Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.13.12.5 (aequorin)
 1,451 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. We used the bioluminescent protein aequorin, which emits light when it combines with Ca2+, to test the hypothesis that the inotropic and lusitropic actions of DPI 201-106 are due to changes in intracellular Ca2+ handling in papillary muscles from ferrets and guinea-pigs. 2. DPI 201-106 increased peak isometric tension (T) in a dose-dependent manner, with an 83% increase in T as the concentration of DPI 201-106 was increased to 1 x 10(-5) M; however, peak [Ca2+]i did not increase significantly until the concentration of DPI 201-106 reached 3 x 10(-6) M, suggesting a sensitization of the contractile apparatus to Ca2+. 3. Tetrodotoxin (1 x 10(-6) M), which did not reduce the tension response significantly before DPI 201-106, decreased both [Ca2+]i and T in the presence of 1 x 10(-5) M DPI 201-106, suggesting involvement of a sodium channel activation mechanism; however, tetrodotoxin did not completely reverse the calcium sensitization. 4. The shift of the [Ca2+]i versus T relationship was not observed in the presence of another sodium channel agonist, veratridine (3 x 10(-7)-1 x 10(-6) M). 5. In the guinea-pig, DPI 201-106 markedly prolonged relaxation of tension (increase of 60% in the time from peak to 50% tension regression), which was accompanied by the appearance of a second component in the aequorin light signal; effects on relaxation were less prominent in the ferret. 6. Tension prolongation and the second component of the [Ca2+]i transient in the guinea-pig were exacerbated by increased [Ca2+]o and decreased by tetrodotoxin. Ryanodine (3 x 10(-7) M) markedly diminished the calcium transient in controls and the initial component of the calcium transient in the presence of DPI 201-106, but had only a modest effect on the second component. 7. We conclude that although sodium agonism plays a role, sensitization of the contractile apparatus to Ca2+ is an important mechanism in the positive inotropic action of DPI 201-106. 8. The negative lusitropic action of DPI 201-106 varies between ferret and guinea-pig, possibly reflecting differences between these two species in subcellular Ca2+ handling.
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PMID:Mechanisms of positive inotropic effects and delayed relaxation produced by DPI 201-106 in mammalian working myocardium: effects on intracellular calcium handling. 274 84

1. Changes in ionized calcium in giant axons were followed by recording the light produced by injected aequorin.2. From the effect of injecting calcium buffers the internal concentration of ionized calcium was found to be about the same as in a mixture of 45 Ca EGTA:55 free EGTA, i.e. about 0.3 muM.3. After an axon had been exposed to cyanide for 50-100 min the velocity of the aequorin reaction increased about 500 times. This effect, which could be reversed rapidly by removing cyanide, was probably brought about by release of calcium from an internal store.4. Injecting 30 mumole ATP per litre of axoplasm into a cyanide-poisoned axon caused a transient lowering of light intensity; oligomycin blocked the effect.5. Raising external calcium or replacing external sodium by choline or lithium reversibly increased the light produced by axons injected with aequorin.6. Stimulation at 50-200 impulses/sec in a solution containing 112 mM-Ca caused the light intensity to increase to a new steady level; after stimulation the light intensity returned to its original level with a time constant of 10-30 sec. Similar but smaller effects were seen in solutions containing less external calcium. The recovery after stimulation is probably due to uptake of calcium by the internal store.7. Injecting 3 m-mole EGTA per litre axoplasm lowered the resting glow and abolished the aequorin response to stimulation.8. There was no light response to stimulation immediately after an axial injection of aequorin and the effect increased to a ;steady' level with a half-time of about 5 min. The conclusion is that the rise in calcium concentration resulting from stimulation is confined to the peripheral part of the axon and that the diffusion coefficient of aequorin in axoplasm is about 4 x 10(-7) cm(2)/sec.9. The increment in light per impulse often increased markedly during the course of a long experiment and there was also considerable variation between axons.10. If the light response to stimulation was small it was proportional to the frequency of stimulation; if large to the square of the frequency.11. Voltage-clamp experiments showed that the calcium entry associated with a depolarizing pulse could be divided into an early component which was abolished by tetrodotoxin (TTX), and a late component which was unaffected by this inhibitor.12. The time relations of the early calcium entry were consistent with its being a leak of calcium ions through the sodium channel; the permeability of the sodium channel to calcium was about 1% of the permeability to sodium.13. The late entry of calcium was little changed by injecting enough tetraethylammonium (TEA) to block the outward potassium current; it was greatly reduced by external concentrations of manganese which had little effect on the maximum potassium conductance.14. The voltage-response curve for the late entry of calcium had a well defined maximum and was similar in shape to the curve relating calcium entry to depolarization at the presynaptic ending (Katz & Miledi, 1969, 1970).
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PMID:Depolarization and calcium entry in squid giant axons. 513 53

Defective regulatory interactions between the cystic fibrosis conductance regulator (CFTR) and the epithelial sodium channel (ENaC) have been implicated in the elevated Na+ transport rates across cystic fibrosis airway epithelium. It has recently been proposed that ENaC downregulation by CFTR depends on the ability of CFTR to conduct Cl- into the cell and is negligible when Cl- flows out of the cell. To study the mechanisms of this downregulation we have measured amiloride-inhibitable Na+ current (Iamil) in oocytes co-expressing rat ENaC and human wild-type CFTR. In oocytes voltage-clamped to -60 mV, stimulating CFTR with 1 mm IBMX reduced Iamil by up to 80%, demonstrating that ENaC is inhibited when Cl- is conducted out of the cell. Decreasing the level of CFTR stimulation in a single oocyte, decreased both the degree of Iamil downregulation and the CFTR-mediated plasma membrane Cl- conductance, suggesting a direct correlation. However, Iamil downregulation was not affected when Cl- flux across oocyte membrane was minimized by holding the oocyte membrane potential near the Cl- reversal potential (67% +/- 10% inhibition at -20 mV compared to 79% +/- 4% at -60 mV) demonstrating that Iamil downregulation was independent of the amount of current flow through CFTR. Studies with the Ca2+-sensitive photoprotein aequorin showed that Ca2+ is not involved in Iamil downregulation by CFTR, although Ca2+ injection into the cytoplasm did inhibit Iamil. These results demonstrate that downregulation of ENaC by CFTR depends on the degree of CFTR stimulation, but does not involve Ca2+ and is independent of the direction and magnitude of Cl- transport across the plasma membrane.
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PMID:Downregulation of epithelial sodium channel (ENaC) by CFTR co-expressed in Xenopus oocytes is independent of Cl- conductance. 1035 64