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Trappanese DM, Sivilich S, Ets HK, Kako F, Autieri MV, Moreland RS. Regulation of mitogen-activated protein kinase by protein kinase C and mitogen-activated protein kinase phosphatase-1 in vascular smooth muscle. Am J Physiol Cell Physiol 2016; 310:C921-30. [PMID: 27053523 DOI: 10.1152/ajpcell.00311.2015] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Accepted: 04/04/2016] [Indexed: 01/08/2023]
Abstract
Vascular smooth muscle contraction is primarily regulated by phosphorylation of myosin light chain. There are also modulatory pathways that control the final level of force development. We tested the hypothesis that protein kinase C (PKC) and mitogen-activated protein (MAP) kinase modulate vascular smooth muscle activity via effects on MAP kinase phosphatase-1 (MKP-1). Swine carotid arteries were mounted for isometric force recording and subjected to histamine stimulation in the presence and absence of inhibitors of PKC [bisindolylmaleimide-1 (Bis)], MAP kinase kinase (MEK) (U0126), and MKP-1 (sanguinarine) and flash frozen for measurement of MAP kinase, PKC-potentiated myosin phosphatase inhibitor 17 (CPI-17), and caldesmon phosphorylation levels. CPI-17 was phosphorylated in response to histamine and was inhibited in the presence of Bis. Caldesmon phosphorylation levels increased in response to histamine stimulation and were decreased in response to MEK inhibition but were not affected by the addition of Bis. Inhibition of PKC significantly increased p42 MAP kinase, but not p44 MAP kinase. Inhibition of MEK with U0126 inhibited both p42 and p44 MAP kinase activity. Inhibition of MKP-1 with sanguinarine blocked the Bis-dependent increase of MAP kinase activity. Sanguinarine alone increased MAP kinase activity due to its effects on MKP-1. Sanguinarine increased MKP-1 phosphorylation, which was inhibited by inhibition of MAP kinase. This suggests that MAP kinase has a negative feedback role in inhibiting MKP-1 activity. Therefore, PKC catalyzes MKP-1 phosphorylation, which is reversed by MAP kinase. Thus the fine tuning of vascular contraction is due to the concerted effort of PKC, MAP kinase, and MKP-1.
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Affiliation(s)
- Danielle M Trappanese
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania; Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, Pennsylvania; and
| | - Sarah Sivilich
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Hillevi K Ets
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Farah Kako
- Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, Pennsylvania; and
| | - Michael V Autieri
- Cardiovascular Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, Pennsylvania; and
| | - Robert S Moreland
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania; Department of Pathology and Laboratory Medicine, Drexel University College of Medicine, Philadelphia, Pennsylvania
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Rembold CM, Ripley ML, Meeks MK, Geddis LM, Kutchai HC, Marassi FM, Cheung JY, Moorman JR. Serine 68 phospholemman phosphorylation during forskolin-induced swine carotid artery relaxation. J Vasc Res 2005; 42:483-91. [PMID: 16155364 PMCID: PMC1266286 DOI: 10.1159/000088102] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2005] [Accepted: 06/26/2005] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Phospholemman (PLM) is an abundant phosphoprotein in the plasma membrane of cardiac, skeletal and smooth muscle. It is a member of the FXYD family of proteins that bind to and regulate the Na,K-ATPase. Protein kinase A (PKA) is known to phosphorylate PLM on serine 68 (S68), although the functional effect of S68 PLM phosphorylation is unclear. We therefore evaluated S68 PLM phosphorylation in swine carotid arteries. METHODS Two anti-PLM antibodies, one to S68 phosphorylated PLM and one to unphosphorylated PLM, were made to PLM peptides in rabbits and tested with purified PLM and PKA-treated PLM. Swine carotid arteries were mounted isometrically, contracted, relaxed with forskolin and then homogenized. Proteins were separated on SDS gels and the intensity of immunoreactivity to the two PLM antibodies determined on immunoblots. RESULTS The antipeptide antibody 'C2' primarily reacted with unphosphorylated PLM, and the antipeptide antibody 'CP68' detected S68 PLM phosphorylation. Histamine stimulation of intact swine carotid artery induced a contraction, increased the CP68 PLM antibody signal and reduced the C2 PLM antibody signal. High extracellular [K(+)] depolarization induced a contraction without altering the C2 or CP68 PLM signal. Forskolin-induced relaxation of histamine or extracellular [K(+)] contracted arteries correlated with an increased CP68 signal. Nitroglycerin-induced relaxation was not associated with changes in the C2 or CP68 PLM signal. CONCLUSIONS These data suggest that a contractile agonist increased S68 PLM phosphorylation. Agents that increase [cAMP], but not agents that increase [cGMP], increased S68 PLM phosphorylation. S68 PLM phosphorylation may be involved in cAMP-dependent regulation of smooth muscle force.
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Affiliation(s)
- Christopher M Rembold
- Cardiovascular Division, Department of Internal Medicine, University of Virginia Health System, Charlottesville, VA 22908, USA.
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Horiguchi S, Watanabe J, Kato H, Baba S, Shinozaki T, Miura M, Fukuchi M, Kagaya Y, Shirato K. Contribution of Na+/Ca2+ exchanger to the regulation of myogenic tone in isolated rat small arteries. ACTA PHYSIOLOGICA SCANDINAVICA 2001; 173:167-73. [PMID: 11683674 DOI: 10.1046/j.1365-201x.2001.00872.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The contribution of the Na+/Ca2+ exchanger to the myogenic vascular tone was examined in rat isolated skeletal muscle small arteries (ASK) with pronounced myogenic tone and mesenteric small arteries (AMS) with little myogenic tone. Myogenic tone was assessed by the vascular inner diameter at transmural pressures of 40 and 100 mmHg. To depress the Na+/Ca2+ exchanger, the extracellular Na+ concentration ([Na+]o) was lowered from 143 to 1.2 mM by substituting choline-Cl for NaCl. The ASK developed significant myogenic tone and constricted further in low [Na+]o. Nifedipine (1 microM) reduced both myogenic tone and low [Na+]o-induced contraction. Because the membrane potential of ASK was not changed by low [Na+]o (-35 +/- 2 mV at 143 mM [Na+]o, -37 +/- 3 mV at 1.2 mM [Na+]o), depolarization-induced Ca2+ influx was not a cause of the low [Na+]o-induced contraction. The AMS did not develop significant myogenic tone. Although low [Na+]o also constricted AMS, the magnitude of constriction was significantly weaker than that in ASK (17 +/- 4 vs. 47 +/- 6%, P < 0.01, at 58 mM Na+). With Bay K 8644, AMS developed myogenic tone, and low [Na+]o-induced constriction was significantly increased. In conclusion, Na+/Ca2+ exchanger may play an important role in regulating myogenic tone, likely via mediating Ca2+-extrusion.
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Affiliation(s)
- S Horiguchi
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan
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4
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Davel AP, Rossoni LV, Vassallo DV. Effects of ouabain on the pressor response to phenylephrine and on the sodium pump activity in diabetic rats. Eur J Pharmacol 2000; 406:419-27. [PMID: 11040349 DOI: 10.1016/s0014-2999(00)00679-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The diabetes mellitus insulin-dependent is usually associated with cardiovascular disorders and with changes in the activity of the Na(+),K(+)-ATPase. The effects of ouabain, a Na(+),K(+)-ATPase inhibitor, on the pressor response of 7-day streptozotocin-induced diabetes were investigated in anesthetized rats and on the vascular reactivity of the perfused rat tail vascular bed. Diabetes was characterized by hyperglycemia (86+/-7.8 vs. 471+/-18.5 mg/dl) without changes in arterial blood pressure. Blood pressure increased after the treatment with 18 microg/kg ouabain in controls but not in diabetic rats; acute hyperglycemia, in non-treated rats, did not change these effects. Control tail vascular beds showed increased maximal response to phenylephrine after treatment with 10 nM ouabain for 1 h; this response was abolished in streptozotocin-treated rats. These rats showed an increased sensitivity to phenylephrine without changing the maximal vasoconstrictor response when compared to control rats. The relaxation induced by acetylcholine was reduced in diabetic rats. The functional activity of the Na(+),K(+)-ATPase was inhibited in vascular beds from diabetic rats, when compared to control rats, and the inhibition of the Na(+),K(+)-ATPase with 10 nM ouabain was not effective in these rats. Results suggested that in 7-day diabetic rats, the increase of arterial blood pressure or the sensitization of the vascular bed produced by ouabain is lost as a consequence of the reduction of the functional activity of the Na(+), K(+)-ATPase probably as a result of insulin lack and a deficient endothelial nitric oxide activity.
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Affiliation(s)
- A P Davel
- Department of Physiological Sciences, Federal University of Espirito Santo, Av. Marechal Campos 1468, 29040-095, ES, Vitoria, Brazil.
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Nilsson H. Interactions between membrane potential and intracellular calcium concentration in vascular smooth muscle. ACTA PHYSIOLOGICA SCANDINAVICA 1998; 164:559-66. [PMID: 9887978 DOI: 10.1046/j.1365-201x.1998.00435.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The intracellular calcium concentration is a major determinant of vascular tone. In the steady state it is regulated mainly by membrane potential. At the same time, several mechanisms regulating the calcium concentration, including the membrane potential, are influenced by the intracellular calcium concentration itself. There are thus multiple possible positive and negative feedback loops involved in calcium regulation. This review gives a brief overview of the different mechanisms involved, including calcium-dependent ion channels, exchangers, and ATPases, and discusses their role in agonist-mediated responses, in relation primarily to studies on the portal vein and mesenteric small arteries.
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Affiliation(s)
- H Nilsson
- Department of Pharmacology, Aarhus University, Denmark
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Rembold CM, Chen XL. The buffer barrier hypothesis, [Ca2+]i homogeneity, and sarcoplasmic reticulum function in swine carotid artery. J Physiol 1998; 513 ( Pt 2):477-92. [PMID: 9806997 PMCID: PMC2231286 DOI: 10.1111/j.1469-7793.1998.477bb.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
1. The goal of this study was to evaluate the buffer barrier hypothesis in an intact arterial smooth muscle. Specifically, we investigated the interrelationships between intracellular [Ca2+] ([Ca2+]i) homogeneity and sarcoplasmic reticulum function in swine carotid artery. 2. We measured focal changes in [Ca2+]i by exploiting the different characteristics of several [Ca2+]i indicators: (1) aequorin, which can detect focal increases in [Ca2+]i such as those that occur in the subplasmalemmal region ([Ca2+]pm); (2) fura-2, which is primarily a measure of mean cytoplasmic [Ca2+] ([Ca2+]c); and (3) force, which reflects increases in [Ca2+] near the contractile apparatus. We then estimated the relative degree of [Ca2+]i homogeneity with the aequorin/fura-2 ratio. Finally, we inhibited sarcoplasmic reticulum Ca2+ pumping with cyclopiazonic acid (CPA), an inhibitor of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA). 3. We found that, after Ca2+ depletion, the sarcoplasmic reticulum could be partially reloaded with Ca2+ by manipulations that increased the aequorin signal relatively more than the fura-2 signal. Complete reloading required large increases in the fura-2 signal. These data suggest that increases in [Ca2+]pm (as measured with aequorin) can partially reload the sarcoplasmic reticulum, but complete reloading required increases in [Ca2+]c (as measured with fura-2). Reloading could be partially inhibited by 10 microM CPA, indicating that SERCA function was important for reloading. 4. In unstimulated arteries, 10 microM CPA increased the fura-2 signal without altering the aequorin signal, thereby decreasing the aequorin/fura-2 ratio. Removal of extracellular Ca2+ without CPA also reduced the aequorin/fura-2 ratio. These data suggest that resting cells have a [Ca2+] gradient with [Ca2+]pm > [Ca2+]c; this gradient is maintained by SERCA function. 5. CPA slowed the decline in the fura-2 signal observed when histamine stimulation was removed. This result is consistent with the concept of vectorial Ca2+ efflux in which Ca2+ pumping by SERCA reduces [Ca2+]c after stimulation. 6. Ca2+ depletion by prior treatment with 100 microM histamine and CPA transiently attenuated subsequent histamine-induced aequorin and fura-2 transients. The effect on contraction was smaller: a delay in contraction of approximately 10 s. These data suggest that histamine-induced Ca2+ release has at least a small role in the initial phase of contraction; however, other contractile mechanisms appear to be able to compensate for loss of Ca2+ release with only modest changes in contraction kinetics. 7. These data suggest that there is a complex interrelationship between smooth muscle sarcoplasmic reticulum function and [Ca2+] in at least two cytoplasmic compartments. [Ca2+]pm and [Ca2+]c can differentially regulate sarcoplasmic reticulum Ca2+ filling; and sarcoplasmic reticulum function regulates [Ca2+]pm and [Ca2+]c.
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Affiliation(s)
- C M Rembold
- Cardiovascular Division, Departments of Internal Medicine and Physiology, University of Virginia Health Science Center, Charlottesville, VA 22908, USA
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Vassallo PF, Stefanon I, Rossoni LV, França A, Vassallo DV. Small doses of canrenone block the effects of ouabain on the mechanical activity of the heart and vessels of the rat. J Cardiovasc Pharmacol 1998; 32:679-85. [PMID: 9821839 DOI: 10.1097/00005344-199811000-00001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Canrenone has been described as an antihypertensive drug that blocks endogenous ouabain effects in volume-dependent hypertensive models. Considering that some canrenone metabolites may be putative mutagenic factors, therapeutic dose reduction might be advantageous if the blockade of ouabain effects is maintained. In this study, the effects of low doses or concentrations of canrenone were investigated in rats by using isolated papillary muscles, Langendorff-perfused hearts, perfused rat-tail vascular bed, and anesthetized animals. Canrenone (0.5, 1, 2, and 5 mg/ml) produced a dose-dependent negative inotropic effect in papillary muscles contracting isometrically and blocked the positive inotropic effect produced by 660 microM ouabain. In Langendorff-perfused hearts beating spontaneously, a low concentration of canrenone (10 microg/ml) increased the isovolumic systolic pressure obtained at several diastolic pressures. Higher concentrations of canrenone (20, 30 microg/ml) brought the isovolumic pressure toward control values, and 100 microg/ml canrenone produced an isovolumic pressure reduction. In these preparations, 20 microg/ml canrenone reduced significantly the positive inotropic effects of 100 microM ouabain. Investigating the vascular smooth muscle reactivity to phenylephrine (PE; 0.5, 1, and 2 microg bolus injections) in the perfused rat-tail vascular bed, it was observed that canrenone blocked completely the enhancement of PE pressor effect produced by 1-h treatment with 100 microM ouabain. Similar results were obtained with the arterial blood pressure reactivity to PE in anesthetized rats. In these animals, canrenone (1 mg/kg) blocked the sensitizing effect of 18 microg/kg ouabain on PE reactivity. In conclusion, results presented here suggest that canrenone may block ouabain effects at very low concentrations. It blocked myocardial positive inotropic effects of ouabain on both papillary muscle and perfused hearts, and the sensitization of PE pressor effects. The results also suggest that canrenone at very small doses might be used to reduce arterial blood pressure in hypertensive conditions accompanied by increased ouabain plasma levels as the main therapeutic procedure or as an adjunct treatment to prevent ouabain sensitizing effects on pressor responses.
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Affiliation(s)
- P F Vassallo
- Department of Physiological Sciences, Federal University of Espirito Santo, Vitória, Brazil
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8
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Adegunloye BJ, Sofola OA. Effect of dietary salt loading and high-calcium diet on vascular smooth muscle responses and endothelium function in rats. Clin Exp Pharmacol Physiol 1997; 24:814-8. [PMID: 9363362 DOI: 10.1111/j.1440-1681.1997.tb02696.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
1. The present study examined the effects of concurrent manipulation of dietary calcium and salt on contractile responses of vascular smooth muscle (VSM) and endothelial function of aortic rings from Sprague-Dawley rats. 2. Salt loading enhanced the contractile response of the aortic rings to noradrenaline (NA), an effect that was blunted by a high calcium intake. 3. Removal of the endothelium and incubation of aortic rings in physiological salt solution containing methylene blue increased the sensitivity of the rings to NA. 4. The increase in the sensitivity of aortic rings induced by endothelium removal was more pronounced in aortic rings from salt-loaded rats. 5. Acetylcholine caused similar degrees of relaxation in all experimental groups, but the relaxation to histamine was smaller (P < 0.05) in salt-loaded rats than in other groups of rats; however, after removal of the endothelium, the contractile response to histamine was higher in salt-loaded rats. 6. The results indicate that the hypersensitivity of isolated aortic rings to agonists, as observed in salt-loaded rats, is due to altered responses of the VSM and not as a result of changes in the endothelium. In addition, salt loading tends to increase the synthesis of endothelium-dependent relaxing factor. The ability of salt loading to enhance the contractile responses of VSM to agonists can be prevented by supplementing the diet with high calcium.
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Affiliation(s)
- B J Adegunloye
- Department of Physiology, College of Medicine, University of Lagos, Nigeria
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Vassallo DV, Songu-Mize E, Rossoni LV, Amaral SM. Effects of ouabain on vascular reactivity. Braz J Med Biol Res 1997; 30:545-52. [PMID: 9251776 DOI: 10.1590/s0100-879x1997000400016] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Ouabain is an endogenous substance occurring in the plasma in the nanomolar range, that has been proposed to increase vascular resistance and induce hypertension. This substance acts on the alpha-subunit of Na+,K(+)-ATPase inhibiting the Na(+)-pump activity. In the vascular smooth muscle this effect leads to intracellular Na+ accumulation that reduces the activity of the Na+/Ca2+ exchanger and to an increased vascular tone. It was also suggested that circulating ouabain, even in the nanomolar range, sensitizes the vascular smooth muscle to vasopressor substances. We tested the latter hypothesis by studying the effects of ouabain in the micromolar and nanomolar range on phenylephrine (PE)-evoked pressor responses. The experiments were performed in normotensive and hypertensive rats in vivo, under anesthesia, and in perfused rat tail vascular beds. The results showed that ouabain pretreatment increased the vasopressor responses to PE in vitro and in vivo. This sensitization after ouabain treatment was also observed in hypertensive animals which presented an enhanced vasopressor response to PE in comparison to normotensive animals. It is suggested that ouabain at nanomolar concentrations can sensitize vascular smooth muscle to vasopressor stimuli possibly contributing to increased tone in hypertension.
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Affiliation(s)
- D V Vassallo
- Departamento de Ciências Fisiológicas, Universidade Federal do Espírito Santo, Vitória, Brasil
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Henrion D, Laher I, Bevan JA. Small changes in extracellular sodium influence myogenic tone in rabbit facial vein by changing its sensitivity to calcium. Life Sci 1997; 60:743-9. [PMID: 9064479 DOI: 10.1016/s0024-3205(96)00653-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Extracellular Na+ concentration ([Na+]e) significantly effects the regulation of myogenic tone in isolated blood vessels. We examined the effect of small changes in [Na+]e on simultaneous changes in stretch-activated myogenic tone in rabbit facial vein and 45Ca2+ unidirectional influx and net uptake. Decreasing [Na+]e from 150 to 120 mmol/l augmented myogenic tone (control: 3.15 +/- 0.27 mN, n = 22) by 89 +/- 29%, while raising [Na+]e to 165 mmol/l attenuated myogenic tone to 80 +/- 2% of control. Changes in myogenic tone induced by alterations in [Na+]e were not accompanied by proportional changes in 45Ca2+ net uptake. 45Ca2+ unidirectional influx per unit of wall force (10.2 +/- 1.0 pmol/mg per mN force, n = 22, control) was decreased to 6.1 +/- 0.6 pmol/mg per mN (n = 20, P < 0.05) and increased to 21.0 +/- 2.5 pmol/mg per mN (n = 14, P < 0.05) when [Na+]e was 120 or 165 mmol/l, respectively, suggesting that decreasing [Na+]e is related to an increased sensitivity to calcium. We conclude that, in the rabbit facial vein, the sensitivity of myogenic tone to changes in [Na+]e may reflect changes in the sensitivity of smooth muscle to Ca2+ through a change in mechanoreceptor sensitivity.
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Affiliation(s)
- D Henrion
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, USA.
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Van Riper DA, Chen XL, Gould EM, Rembold CM. Focal increases in [Ca2+]i may account for apparent low Ca2+ sensitivity in swine carotid artery. Cell Calcium 1996; 19:501-8. [PMID: 8842517 DOI: 10.1016/s0143-4160(96)90059-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Estimates of [Ca2+]i sensitivity in intact smooth muscle are frequently obtained by measuring [Ca2+]i with indicators such as aequorin or Fura-2. We investigated whether focal increases in [Ca2+]i could impair such measures of [Ca2+]i sensitivity. Stimulation of swine carotid artery with 10 microM histamine increased aequorin estimated [Ca2+]i, Fura-2 estimated [Ca2+]i and Ca2+ sensitivity without significantly altering the aequorin/Fura-2 ratio (an estimate of [Ca2+]i homogeneity). Subsequent inhibition of Na+/Ca2+ exchange by replacement of Na+ in the PSS with choline+ significantly increased aequorin-estimated [Ca2+]i but only minimally increased Fura-2 estimated [Ca2+]i, myosin light chain (MLC) phosphorylation and force. This resulted in a large increase in the aequorin/Fura-2 ratio, suggesting an increase in [Ca2+] inhomogeneity. Addition of 100 microM histamine to tissues in the choline+ buffer initially increased both aequorin and Fura-2 estimated [Ca2+]i, but after 10 min exposure both of the [Ca2+]i estimates declined to pre-histamine levels. Histamine addition significantly increased MLC phosphorylation and force, indicating increased Ca2+ sensitivity, but the aequorin/Fura-2 ratio remained elevated and unchanged from pre-histamine values. These data show that under certain conditions, aequorin and Fura-2 can yield widely differing estimates of [Ca2+]i and thus can cause misleading assessments of Ca2+ sensitization mechanisms. These discrepancies may arise from inhomogeneous or focal increases in [Ca2+]i which can be evaluated with the aequorin/Fura-2 ratio.
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Affiliation(s)
- D A Van Riper
- Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908, USA
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Toma CP, Serban DN, Costache V, Branisteanu DD. Characteristics and possible mechanisms of low-Na+ induced contractions in rat aorta. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1995; 352:88-93. [PMID: 7477430 DOI: 10.1007/bf00169194] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The influence of reducing external Na+ concentration ([Na+]ex) upon vascular smooth muscle contractility was investigated using the rat isolated aorta. NaCl from the physiological saline solution (PSS) was replaced with either choline-Cl, sucrose, or LiCl to give the following [Na+]ex (mM): 115, 85, 55, and 25 (115NaPSS to 25NaPSS). Small reductions in [Na+]ex (115NaPSS) induced a biphasic contraction, comparable in amplitude with the control one induced by phenylephrine 10(-6) M. Elimination of the endogenous catecholamine participation using either phentolamine 10(-5) M or guanethidine 3.10(-6) M similarly reduces these contractions to 25% (sucrose replacement). A similar relaxing effect was obtained with D600 10(-5) M, an antagonist of the voltage operated Ca2+ channels (25-30% residual tension for all the substitutes). Large reductions in [Na+]ex (25NaPSS) induced contractions comparable in amplitude and shape, but less sensitive to phentolamine and guanethidine (residual tension 65-75%, sucrose replacement) and insensitive to D600 (all the substitutes). The Na+/K+ ATPase inhibitor ouabain (10(-4) M) elicited slowly developing contractions, the amplitude being 115% of the phenylephrine 10(-6) M control. Phenylephrine further contracted the 115NaPSS precontracted preparations, but was significantly less effective in 25NaPSS, although the precontraction levels were similar for the same substitute used. The amplitude of the superimposed phenylephrine contractions exhibited [Na+]ex dependence. Phenylephrine 10(-6) M failed to further contract the ouabain 10(-4) M precontracted rings. We conclude that relatively small reductions in [Na+]ex are able to induce contractions of rat aorta primarily through release of endogenous catecholamines, probably through neural Na+/Ca2+ exchange. Larger reductions in [Na+]ex appear to cause contraction through muscular Na+/Ca2+ exchange.
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Affiliation(s)
- C P Toma
- University of Medicine and Pharmacy Iasi, Department of Physiology, Romania
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Wright G, Hurn E. Vascular smooth muscle contractile properties in the turtle Pseudemys scripta elegans. ACTA ACUST UNITED AC 1993. [DOI: 10.1016/0742-8413(93)90267-o] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Isenberg G. Ca2+ entry through Na(+)-Ca2+ exchange can trigger Ca2+ release from Ca2+ stores in Na(+)-loaded guinea-pig coronary myocytes. J Physiol 1993; 468:225-43. [PMID: 8254507 PMCID: PMC1143823 DOI: 10.1113/jphysiol.1993.sp019768] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
1. The ionized cytosolic calcium concentration ([Ca2+]i) was monitored in voltage-clamped coronary myocytes at 36 degrees C and 2.5 mM [Ca2+]o using the Ca2+ indicator indo-1. [Ca2+]i was transiently increased by fast application of 10 mM caffeine, and the mechanisms involved in decay of [Ca2+]i were analysed. 2. Resting [Ca2+]i was 166 +/- 62 nM (mean +/- S.D.). Caffeine increased [Ca2+]i within 1-2 s to 1618 +/- 490 nM. In the continuous presence of caffeine [Ca2+]i fell close to resting values with a half-decay time of 5.0 +/- 1.6 s. Wash-out of caffeine induced an undershoot of [Ca2+]i to 105 +/- 30 nM. When caffeine was applied repetitively the [Ca2+]i transients were of reduced amplitude indicating that the store had lost a part of releasable Ca2+. 3. After a 1 s caffeine application [Ca2+]i decayed with a half-time of 2.3 +/- 0.8 s to the undershoot of 112 +/- 57 nM. The decay of [Ca2+]i was largely prevented by 3 mM [La3+]o; after wash-out of La3+ [Ca2+]i fell to the resting value without an undershoot. The results demonstrate that La(3+)-sensitive Ca2+ extrusion contributes to the decay of the [Ca2+]i transient and to the undershoot. 4. With 10 mM [Na+]i, sodium removal from the bath incremented [Ca2+]i in three out of ten cells by 71 +/- 11 nM; in the other cells [Ca2+]i did not change. In the absence of extracellular sodium the decay of [Ca2+]i after wash-out of caffeine was not retarded. 5. To stimulate Na(+)-Ca2+ exchange, cells were dialysed with pipette solution containing 150 mM NaCl. Elevation of [Na+]i had no significant effect on the resting [Ca2+]i (180 +/- 47 nM) or on the caffeine-induced [Ca2+]i transients (peak 1614 +/- 530 nM, half-time of decay 3 s, undershoot 107 +/- 40 nM). 6. With 150 mM [Na+]i, sodium removal resulted in an increase of [Ca2+]i, although responses varied in amplitude (from 130 to 2300 nM) and rate of rise. In the absence of sodium [Ca2+]i remained elevated. After a 1 s caffeine application the undershoot of [Ca2+]i was abolished in sodium-free solution. When caffeine was applied in sodium-free solution, the [Ca2+]i transient decayed to a sustained level and the following caffeine response was attenuated. 7. With 150 mM [Na+]i, the effects of sodium removal were strongly suppressed by a preceding depletion of the Ca2+ stores with caffeine. Ryanodine pretreatment abolished the caffeine-induced [Ca2+]i transients and reduced [Ca2+]i response due to sodium removal.(ABSTRACT TRUNCATED AT 400 WORDS)
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Rapoport RM. Regulation of vascular smooth muscle contraction by extracellular Na+. GENERAL PHARMACOLOGY 1993; 24:531-7. [PMID: 8365636 DOI: 10.1016/0306-3623(93)90209-g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
1. The effects of extracellular Na+ removal on agonist-induced contraction of vascular smooth muscle in vitro are reviewed. 2. The effects of extracellular Na+ removal on contraction vary depending upon the agonist and vessel. 3. Factors that may influence the effects of extracellular Na+ removal on agonist-induced contraction include the compound substituted for Na+, time of tissue exposure to lowered extracellular Na+, concentration of extracellular Na+, agonist concentration, presence of the vascular endothelium and presence of basal tone. 4. The potential influence of these factors needs to be determined and minimized, in studies that investigate the role of extracellular Na+ in agonist-induced contraction.
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Abstract
Intracellular calcium concentration ([Ca2+]i)-dependent activation of myosin light chain kinase and its phosphorylation of the 20-kd light chain of myosin is generally considered the primary mechanism responsible for regulation of contractile force in arterial smooth muscle. However, recent data suggest that the relation between [Ca2+]i and myosin light chain phosphorylation is variable and depends on the form of stimulation. The dependence of myosin phosphorylation on [Ca2+]i has been termed the "[Ca2+]i sensitivity of phosphorylation." The [Ca2+]i sensitivity of phosphorylation is "high" when relatively small increases in [Ca2+]i induce a large increase in myosin phosphorylation. Conversely, the [Ca2+]i sensitivity of phosphorylation is "low" when relatively large increases in [Ca2+]i are required to induce a small increase in myosin phosphorylation. There are two proposed mechanisms for changes in the [Ca2+]i sensitivity of phosphorylation: Ca(2+)-dependent decreases in the [Ca2+]i sensitivity of phosphorylation induced by phosphorylation of myosin light chain kinase by Ca(2+)-calmodulin protein kinase II and agonist-dependent increases in the [Ca2+]i sensitivity of phosphorylation by inhibition of a myosin light chain phosphatase. I will review the proposed mechanisms responsible for the regulation of [Ca2+]i and the [Ca2+]i sensitivity of phosphorylation in arterial smooth muscle.
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Affiliation(s)
- C M Rembold
- Department of Internal Medicine, University of Virginia School of Medicine, Charlottesville
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