Sources of Calcium for Contraction of Guinea‐pig Isolated Tracheal Smooth Muscle

Tissue bath experiments showed that potassium chloride (KCl) at 10–40 mmol l−1 evoked spasm of guinea‐pig trachealis which was unaffected by atropine (1 μmol l−1), mepyramine (1 μmol l−1), tetrodotoxin (3 μmol l−1) or indomethacin (2.8 μmol l−1). Spasm evoked by KCl was depressed in Ca2+‐free Krebs solution or by exposure of tissues to LaCl3 (0.25–1 mmol l1). Extracellular electrical; recording showed that the spasm evoked by KCl 10 mmol l−1 was associated with promotion of electrical slow wave activity. Higher concentrations of KCl abolished slow wave activity but caused further tension development. Intracellular recording confirmed the ability of KCl 10 mmol l−1 transiently to promote slow wave activity in individual trachealis cells. This action was associated with depolarization and tension development. Higher concentrations of KCl evoked further tension development but slow waves were suppressed as the depolarization evoked by KCl increased. KCl (10–40 mmol 1−1) increased the lanthanum‐resistant calcium fraction of muscle‐containing strips of trachea. It is concluded that KCl acts directly on the smooth muscle of guinea‐pig trachea. The spasmogenic action is associated with transient promotion of slow wave activity and a fall in resting membrane potential. The spasm involves the cellular influx of Ca2+ and is dependent on the presence of Ca2+ in the extracellular fluid.

Section: Intracellularelectrophysiological Recordingmentioning

confidence: 99%

Section: Intracellularelectrophysiological Recordingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The spasmogenic action of potassium chloride in guinea‐pig trachealis

Foster

Small

Weston

1983

“…Conversely, prolonged exposure to EGTA may not only affect the residual extracellular calcium ions, it may also remove calcium from the intracellular stores. In the present study, the protocol described by Creese & Denborough (1981) The contraction induced by the addition of endothelin to the organ baths was extremely slow in onset. Its prolonged nature was similar to the contraction which results from the application of leukotrienes to isolated bronchial tissue (Hanna et al, 1981).…”

Section: Autoradiographic Studiesmentioning

confidence: 99%

The mechanism of action of endothelin in human lung

McKay

Black

Armour

1991

1 The peptides endothelin-1 (ET-1) and endothelin-2 (ET-2) elicited potent and sustained contractions of human isolated bronchus and pulmonary artery. 2 ET-1 is one of the most potent contractile agonists investigated in these tissues with an EC50 value of 18.3 nm (95% confidence interval: 12.9, 25.9 nM; n = 26) in bronchus and 3.2 nm (95% confidence interval: 0.4, 23.9 nM; n = 5) in the arterial preparation. 3 ET-1 is 2.5 times more potent than ET-2 in both the airway and vascular tissues, and both forms of the peptide have geometric mean EC50 values 5 times greater in the isolated bronchial tissue than in the pulmonary artery.4 Neither pretreatment with the voltage-dependent calcium (VDC) channel antagonist verapamil (1O#M) nor with indomethacin (25 pM) significantly altered the response curve to ET-1 in human isolated bronchus. Removal of calcium from the Krebs-Henseleit solution did not affect ET-1-induced responses. 5 Specific binding on the smooth muscle of human airway and pulmonary arterial tissue to both ET-1 and ET-2 was detected in autoradiographic studies. There appeared to be no difference between the peptides in the location nor the density of binding sites. 6 We conclude that contraction of human bronchial tissue by ET-1 is not dependent upon influence of extracellular calcium nor release of prostaglandins or thromboxane A2. It is likely that the action of ET-1 in this tissue is due to binding of this peptide to specific receptors located on the smooth muscle.

“…More recently a new subtype, the EP4 receptor, has been described (Coleman et al, 1994a). EPI receptors are present in smooth muscles, mediate a contractile response (Lawrence et al, 1992;Sheldrick et al, 1988), and have been shown to be coupled to phosphoinositide hydrolysis through regulatory G proteins (Creese & Denborough, 1981). There are selective agonists for the EPI receptor but none is highly selective, while several specific antagonists have been developed (Coleman et al., British Journal of Pharmacology (1996) 118,[1597][1598][1599][1600][1601][1602][1603][1604] A.i.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the PGE₂ receptor subtype in bovine chondrocytes in culture

Brum‐Fernandes

Morisset

Bkaily

et al. 1996

1 Prostaglandin E2 (PGE2) is an autacoid that decreases proteoglycan synthesis, increases metalloprotease production by cultured chondrocytes, and can modulate some of the actions of interleukin-l on cartilage. The objective of the present study was to characterize the subtype of prostaglandin E2 receptor present in bovine chondrocytes in culture. 2 Primary cultures of articular chondrocytes were prepared from slices of bovine carpal cartilage by sequential digestion with type III hyaluronidase, trypsin, type II collagenase, followed by overnight incubation in Dulbecco's Modified Eagle's Medium (DMEM) with type II collagenase, washing, and seeding at a density of 2 x 105 cells cm-2 in DMEM with 10% foetal bovine serum.3 PGE2 and carbaprostacyclin induced dose-dependent increases in intracellular cyclic AMP in bovine chondrocytes in culture. The potencies of these compounds were different, and maximal doses of PGE2 and carbaprostacyclin had an additive effect. PGD2 induced a small increase in intracellular cyclic AMP only at a high concentration (10-' M).4 PGE2 was more potent that the EP2 agonist 11-deoxy-PGE, at inducing increases in intracellular cyclic AMP. The EP2 agonist butaprost, however, induced only a small increase at a concentration of l0-5 M. 17-Phenyl-PGE2 (EPI agonist), sulprostone and MB 28767 (15S-hydroxy-9-oxo-16-phenoxy-wotetranorprost-13E-enoic acid) (EP3 agonists) did not induce an increase in intracellular cyclic AMP at concentrations up to l0-' M. The EP4 antagonist AH 23848B ([1a(Z),2fl,5a]-(±)-7-[5-[[(l,1'-biphenyl)-4-yl]methoxy]-2-(4-morpholinyl)-3-oxocyclopentyl]-5-heptenoic acid) antagonized PGE2 but not carbaprostacyclin effects on intracellular cyclic AMP. The Schild plot slope was different from 1 but this could be due to an interaction of PGE2 with IP receptors in high doses. The exact nature of the antagonism by compound AH 23848B could not be definitely established in these experimental conditions. 6 Neither PGE2 nor any of its analogues inhibited the increase in intracellular cyclic AMP induced by forskolin, and pertussis toxin did not alter the response to PGE2, suggesting that no Gi-coupled PGE2 receptors are present in these cells. Stimulation with PGE2 did not induce significant increases in intracellular inositol-trisphosphate levels nor increases in intracellular free calcium as determined by confocal microscopy, suggesting the absence of phospholipase-C-coupled or of calcium channel-coupled PGE2 receptors in bovine chondrocytes in these experimental conditions. 7 These results show for the first time that bovine chondrocytes in culture present a functional PGE2 receptor that has some pharmacological characteristics of an EP4 subtype, as well as an IP receptor.