ryanodine and 5-nitro-2-(3-phenylpropylamino)benzoic-acid

Sinoaortic denervation is characterized by arterial pressure lability, without sustained hypertension. Aortas isolated from rats with sinoaortic denervation present rhythmic contractions. We studied the participation of distinct Ca(2+) sources in the maintenance of the oscillations. Three days after the surgeries, aortic rings were placed in an organ chamber, and the incidence of aortas presenting rhythmic contractions was measured. Specific drugs were employed to analyse the participation of the Ca(2+) released from the sarcoplasmic reticulum [2-APB (diphenylborinic acid 2-aminoethyl ester), thapsigargin and ryanodine] and external Ca(2+) entry [Bay K 8644, verapamil and DMB (dimethylbenzyl amiloride)] on the rhythmic contractions. Additionally, we verified the effects of chloride channel blocker NPPB [5-nitro-2-(3-phenylpropylamino)-benzoic acid] on the maintenance of the rhythmic contractions. Under phenylephrine stimulus, sinoaortic-denervated rat aortas exhibited rhythmic contractions in the frequency of 4.5 +/- 0.50 cycles/min. and an amplitude of 0.465 +/- 0.05 g. 2-APB, thapsigargin and ryanodine inhibited the rhythmic contractions. Bay K 8644 increased the oscillations, reaching maximum values with a concentration of 50 nM (18.5 +/- 2.5 cycles/min.). The rhythmic contractions were inhibiting by verapamil and Ca(2+)-free solution. DMB and NPPB did not alter the oscillations. In conclusion, we observed that aorta isolated from sinoaortic-denervated rats present rhythmic contractions. Moreover, drugs that impaired intracellular Ca(2+) release from sarcoplasmic reticulum interrupted the oscillations. The oscillations also depend on the extracellular Ca(2+) entry through L-type Ca(2+).

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Amiloride; Animals; Aorta, Thoracic; Autonomic Denervation; Blood Pressure; Boron Compounds; Calcium Channel Agonists; Calcium Channel Blockers; Calcium Channels, L-Type; Calcium Signaling; Chloride Channels; Dose-Response Relationship, Drug; Inositol 1,4,5-Trisphosphate Receptors; Male; Membrane Transport Modulators; Nitrobenzoates; Periodicity; Phenylephrine; Rats; Rats, Wistar; Ryanodine; Ryanodine Receptor Calcium Release Channel; Sarcoplasmic Reticulum; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Sodium Channel Blockers; Sodium-Calcium Exchanger; Thapsigargin; Time Factors; Vasoconstriction; Vasoconstrictor Agents; Verapamil

The effect of the Cl- channel blockers niflumic acid (NFA), 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), and anthracene-9-carboxylic acid (A-9-C), on Ca2+ signalling in rat pulmonary artery smooth muscle cells was examined. Intracellular Ca2+ concentration ([Ca2+]i) was monitored with either fura-2 or fluo-4, and caffeine was used to activate the ryanodine receptor, thereby releasing Ca2+ from the sarcoplasmic reticulum (SR). NFA and NPPB significantly increased basal [Ca2+]i and attenuated the caffeine-induced increase in [Ca2+]i. These Cl- channel blockers also increased the half-time (t1/2) to peak for the caffeine-induced [Ca2+]i transient, and slowed the removal of Ca2+ from the cytosol following application of caffeine. Since DIDS and A-9-C were found to adversely affect fura-2 fluorescence, fluo-4 was used to monitor intracellular Ca2+ in studies involving these Cl- channel blockers. Both DIDS and A-9-C increased basal fluo-4 fluorescence, indicating an increase in intracellular Ca2+, and while DIDS had no significant effect on the t1/2 to peak for the caffeine-induced Ca2+ transient, it was significantly increased by A-9-C. In the absence of extracellular Ca2+, NFA significantly increased basal [Ca2+]i, suggesting that the release of Ca2+ from an intracellular store was responsible for the observed effect. Depleting the SR with the combination of caffeine and cyclopiazonic acid prevented the increase in basal [Ca2+]i induced by NFA. Additionally, incubating the cells with ryanodine also prevented the increase in basal [Ca2+]i induced by NFA. These data show that Cl- channel blockers have marked effects on Ca2+ signalling in pulmonary artery smooth muscle cells. Furthermore, examination of the NFA-induced increase in [Ca2+]i indicates that it is likely due to Ca2+ release from an intracellular store, most probably the SR.

Topics: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Animals; Anthracenes; Caffeine; Calcium; Calcium Signaling; Cells, Cultured; Chloride Channels; Male; Muscle, Smooth, Vascular; Niflumic Acid; Nitrobenzoates; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Ryanodine; Sarcoplasmic Reticulum

ATP caused a dose-dependent, receptor-mediated increase in the release of glutamate and aspartate from cultured astrocytes. Using calcium imaging in combination HPLC we found that the increase in intracellular calcium coincided with an increase in glutamate and aspartate release. Competitive antagonists of P(2) receptors blocked the response to ATP. The increase in intracellular calcium and release of glutamate evoked by ATP were not abolished in low Ca(2+)-EGTA saline, suggesting the involvement of intracellular calcium stores. Pre-treatment of glial cultures with an intracellular Ca(2+) chelator abolished the stimulatory effects of ATP. Thapsigargin (1 microM), an inhibitor of Ca(2+)-ATPase from the Ca(2+) pump of internal stores, significantly reduced the calcium transients and the release of aspartate and glutamate evoked by ATP. U73122 (10 microM, a phospholipase C inhibitor, attenuated the ATP-stimulatory effect on calcium transients and blocked ATP-evoked glutamate release in astrocytes. Replacement of extracellular sodium with choline failed to influence ATP-induced glutamate release. Furthermore, inhibition of the glutamate transporters p-chloromercuri-phenylsulfonic acid and Ltrans-pyrolidine-2,4-dicarboxylate failed to impair the ability of ATP to stimulate glutamate release from astrocytes. However, an anion transport inhibitor, furosemide, and a potent Cl(-) channel blocker, 5-nitro-2(3-phenylpropylamino)-benzoate, reduced ATP-induced glutamate release. These results suggest that ATP stimulates excitatory amino acid release from astrocytes via a calcium-dependent anion-transport sensitive mechanism.

Topics: 4-Chloromercuribenzenesulfonate; Adenosine Triphosphate; Amino Acid Transport System X-AG; Animals; Aspartic Acid; Astrocytes; ATP-Binding Cassette Transporters; Caffeine; Calcium Signaling; Calcium-Transporting ATPases; Cells, Cultured; Cerebral Cortex; Chelating Agents; Chloride Channels; Chromatography, High Pressure Liquid; Egtazic Acid; Enzyme Inhibitors; Estrenes; Furosemide; Glutamic Acid; Ion Transport; Nitrobenzoates; Phosphatidylinositol Diacylglycerol-Lyase; Pyrrolidinones; Rats; Ryanodine; Sodium; Thapsigargin; Type C Phospholipases