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Biomedical subjects

R Casteels

Publications and source records attributed to R Casteels.

At least 163 records · Page 9Linked to original sources
PubMed1982

Demonstration of the phosphorylated intermediates of the Ca2+-transport ATPase in a microsomal fraction and in a (Ca2+ + Mg2+)-ATPase purified from smooth muscle by means of calmodulin affinity chromatography.

Ca2+ -dependent hydroxylamine-sensitive phosphorylated proteins can be demonstrated in a microsomal fraction of porcine antrum (stomach) smooth muscle and in a Ca2+ -transport ATPase ((Ca2+ + Mg2+)-ATPase) purified from this tissue by means of a calmodulin affinity technique. These phosphoproteins represent the phosphorylated intermediates of the (Ca2+ + Mg2+)-ATPases. In the (Ca2+ + Mg2+)-ATPase purified from smooth muscle the phosphorylated intermediate has an Mr of 130000 corresponding to the value found for erythrocyte (Ca2+ + Mg2+)-ATPase. In the smooth muscle microsomal fraction this 130 kDa phosphoprotein can also be seen, although its intensity is usually very low compared to a corresponding phosphorylation at Mr 100000. Including La3+ together with Ca2+ during phosphorylation of the microsomes increased selectively the steady state-level of the 130 kDa phosphoprotein over the value of the 100 kDa one. The 100 kDa Ca2+ -dependent phosphoprotein could either indicate the presence of a (Ca2+ + Mg2+)-ATPase of the same type of sarcoplasmic reticulum of skeletal muscle, or it could represent a proteolytic product of the 130 kDa phosphoprotein.

Animals↗
PubMed1982

Effect of isoprenaline on intracellular Ca uptake and on Ca influx in arterial smooth muscle.

We have investigated the effect of isoprenaline on the amplitude of the transient contraction of isolated arteries induced by releasing the intracellular Ca with an agonist during incubation in a Ca-free solution. Under some conditions this force development is an indication of the amount of Ca in the intracellular store. Loading the store in high K+ solution in the presence of isoprenaline increases the amplitude of the subsequent contraction in Ca-free solution by 6 to 16% as compared to the control. The presence of isoprenaline during the loading procedure in the control solution with 5.9 mM K+ does not affect the amplitude of the subsequent contraction of the rabbit ear artery. In the rabbit coronary artery such pretreatment with isoprenaline inhibits the contraction to 40% of the control. These results indicate that beta-agonists may stimulate the Ca uptake in the intracellular store and, depending on the tissue, inhibit the influx of Ca.

Animals↗
PubMed1982

Membrane potential and excitation-contraction coupling in smooth muscle.

To describe the role of the membrane potential in the regulation of the excitation-contraction coupling of smooth muscle, two types of smooth muscle tissues, the tenia coli of the guinea pig and the ear artery of the rabbit, have been compared. The first tissue provides an example of electromechanical coupling, and the second one is characterized by pharmacomechanical coupling. Under physiologic conditions tenia coli present action potentials accompanied by an entry of Ca2+ into the cells. However, the calculated amount of Ca entering during an action potential is, according to several authors, insufficient to cause contraction. An alternative mechanism to increase the intracellular Ca2+ could be a Ca-induced or depolarization-induced Ca release. Application of acetylcholine increases the ion permeability of the plasma membrane, thereby causing an increase of the spike frequency and a membrane depolarization. In addition, it induces a release of cellular Ca. However, the changes of the membrane potential seem to be the primary regulatory factor in determining the activity of this tissue. In the ear artery the role of the membrane potential seems to be much less important than in tenia coli. There is no electrical activity, and norepinephrine induces a force development without depolarizing the cells. This agonist causes a release of Ca from an intracellular store and at the same time increases the Ca permeability of the membrane. We have obtained experimental evidence suggesting that norepinephrine could act primarily on a cellular Ca store close to the cell membrane. A depletion of this store could result in a rapid flow of external Ca into this store and from there into the cytoplasm. The receptor-operated channels would be incorporated in the plasma membrane-sarcoplasmic reticulum junction.

Acetylcholine↗
PubMed1981

Partial purification of (Ca2+ + Mg2+)-dependent ATPase from pig smooth muscle and reconstitution of an ATP-dependent Ca2+-transport system.

(CaMg)ATPase [(Ca2+ + Mg2+)-dependent ATPase] was partially purified from a microsomal fraction of the smooth muscle of the pig stomach (antrum). Membranes were solubilized with deoxycholate, followed by removal of the detergent by dialysis. The purified (CaMg)ATPase has a specific activity (at 37 degrees C) of 157 +/- 12.1 (7)nmol.min-1.mg-1 of protein, and it is stimulated by calmodulin to 255 +/- 20.9 (7)nmol.min.mg-1. This purification of the (CaMg)ATPase resulted in an increase of the specific activity by approx. 18-fold and in a recovery of the total enzyme activity of 55% compared with the microsomal fraction. The partially purified (CaMg)ATPase still contains some Mg2+-and (Na+ + K+)-dependent ATPase activities, but their specific activities are increased relatively less than that of the (CaMg)ATPase. The ratios of the (CaMg)ATPase to Mg2+- and (Na+ + K+)-dependent ATPase activities increase from respectively 0.14 and 0.81 in the crude microsomal fraction to 1.39 and 9.07 in the purified preparation. During removal of the deoxycholate by dialysis, vesicles were reconstituted which were capable of ATP-dependent Ca2+ transport.

Adenosine Triphosphate↗
PubMed1981

Tension response and 45Ca release in vascular smooth muscle incubated in Ca-free solution.

The contractile response of arterial smooth muscles induced by agonists as noradrenaline or histamine in Ca-free solution consists of two phases: an initial phasic component, which is transient and accompanied by a release of cellular Ca, and a small tonic component, which persists as long as the agonist is present. A second admission of the agonist without reexposure to Ca elicits only the tonic component. This tonic contraction differs in several respects from the phasic response obtained in Ca-free solution: it is independent of the duration of exposure to the Ca-free solution, it can be elicited many times without reexposure to Ca, and it is not accompanied by a measurable release of Ca from the cells. During superfusion with Ca-free solution, a tonic contraction is also induced by fluoride ions at concentrations exceeding 4 mM. The amplitude of this contraction is maximal at about 12 mM. Increasing the fluoride concentration shortens the delay between the addition of the F-- and the onset of the contraction. As is the case for the tonic noradrenaline-response, the F--induced contractions can be elicited many times without reexposure to Ca. The tonic contractions evoked by noradrenaline or histamine and by fluoride ions are additive. Both contractions are reversibly inhibited by caffeine, theophylline, Na-nitroprusside, papaverine and by nitroglycerine. The possibility that these tonic contractions are not accompanied by an increase of the cytoplasmic Ca2+ concentration is discussed.

Animals↗
PubMed1981

Temperature-dependence of 45Ca fluxes and contraction in vascular smooth muscle cells of rabbit ear artery.

The effect of cooling from 35 to 20 degrees C on the 45Ca-exchange and on the contractile response of rabbit ear artery has been investigated. The amplitude of the contraction induced by K-depolarization at 20 degrees C is reduced to about 60% of its value at 35 degrees C, whereas the response to noradrenaline is not significantly affected. Cooling induces a 2 to 4-fold reduction of the 45Ca-efflux rate. This effect also occurs in Ca-free medium and in solutions containing 1 mM La. It also occurs in Na-free medium and in tissues in which the transmembrane Na-gradient has been reduced. At 20 degrees C, the 45Ca-influx in unstimulated tissues and in K-depolarized preparations is significantly lower than at 35 degrees C. In Ca-depleted tissues, i.e. tissues in which the noradrenaline-sensitive Ca-store has been emptied by a stimulation with the agonist in Ca-free solution, the 45Ca-influx is not significantly affected by cooling. The gradual depletion of the noradrenaline-sensitive Ca-store in Ca-free solutions is at 20 degrees C much slower than at 35 degrees C. The amount of Ca released by noradrenaline is not affected by cooling, whereas for the same amount of Ca released the contractile response is higher at 20 degrees C. These findings indicate that temperature affects the transmembrane Ca-extrusion and the Ca-influx through voltage-dependent channels. The properties of the noradrenaline-sensitive Ca-store are less sensitive to temperature.

Animals↗
PubMed1981

Exchange characteristics of the noradrenaline-sensitive calcium store in vascular smooth muscle cells or rabbit ear artery.

1. The amplitude of the noradrenaline-sensitive Ca stores has been estimated by measuring the amplitude of the transient contraction induced by the agonist in Ca-free solution. or by measuring the amount of 45Ca released under these conditions. 2. The rate of filling of this store after depletion is much faster than the rate of depletion in Ca-free solution, and depends on [Ca]o in the bathing solution. The degree of filling also depends on [Ca]o. 3. At the same [Ca]o the degree of filling is higher in K-depolarized tissues than in control tissues. However at 10 mM-[Ca]o and 5.9 mM-K the amount of Ca taken up by the store is larger than that after loading in 0.2 mM-Ca and 141.4 mM-K, although the tissues remain relaxed during loading at 5.9 mM-K and contracted at 141.4 mM-K. 4. The Ca antagonists D600 and nicardipine selectively block the contraction induced by K depolarization, but do not affect appreciably the noradrenaline-induced contraction. 5. The filling of the store is not significantly reduced by the presence of the Ca antagonists in solutions containing 5.9 mM-K. However these antagonists reduce the degree of filling in K-rich loading solution to a level which is lower than that observed in the control. 6. Mn blocks both the contraction induced by K-rich solution and the tonic component of the noradrenaline-induced contraction and its also inhibits filling of the store. 7. The results suggest that the filling of the store under physiological conditions occurs by a direct pathway between the store and the extracellular medium.

Animals↗
PubMed1980

The effect of calmodulin on the active calcium-ion transport and (Ca2+ + Mg2+)-dependent ATPase in microsomal fractions of smooth muscle compared with that in erythrocytes and cardiac muscle.

The Ca2+ uptake and the (Ca2+ + Mg2+)-dependent ATPase of the porcine coronary-artery smooth-muscle microsomal fraction ('microsomes') are only slightly stimulated by calmodulin. The Ca2+ uptake after 2 min in the absence of oxalate, corrected for the ATP-independent binding, increased by a factor of 1.44, whereas the (Ca2+ + Mg2+)-dependent ATPase is stimulated 1.39 times. These findings contrast with the effect observed in human erythrocyte 'inside-out' microsomes. In these vesicles calmodulin increases the Ca2+ uptake after 20 min in an oxalate-free medium and the (Ca2+ + Mg2+)-dependent ATPase respectively by a factor of 3.82 and 6.18. The magnitude of the calmodulin stimulation of the Ca2+ transport in coronary-artery microsomes is similar to that observed in heart microsomes.

Animals↗
PubMed1980

Demonstration of a (Ca2+ + Mg2+)-ATPase activity probably related to Ca2+ transport in the microsomal fraction of porcine coronary artery smooth muscle.

A (Ca2+ + Mg2+)-ATPase activity is demonstrated in the microsomal fraction of porcine coronary artery. The characteristics of the ATPase activity are compared with those of the Ca2+ transport, both measured in similar solutions. It is concluded that the (Ca2+ + Mg2+)-ATPase is related to the Ca2+ transport because: 1. Both transport and ATPase have similar low Km values for Ca2+ as well as comparable Hill coefficients. The Km values are respectively 0.34 +/- 0.03 microM [4] and 1.17 +/- 0.15 microM [6]. The Hill coefficients are n = 1.69 +/- 0.09 [4] and n = 1.23 +/- 0.17 [6]. 2. Ionophores A23187 and X537A stimulate (Ca2+ + Mg2+)-ATPase activity while they inhibit net Ca2+ accumulation by increasing the Ca2+ permeability of the membranes. 3. The V values for Ca2+ accumulation and for (Ca2+ + Mg2+)-ATPase are comparable.

Animals↗
PubMed1980

The effect of histamine on the smooth muscle cells of the ear artery of the rabbit.

Histamine activates both H1- and H2-receptors in the ear artery of the rabbit. The specific action of these receptor activations on the membrane potential and the force development has been investigated by using the H1-blocking agent mepyramine and the H2-blocking agent cimetidine. H1-activation depolarizes and increases force development, while H2-activation hyperpolarizes and reduces force development. These effects on the force development can occur independently of the changes of the membrane potential. By determining the effect of histamine on tissues which were denervated with 6-hydroxydopamine it was shown that histamine exerts its effect directly on the smooth muscle cells. Na-deficiency depolarizes the smooth muscle cells, but it also reduces the changes of the membrane potential and the force development induced by H1-stimulation. K-free medium prevents the hyperpolarizing effect of H2-activation. As far as the ion fluxes are concerned an H1-activation is found to induce an increased efflux of K while a simultaneous H2-activation only reduces the increase of flux induced by H1-activation. H1-activation induces a release of Ca from the intracellular Ca stores, while H2-activation inhibits this release.

Animals↗
PubMed1979

Activation of contraction of arterial smooth muscle in the presence of nitrate and other anions.

Contraction strength was measured in ear artery and aorta of the rabbit and coronary artery of the pig during replacement of chloride with anions of the lyotrophic series. Contractions induced by depolarization with elevated external potassium were potentiated in the presence of foreign anions, while those induced by noradrenaline were affected only at higher concentrations of the drug. Drug induced contractions in calcium-free solutions were not affected by the anions. In the presence of nitrate and excess K the change of membrane potential per tenfold change in (K)o was 56mV in chloride and 50 mV in nitrate solution. Enhancement of contraction strength by nitrate was not associated with alterations in membrane potential. Stimulation of aorta with 29.5 mM K resulted in a larger net uptake of 45Ca in nitrate than in chloride. K-stimulated 45Ca efflux was greater in the ear artery in NO3 solution than Cl solution while 45Ca efflux induced by noradrenaline was not effected by anion replacement. These results suggest that in these arteries anions potentiate contraction by enhancing the influx of external calcium, and do not modify the release of internal stores of calcium.

Animals↗
PubMed1979

Sodium and calcium interactions in vascular smooth muscle cells of the rabbit ear artery.

The effects of Na-free and of K-free solutions on the membrane potential, on tension development, and on 45Ca exchange have been investigated in rabbit ear artery. The contraction induced by Na-free solutions and the tension which develops in K-free solutions after a delay of about 1 h are both submaximal. Exposure for 4 h to K-free solutions does not affect the membrane potential, whereas Na-free solutions depolarize the cells by 10-20 mV, depending on the Na-substitute. Neither the amplitude nor the rate constant of the slowly exchanging 45Ca-fraction is affected by these experimental procedures. Substituting external Na by choline or TMA induces a transient increase of the 45Ca-efflux rate which does not occur in a Ca-free efflux medium, and which can be blocked with La. K readmission to Na-enriched tissues hyperpolarizes the cells up to -100 mV and induces a relaxation, without exerting any effect on the 45Ca efflux rate. The release of Ca from intracellular stores, induced by histamine and FCCP, and its subsequent extrusion through the plasma membrane produce a transient stimulation of the 45Ca efflux, which is not affected by the reduction of the Na gradient. The transient contraction induced by histamine in Ca-free solutions is affected in a different way by different Na substitutes. The results do not fit the Na-Ca exchange hypothesis but are consistent with an effect of the Na gradient on the passive Ca influx.

Animals↗