest that a decrease in electrogenic Na+/K(+)-pump activity in the course of the relaxed period between contractions could contribute to the pacemaker behaviour. ATP-dependent K+ channels, while having little influence on the spontaneous contractile activity under normal metabolic conditions, could be activated during blockade of aerobic and anaerobic metabolism, leading to inhibition of pacemaker activity.

Adenosine Triphosphate↗
PubMed1991

Heat production in chemically skinned smooth muscle of guinea-pig taenia coli.

1. The rate of heat production of chemically skinned guinea-pig taenia coli smooth muscle at 25 degrees C was measured using microcalorimetric techniques. 2. Muscle strips were mounted isometrically and incubated in solutions containing MgATP (3.2 mM) and phosphocreatine (PCr, 12 mM), pH 6.9. Activation was obtained by the injection of Ca2+ into the sample compartment of the calorimeter. 3. The heat production rate of the resting preparation (pCa 9) was 0.40 +/- 0.03 mW g-1 wet weight (n = 23). During maximal activation (pCa 4.8) the heat rate increased to 1.12 +/- 0.07 mW g-1 (mean +/- S.E.M., n = 15). With stepwise increase in [Ca2+] from pCa 9 to 4.8 the energetic cost of force maintenance tended to increase at higher [Ca2+]. 4. After activation by Ca2+, the heat production rate reached its maximum while force was still increasing. 5. Changing ionic strength from 90 to 150 mM had no effect on either basal or activated heat rate. Oligomycin, amphotericin B and the adenylate kinase inhibitor Ap5A had no effect on the basal heat rate. 6. Exchanging ATP in the incubation medium for inosine triphosphate (ITP) reduced the force and heat production after injection of Ca2+. The basal heat production was not lowered when ATP was exchanged for ITP. 7. The observed enthalpy change for PCr splitting at 25 degrees C (pH 6.9, ionic strength 90 mM) was -28 +/- 3 kJ mol-1 (mean +/- S.E.M., n = 9). After correction for the phosphate equilibrium, buffer reactions, and Mg2+ binding to PCr and HPO42-, the net enthalpy change is calculated to be -39 +/- 3 kJ mol-1. 8. Heat production in the skinned smooth muscle consists of one basal component present in relaxed muscle, and one component associated with contraction. The nature of the basal heat production is unclear but does not seem to involve turnover of phosphate on the myosin light chains. The increase in the energetic tension cost with increasing activation by Ca2+ has implications for the understanding of the contractile mechanism in smooth muscle.

Animals↗
PubMed1991

Force response to rapid length change during contraction and rigor in skinned smooth muscle of guinea-pig taenia coli.

1. Mechanical transients in fibre bundles of skinned smooth muscle of guinea-pig taenia coli at 21-22 degrees C were investigated by recording tension responses to length changes of up to 9%, complete within 0.3 ms. 2. The length-force relationship, recorded continuously during rapid stretch of a Ca(2+)-activated contracted muscle, was linear up to at least 2.5 times the isometric force, corresponding to a stretch of about 1%. The slope of the relationship (stiffness) increased with the velocity of stretch. 3. During rapid release (about 120 muscle lengths s-1) the length-force relationship was linear down to about 50% of the initial isometric force, reached at about 80 microseconds after the beginning of the release. At lower force the length-force relationship was concave upwards. The linear portion extrapolated to zero force at about -0.008 muscle lengths. In large releases the length-force plot approached the force baseline under an acute angle, and negative force was transiently exerted. 4. When the muscle was stretched back to the initial length after a shortening step, force transiently rose above the isometric force, but decayed back within a few milliseconds. Stiffness at the time of restretch was compared with that in the initial shortening step by plotting force vs. length, and was found to be decreased to 63% within 0.3 ms of a step to zero force. Stiffness decreased further with time at zero force, and after 256 ms was about 29% of the isometric value. 5. In rigor, caused by the introduction of ATP-free solution during the plateau of isometric contraction, fibre tension decreased to about 30% of the active tension, whereas stiffness relative to force increased; 82% of the initial stiffness in rigor was detected in a restretch immediately after a shortening step, decreasing to 59% at 256 ms. When the fibre was activated at suboptimal [Ca2+] to cause the same force as in rigor, stiffness was lower than in rigor and decreased more after a release. 6. After completion of a release-stretch cycle, stiffness was rapidly restored to the same value as in isometric contraction. Test stretches at different points in time after completion of the cycle revealed that most of the stiffness had been restored within 1 ms of the restretch, occurring concomitantly with a decay in force.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Free cytosolic calcium during spontaneous contractions in smooth muscle of the guinea-pig mesotubarium.

The free intracellular calcium ion concentration ([Ca2+]i) was measured simultaneously with isometric force in strips of guinea-pig mesotubarium using the Fura-2 technique. During the relaxed period (5-15 min) between spontaneous contractions [Ca2+]i continues to decrease after full mechanical relaxation to reach a minimal level of 86 +/- 8 nM (n = 9) just before the start of the next contraction. During the spontaneous contractions (5-15 min) [Ca2+]i reached a maximum of 211 +/- 19 nM and then oscillated between 155 +/- 16 nM and 194 +/- 9 nM. Increased extracellular Ca2+ concentration to 10 mM from the standard concentration of 1.5 mM caused a decreased frequency of spontaneous contractions and an increase in [Ca2+]i both in the relaxed and contracted states. In 10 mM extracellular Ca2+, addition of AlF4-, as 1 mM NaF + 10 microM AlCl3, caused a sustained increase in [Ca2+]i and maintained force. Addition of verapamil (10 microM) in this situation decreased [Ca2+]i to the resting level. The results suggest that the cyclic appearance of trains of action potentials is related to variation in [Ca2+]i, possibly via inactivation of Ca2(+)-dependent K+ channels.

Action Potentials↗
PubMed1990

Effects of extracellular K+ and Ca2+ on membrane potential, contraction and 86Rb+ efflux in guinea-pig mesotubarium.

The effects of varying extracellular concentrations of K+ and Ca2+ [K+]o and [Ca2+]o on force development and membrane potential were investigated in the guinea-pig mesotubarium. At [K+]o up to 40 mM, spontaneous action potentials were present, while higher [K+]o gave sustained contractures at a stable membrane potential (-24 to -12 mV for [K+]o from 60 to 120 mM). Tension decreased successively with increasing [K+]o from 30 to 120 mM. The relaxing potency of the dihydropyridine Ca2+ antagonist, felodipine, increased as the membrane was depolarized with increasing [K+]o and action potentials ceased. These results are compatible with the existence of Ca2+ channels showing voltage-dependent affinity with dihydrophyridines. Increasing [Ca2+]o from 2.5 to 10 mM caused membrane hyperpolarization by about 11 mV and was accompanied by a lower frequency of spontaneous contractions and a longer duration of the relaxation between contractions. 86Rb+ efflux measurements in 60 mM K+ in the absence and presence of felodipine revealed a Ca2(+)-dependent component of the voltage-activated efflux. In normal solution (5.9 mM K+), efflux in the presence of felodipine was similar to the minimal value during normal spontaneous activity. The results indicate regulation of the permeability of K+ channels by the intracellular Ca2+ concentration ([Ca2+]i) and suggest participation of such channels in the generation of the regularly occurring bursts of action potentials characteristic of spontaneous activity in the mesotubarium.

Animals↗
PubMed1989

Calcium sensitivity and energetics of contraction in skinned smooth muscle of the guinea pig taenia coli at altered pH.

Calcium-sensitivity of contraction, force-velocity relation and ATP hydrolysis rate at different pH (6.2-7.8) were investigated in skinned smooth muscle preparations from the guinea pig taenia coli. Varied free-calcium levels were buffered by 4 mM BAPTA (1,2-bis(2-aminophenoxy)-ethane-N,N,N'N'-tetraacetic acid) which has calcium binding properties little affected by pH. A small increase of calcium-sensitivity of contraction was seen at pH 6.2 compared to 6.9 and 7.8 (ED50 shift of about 0.15 pCa units). The isometric force and Vmax in fibres activated either by calcium or by thiophosphorylation of the myosin light chains were each reduced by about 15% at pH 6.2 compared to 6.9 and 7.8. Following an isotonic quick release the shortening velocity decreases with time. This effect was more pronounced at pH 6.2 than at pH 6.9 or 7.8. The ATP hydrolysis rates in relaxed and thiophosphorylated fibres were essentially unaffected by alteration in pH between 6.2 and 7.8. Due to the lower force, energetic cost of force maintenance was thus somewhat increased at pH 6.2. These results suggest that pH alteration between 6.2 and 7.8 have effects on the properties of the contractile machinery of the smooth muscle in the skinned guinea pig taenia coli. The effects are however small and therefore probably of little functional importance over a pH range which should cover most cases of intracellular pH alteration under physiological or pathophysiological conditions.

Adenosine Triphosphate↗
PubMed1989

Effects of reduced oxygen tension on endothelium-dependent relaxation induced by acetylcholine differ in rabbit femoral artery and jugular vein.

In intact rabbit femoral artery rings pre-contracted with phenylephrine, acetylcholine (ACh; 10(-9)-10(-6) M) produces endothelium-dependent relaxation, abolished after mechanical rubbing to remove the endothelium. The response to ACh was absent at low oxygen tension (less than or equal to 4 kPa) or in the presence of sodium cyanide (1 mM). Intact rabbit jugular veins relaxed to ACh in lower concentration than did the femoral artery, 10(-10)-10(-8) M; at sufficient ACh concentration the relaxation was complete. In veins with completely removed endothelium no relaxation to ACh occurred, and at concentrations above 3 x 10(-7) M the response was a contraction. The relaxation response to ACh of intact veins persisted during contraction at lower oxygen tension or in the presence of 1 mM sodium cyanide. In rubbed veins, cyanide consistently induced a transient contraction, which was absent in intact veins. The study demonstrates pronounced endothelium-dependent relaxation to ACh in a venous preparation, with a markedly lower sensitivity of the relaxation response to hypoxia than in a muscular artery of the same species.

Acetylcholine↗
PubMed1989

Shortening velocity, myosin light chain phosphorylation and Ca2+ dependence of force during metabolic inhibition in smooth muscle of rat portal vein.

The concentration-response relation for Ca2+ (0.2-5.0 mM) of high-K+ contractures (40 mM) in the rat portal vein during respiratory inhibition by 0.2 mM cyanide was investigated. A reduction of force in the presence of cyanide to about 30% of control was associated with a leftward shift of the normalized concentration-response relation. When force at the plateau of high-K+ contractures (at about 2 min) was reduced to 65 +/- 2% due to the addition of cyanide, the maximal shortening velocity (Vmax) was 94 +/- 5% of control (n = 6). In electrically (AC) stimulated preparations giving short tetanic contractions, a reduction of active force to 58 +/- 2% of control in the presence of cyanide was associated with a reduction of Vmax to 83 +/- 5% (n = 7). Phosphorylation of the 20-kDa regulatory light chains (LC20) of the myosin molecule was studied in the relaxed state and at the plateau of high-K+ contractures for comparison with the mechanical data. Both control and cyanide-treated preparations showed 9% LC20 phosphorylation in nominally Ca2+-free solution (n = 6). After activation the level of phosphorylation increased to 30 +/- 3% (n = 9) in the control veins. In cyanide-treated veins, where force was reduced to 42 +/- 6% compared to a preceding control period, the phosphorylation level was 17 +/- 2% (n = 7). The study suggests that the mechanical changes caused by inhibition of cellular respiration may involve the combined effect of several metabolic alterations, including decreased LC20 phosphorylation during contraction, but apparently not decreased intracellular Ca2+ concentration or sensitivity of the contractile system to Ca2+.

Animals↗