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K G Morgan

Publications and source records attributed to K G Morgan.

At least 91 records · Page 5Linked to original sources
PubMed1990

The role of calcium in the control of vascular tone as assessed by the Ca2+ indicator aequorin.

An overview is given of the current understanding of the mechanism of contraction of vascular smooth muscle. The regulation of vascular tone by intracellular ionized calcium levels appears to occur primarily through calcium-dependent phosphorylation of the myosin light chains by the enzyme myosin light chain kinase. Evidence is presented that additional relatively calcium-independent processes also exist and contribute to the regulation of vascular tone. A scheme is presented whereby vasoconstriction may occur in the absence of any change in cytoplasmic ionized calcium levels. The multiplicity of excitation-contraction coupling pathways in vascular smooth muscle predicts a multitude of rational therapeutic approaches to vascular pathologies.

Aequorin↗
PubMed1990

The nuclear-cytoplasmic [Ca2+] gradient in single mammalian vascular smooth muscle cells.

We studied the nuclear-cytoplasmic [Ca2+] gradient in single, freshly dispersed smooth muscle cells from the ferret portal vein, by means of fluorescence ratio imaging microscopy. Cells were loaded with the cell-permeant calcium indicator fura-2 AM. Caffeine and platelet-derived growth factor (PDGF) were used in order to mobilize Ca2+ from the sarcoplasmic reticulum. Basal levels of nuclear and cytoplasmic [Ca2+] were 299 +/- 51 nM and 141 +/- 23 nM respectively (n = 10, p less than 0.001). At 3 min after 10mM caffeine, nuclear [Ca2+] decreased to 117 +/- 13 nM (n = 10, p less than 0.001), cytoplasmic [Ca2+] also decreased to 75 +/- 11 nM (n = 10, p less than 0.001) and the nuclear-cytoplasmic difference was no longer significant (p greater than 0.05). Similarly, 300pM of PDGF also abolished the nuclear-cytoplasmic [Ca2+] gradient (n = 12, p greater than 0.1). We conclude that in single muscle cells from the ferret portal vein a perinuclear sarcoplasmic reticulum could be a factor that contributes to the high apparent nuclear Ca2+ levels either through a dynamic Ca2+ influx, or by a fura-2 signal in the sarcoplasmic reticulum masking the true nuclear [Ca2+].

Animals↗
PubMed1990

Effects of calcium on vascular smooth muscle tone.

It is generally acknowledged that calcium plays a major role in the generation of vascular tone. However, in recent years it has become increasingly evident that relatively calcium-insensitive pathways of excitation-contraction coupling also exist in the vascular smooth muscle cell. Possible mechanisms of vascular smooth muscle contraction and their possible role in the pathophysiology of hypertension are reviewed. The rationale for the use of calcium channel blockers in the treatment of hypertension is discussed.

Calcium↗
PubMed1989

Pathophysiologic role of calcium in the development of vascular smooth muscle tone.

Recent information indicates that the intracellular ionized calcium concentration [Ca2+]i plays a regulatory role not only in determining the magnitude of vascular tone but also in regulating growth of vascular tissue. Studies on living vascular smooth muscle cells using the calcium indicator aequorin have revealed that the relation between [Ca2+]i and contraction of the vascular smooth muscle cell is complex. More than 1 intracellular kinase may be involved, leading to the coexistence of multiple excitation-contraction coupling pathways. However, it appears that all of these pathways may be calcium-dependent. It is not yet known whether the cause of human essential hypertension involves an elevated [Ca2+]i in the vascular smooth muscle cell. However, evidence is presented supporting the concept that a decreased [Ca2+]i in the hypertensive smooth muscle cell will lead to a decrease in vascular tone and total peripheral resistance, and possibly also antagonize the growth response of the vascular smooth muscle cell associated with the secondary effects of hypertension.

Animals↗
PubMed1989

Agonist-specific myosin phosphorylation and intracellular calcium during isometric contractions of arterial smooth muscle.

The relationship between phosphorylation of the 20-kDa myosin light chain, intracellular calcium levels ([Ca2+]i), and isometric force was studied during prolonged activation of arterial smooth muscle. Aequorin, preloaded into ferret aortic strips, was used as a [Ca2+]i indicator. Two dimensional polyacrylamide gel electrophoresis was used to determine the phosphorylation levels of the 20-kDa myosin light chain (LC20). During the 30-min depolarization of arterial smooth muscle by K+ (21 mM), both LC20 phosphorylation and [Ca2+]i increased significantly at all time points examined as did the steady state stress. A transient rise in LC20 phosphorylation and [Ca2+]i occurred within 30 s, followed by suprabasal levels through the 10-min period during a sustained alpha 1-mediated activation by 10(-5) M phenylephrine whereas a higher force was developed at a shorter time compared to K+. An active phorbol ester 12-deoxyphorbol 13-isobutyrate 20-acetate (DPBA, 10(-6) M) induced a slow contraction of similar magnitude to that induced by K+ without significantly changing either [Ca2+]i or LC20 phosphorylation over a 90-min period. These results demonstrate that the amount of LC20 phosphorylation correlates with the [Ca2+]i in all three types of activation. The initial levels of [Ca2+]i and LC20 phosphorylation correlate with the onset of force development but not the magnitude of steady state stress, suggesting a role for [Ca2+]i and LC20 phosphorylation in regulating the cross bridge cycling rate during tension development. The lack of a detectable increase in [Ca2+]i and LC20 phosphorylation during DPBA activation suggests that sites other than LC20, phosphorylated by protein kinase C, may be involved in regulating smooth muscle contraction.

Animals↗
PubMed1989

Involvement of the protein kinase C system in calcium-force relationships in ferret aorta.

1. Intracellular Ca2+-force relationships were investigated in ferret aortic smooth muscle by the simultaneous measurement of aequorin luminescence and isometric force. Complete calcium-force curves were constructed by plotting calibrated aequorin luminescence versus force, while intracellular [Ca2+] was made to change by increasing degrees of K+ depolarization or decreasing extracellular [Ca2+]. 2. The steady state calcium-force curve in response to K+ depolarization exhibited maximal force generation at an intracellular [Ca2+] of approximately 4 x 10(-7) M. Further increases in intracellular [Ca2+] did not yield additional increments in force. 3. Protein kinase C activation with the phorbol ester, 12-deoxyphorbol-13-isobutyrate 20 acetate (DPBA) produced contractions accompanied by no detectable increases in aequorin luminescence. DPBA significantly shifted the control [Ca2+]-force relationship leftward to lower intracellular [Ca2+] with an increase in the magnitude of maximal generated force. 4. In aorta maximally precontracted by K+ depolarization, the addition of DPBA resulted in a significant increase in force in the absence of further increases in intracellular [Ca2+]. Conversely, in muscles maximally precontracted with DPBA, responses to K+ depolarization resulted in subsequent increases in force in the presence of simultaneous sustained increases in intracellular [Ca2+]. 5. The relatively specific protein kinase C antagonist H-7 caused a significant decrease in intrinsic myogenic tone in the absence of any statistically significant decrease in intracellular [Ca2+]. 6. These results suggest that protein kinase C may be an important regulator of vascular smooth muscle contractility by: (1) providing a mechanism by which the apparent [Ca2+] sensitivity of the contractile apparatus during agonist-induced contractions is increased, and (2) maintaining intrinsic myogenic tone by a mechanism the [Ca2+] requirement of which is satisfied by the resting [Ca2+]i.

Animals↗
PubMed1989

Calcium-force coupling mechanisms during vasodilator-induced relaxation of ferret aorta.

1. The effects of three vasodilators, nifedipine, hydralazine and forskolin, were determined on isometric force and intracellular ionized calcium concentration ([Ca2+]i) as indicated by aequorin in ferret aorta. Three types of contraction were studied: the intrinsic tone induced by warming from 22 to 37 degrees C; the contraction to the phorbol ester 12-deoxyphorbol-13-isobutyrate-20-acetate (DPBA); and the contraction to potassium depolarization. 2. On warming there was no significant steady-state change in [Ca2+], even though 5.7 +/- 0.7 mN of tone developed. During potassium depolarization, [Ca2+]i rose to a sustained plateau while DPBA caused no significant rise in [Ca2+]i. 3. Nifedipine and hydralazine inhibited intrinsic tone while causing an associated decrease in [Ca2+]i; but in the presence of forskolin, a similar inhibition of tone was accompanied by no significant decrease in [Ca2+]i. 4. Nifedipine and hydralazine prolonged the characteristic lag phase before force development in response to DPBA but did not cause a significant change in contraction amplitude. In contrast, forskolin caused an essentially total inhibition of the contraction. 5. During potassium depolarization, all three vasodilators caused significant decreases in [Ca2+]i coincident with decreases in steady-state force. Calcium-force curves were constructed by plotting the calibrated aequorin light signal against the resulting force. The control calcium-force curve was not shifted by nifedipine or hydralazine but was significantly shifted to the right by forskolin.

Animals↗
PubMed1989

Stimulus-specific changes in mechanical properties of vascular smooth muscle.

To determine whether the mechanical properties of vascular smooth muscle are stimulus specific, force, stiffness, and the unloaded shortening velocity (Vmax) were measured during contractions of aortic smooth muscle strips stimulated with phenylephrine or KCl. After activation, muscle force and stiffness rose to a steady-state plateau where they were maintained. In phenylephrine contractions, Vmax peaked during force development and then fell to a lower steady-state level during force maintenance, whereas in the KCl contractions, Vmax did not decline during sustained contractions. Stimulation with KCl, compared with phenylephrine, produced lower steady-state forces. One possible interpretation is that the muscle formed latch cross-bridges during phenylephrine contractions, but not during KCl depolarizations. The slope of the plot of relative muscle force vs. stiffness for phenylephrine contractions, compared with KCl depolarizations, was reduced. This may imply tht the relative force per attached latch crossbridge could be reduced.

Animals↗
PubMed1989

Differences in alpha-adrenergic responsiveness between human internal mammary arteries and saphenous veins.

Little is known regarding specific biologic and pharmacologic differences between human internal mammary arteries and saphenous veins. To better define the role of alpha-adrenoceptor-mediated vasoconstriction in human internal mammary arteries and saphenous veins, we obtained fresh specimens of both vessels from 32 patients undergoing coronary artery bypass surgery. Dose-response curves were generated for the relatively selective alpha 1-receptor agonist phenylephrine, the alpha 2-receptor agonist BHT-920, and the alpha 1- and alpha 2-receptor agonist norepinephrine. Phenylephrine elicited similar contractile responses in internal mammary arteries and saphenous veins, with a mean EC50 (the effective concentration necessary to produce 50% of the maximal contraction) of 1.4 X 10(-6) M for internal mammary arteries and 1.8 X 10(-6) M for saphenous veins (p = NS). Selective stimulation of alpha 2-receptors with BHT-920 elicited a marked contractile response only in saphenous veins. Dose-response curves for phenylephrine and BHT-920 were shifted to the right for both vessels in the presence of the alpha 1-receptor antagonist prazosin and the alpha 2-receptor antagonist yohimbine, respectively. Norepinephrine elicited contraction at a lower concentration in saphenous veins than in internal mammary arteries with a mean EC50 of 7.8 X 10(-8) M for saphenous veins and a mean EC50 of 3.4 X 10(-7) M for internal mammary arteries (p less than 0.05). The results suggest that alpha-adrenoceptor-mediated vasoconstriction is caused primarily by alpha 1-receptors in human internal mammary arteries and by alpha 1- and alpha 2-receptors in human saphenous veins.

Adrenergic alpha-Agonists↗
PubMed1988

Hodgkin's disease: a flow cytometric study.

Flow cytometry was performed on paraffin embedded tissue from 115 cases of Hodgkin's disease. Thirteen (11%) tumours were aneuploid with no significant difference between the histological subgroups. The median proliferative index was 14%, and the highest values were found in the NS2 (16.4%) and lymphocyte depleted (16.0%) subgroups. The difference in proliferative index approached significance when the NS2 subgroup was compared with the NS1 subgroup (p less than or equal to 0.11) and when the lymphocyte depleted and NS2 subgroups combined were compared with the mixed cellularity, lymphocyte predominance, and NS1 subgroups combined (p less than or equal to 0.07). There was a trend towards better survival for patients with aneuploid tumours and those cases with a proliferative index below 15%, but neither of these trends was significant.

Adolescent↗
PubMed1987

Calcium and vascular smooth muscle tone.

Recent technologic advances have improved the monitoring of intracellular ionized calcium concentrations ([Ca2+]i) in living vascular smooth muscle cells. The changes in cytoplasmic ionized calcium concentrations ([Ca2+]) that occur during a contraction-relaxation cycle of vascular smooth muscle are reviewed, as is recent evidence indicating that vascular smooth muscle tone can be increased by increasing the sensitivity of the contractile apparatus to calcium without a necessary change in [Ca2+]i levels. Data obtained using intracellular calcium indicators suggest that agonists that produce similar force profiles often produce very different profiles in [Ca2+]i. The amount of force produced at a specific level of [Ca2+]i is a variable of intact vascular smooth muscle, i.e., some agonists produce sizable tonic contractions with little elevation of cytoplasmic [Ca2+], whereas other agonists require much larger increases in cytoplasmic [Ca2+] to produce comparable increases in tone. These data also indicate that very small changes in [Ca2+]i can cause large changes in vascular tone. Designing therapeutic agents that would decrease [Ca2+]i or decrease the sensitivity of the contractile apparatus to ionized calcium would directly decrease intrinsic myogenic tone. Although a causative role for abnormal [Ca2+]i in the etiology of hypertension is controversial, it is obvious that a decrease in these levels in the vascular smooth muscle cell could be therapeutically beneficial.

Animals↗
PubMed1987

Role of calcium ion in maintenance of vascular smooth muscle tone.

Recent evidence indicates that vascular smooth muscle tone can be increased either by increasing cytoplasmic calcium ion (Ca++) levels or by increasing the sensitivity of the contractile apparatus to calcium. Data obtained with both luminescent and fluorescent calcium indicators indicate that the amount of force produced at a specific Ca++ is variable in intact vascular smooth muscle. Data obtained with the luminescent calcium indicator aequorin indicate that the calcium force curve is very steep in intact vascular smooth muscle cells; i.e., small changes in Ca++ can cause large changes in vascular tone. Therapeutic agents designed to directly decrease intrinsic myogenic tone could be designed to either decrease Ca++ or to decrease the sensitivity of the contractile apparatus to calcium. Considerable selectivity might be obtained by the latter approach.

Animals↗
PubMed1987

Alterations in cytoplasmic calcium sensitivity during porcine coronary artery contractions as detected by aequorin.

1. Intracellular-Ca2+-force relationships were investigated in porcine epicardial coronary arteries by the simultaneous measurement of aequorin luminescence and isometric force. 2. In response to K+ depolarization and histamine, force and aequorin light rose monophasically. In response to carbachol and serotonin, tonic contractions were accompanied by biphasic aequorin signals consisting of an initial spike followed by a low plateau. Contractions produced by prostaglandin F2 alpha (PGF2 alpha) or the endoperoxide analogue U-46619 were accompanied by little or no detectable rise in light. 3. Comparison of steady-state force to steady-state light levels indicated that agonists gave greater force for a given intracellular Ca2+ concentration ([Ca2+]i) compared to that seen during K+ contractures. 4. In Ca2+-free bathing media, carbachol produced a transient contraction accompanied by a transient intracellular Ca2+ spike indicating release of Ca2+ from intracellular storage sites. 5. In Ca2+-free bathing media PGF2 alpha produced a tonic contraction with no detectable change in light. 6. These results suggest that changes in the sensitivity of the contractile apparatus to Ca2+ or other activator systems may be as important a mechanism of contraction as are changes in [Ca2+]i.

Aequorin↗
PubMed1987

Intracellular calcium levels in phorbol ester-induced contractions of vascular muscle.

Intracellular calcium concentration ([Ca2+]i) was measured with aequorin in ferret and rat aortic strips contracted with phorbol esters. In ferret aorta, 12-deoxyphorbol 13-isobutyrate 20-acetate (DPBA, 1 microM) induced contractions without significantly increasing [Ca2+]i, whereas 21 mM K+ induced smaller contractions with a significant rise in [Ca2+]i. Ca2+-free 2.5 mM ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA)-physiological saline solution (PSS) had no effect on DPBA-induced tension, whereas it abolished contractions induced by 66 mM K+. The alpha 1-adrenergic agonist phenylephrine (10(-5) M) induced less than 10% of the tension with no initial [Ca2+]i spike under Ca-free conditions. In rat aorta, both phorbol 12-myristate 13-acetate (PMA, 2 microM) and DPBA (1 microM) induced contractions without increasing [Ca2+]i; Ca2+-free EGTA-PSS or the addition of the calcium channel blocker gallopamil (D600, 1 microM), however, abolished greater than 50% of the tension induced by either phorbol ester with a decrease in [Ca2+]i. These results are consistent with the idea that 1) resting [Ca2+]i is both sufficient and required to support phorbol ester-induced contractions in two vascular smooth muscles, suggesting an increased sensitivity of the contractile apparatus for Ca2+, and 2) there are differences in the mechanisms by which phorbol esters and alpha 1-agonists may activate vascular smooth muscle.

Animals↗
PubMed1987

Ca2+ signals obtained with multiple indicators in mammalian vascular muscle cells.

Enzymatically isolated single cells from ferret portal vein were loaded with the fluorescent dyes fura-2 and chlortetracycline. Ferret portal vein intact strips were loaded with the luminescent indicator aequorin. At short loading times, fura-2 loading resulted in relatively homogeneous images of labeled cells. At longer loading times, extremely heterogeneous images were obtained that were similar to those produced by chlortetracycline, an indicator recognized to enter calcium-storage organelles. A significant effect of fura-2 on contractile function was detected at the long but not at the short loading time. Caffeine, which is known to deplete calcium from sarcoplasmic reticulum, decreased the fura-2 fluorescent intensity when cells were incubated for a long loading time but caused no statistically significant change at the short loading time. Caffeine caused no drop in the aequorin signal but did cause a drop in the chlortetracycline fluorescence. These results are consistent with the idea that aequorin reports cytoplasmic intracellular calcium concentration ([Ca2+]i), chlortetracycline reports stored calcium, and fura-2 reports a mixed signal from the cytoplasm and calcium-storage organelles depending on incubation time.

Aequorin↗
PubMed1986

A comparison of two different indicators: quin 2 and aequorin in isolated single cells and intact strips of ferret portal vein.

A comparison between the fluorescent indicator quin 2 and the bioluminescent indicator aequorin was performed in the same smooth muscle cell type. Aequorin was loaded into intact strips and quin was loaded into enzymatically isolated single cells from ferret portal vein. Both indicators gave qualitatively the same calcium profiles when the tissue was challenged with agonists. Quin loading caused a dramatic shift to the right in dose response curves to potassium and phenylephrine. The ED50 values for quin loaded cells were significantly different from those for control cells for both agonists. Intracellular calcium levels at rest were not significantly different with quin and aequorin. Cells stimulated with potassium gave significantly different intracellular calcium values with the two indicators suggesting a change in the stimulated steady state level due to the introduction of an additional calcium buffer (quin2) into the cell.

Aequorin↗