Calcium-induced calcium release mechanism in guinea pig taenia caeci.

Abstract

Fura-2 was used to measure the amount of Ca released from the intracellular Ca store of a saponin-skinned smooth muscle fiber bundle of the guinea pig taenia caeci (width, 150-250 #m) placed in a capillary cuvette at 20-22~ The amount of Ca actively loaded into the store was assayed when released by the application of 50 mM caffeine and/or 10 #M inositol 1,4,5-trisphosphate (IPs) in the absence of ATP, and was found to have a biphasic dependence on the loading [Ca ~+] with a peak near pCa 6. After Ca loading at pCa 6, IPs released almost all the releasable Ca, whereas caffeine discharged Ca from only -40% of the store. The maximum amount of Ca in the store was some 220 #mol/liter cell water. Ca in the caffeine-releasable store was released approximately exponentially to zero with time when Ca~+ was applied in the absence of ATP, and the rate constant of the Ca-induced Ca release (CICR) increased steeply with the concentration of Ca 2+ applied. Increase in [Mg ~+] (0.5-5.0 mM) or decrease in pH (7.3-6.7) shifted the relation between pCa and the rate of CICR roughly in parallel toward the lower pCa. An adenine nucleotide increased the rate of the CICR, but it did not change the range of effective [Ca~+]. 5 mM caffeine greatly enhanced the CICR mechanism, making it ~30 times more sensitive to [Ca~+]. However the drug had no Ca-releasing action in the absence of Ca ~+. Procaine in millimolar concentrations inhibited the rate of the CICR. These properties are similar to those of the skeletal muscle CICR and ryanodine receptor channels. Rates of the CICR under a physiological ionic milieu were estimated from the results, and a [Ca ~+] >1 #M was expected to be necessary for the activation of the Ca release. This Ca sensitivity seems too low for the CICR mechanism to play a primary physiological role in Ca mobilization, unless assisted by other mechanisms. INTRODUCTIONCaffeine causes transient contractures of smooth muscle bundles in the absence of extracellular calcium ions Bond et al., 1984). In skinned smooth muscle fiber bundles, caffeine initiates transient tension development due to Ca 2+ mobilized within the cells Itoh et al., 1981;Saida, 1982). Release of Ca ~+ from skinned cells by the drug has been directly measured either by radioactive Ca isotope (Stout and Diecke, 1983; Yamaoto and van Breemen, 1985) or by a Address reprint requests to Dr. Masamitsu Iino,

Properties of Ca2+ release induced by clofibric acid from the sarcoplasmic reticulum of mouse skeletal muscle fibres

“…Details of the method are described elsewhere (Iino, 1989;Ikemoto et al, 1995;1996). Brie¯y, thin bundles ®xed in a capillary cuvette were mounted on the stage of a microscope (BHS-RFK, Olympus, Tokyo, Japan) equipped with a¯uorometer (CAM-200, Nihon Bunko Kogyo, Tokyo, Japan) for the measurement of the¯uorescence intensity of Fura-2 at 510 nm with alternating 340 and 380 nm excitations.…”

Functional and Morphological Features of Skeletal Muscle from Mutant Mice Lacking Both Type 1 and Type 3 Ryanodine Receptors

“…The Ca¥ released from the permeabilized fibres was quantified using fura_2 (Grynkiewicz, Poenie & Tsien, 1985). Further details of the method are described elsewhere (Iino, 1989). Briefly, thin bundles were mounted in a capillary cuvette.…”

“…The cuvette was mounted on the stage of a microscope (BHS-RFK, Olympus, Tokyo) equipped with a fluorometer (CAM-200, Nihon Bunko Kogyo, Tokyo) for the measurement of the fluorescence intensity of fura_2 at 510 nm with alternating 340 and 380 nm excitations at room temperature (21-23°C). The SR of permeabilized fibres was actively loaded with Ca¥ for 120 s in a loading solution containing 0·2 ìÒ Ca¥ buffered with 10 mÒ EGTA and 4 mÒ MgATP (Iino, 1989), and then the experimental solution was changed to one not containing Ca¥ and MgATP. Finally, a Ca¥ releasing stimulus was applied in the presence of 35 ìÒ fura_2.…”

Resveratrol Inhibits Nicotinic Stimulation-Evoked Catecholamine Release from the Adrenal Medulla

“…This indicates that the resveratrol has an inhibitory effect on the release of Ca 2＋ from the intracellular pools induced by stimulation of muscarinic ACh receptors, which is weakly responsible for the secretion of CA. It has been shown that Ca 2＋ -uptake into intracellular storage sites susceptible to caffeine (Ilno, 1989) is almost completely abolished by treatment with cyclopiazonic acid during the proceeding of Ca 2＋ load (Suzuki et al, 1992). This is consistent with the findings obtained in exposed smooth muscle fibers of the longitudinal layer of the guinea-pig ileum, where Ca 2＋ -uptake was also inhibited by cylopiazonic acid (Uyama et al, 1992).…”