Calcium efflux has been measured from two different fractions of rabbit skeletal muscle partially loaded with calcium oxalate, under conditions in which the inward calcium pump is inoperative. Efflux from the heavy sarcotubular fraction (2000-8000 x g) is stimulated by ryanodine and caffeine, whereas calcium efflux from a light fraction (12000-35000 xg) is much less sensitive to these drugs. Quinidine and chlorpromazine stimulate calcium efflux from both muscle fractions. These effects of ryanodine and caffeine are completely blocked, and those of quinidine and chlorpromazine partially blocked, by 5 mM magnesium, although magnesium does not affect calcium efflux in the absence of drugs. Zinc stimulates and uranyl ion depresses calcium efflux.A number of drugs, including ryanodine [1,2], caffeine [3] and quinidine [4] have been shown to inhibit calcium uptake by sarcotubular fragments when assayed in media containing oxalate, and the assumption has been made that such inhibition is due to effects of these drugs on the ATP-dependent calcium pump, since the presence of oxalate would seem to reduce any concurrent calcium efflux to an extremely low level. However, the possibility remains that these drugs might exert some part of their observed effects on calcium transport by stimulating calcium efflux, rather than solely by inhibiting the inward transport of calcium. It seemed important to establish any effect of the drugs on calcium efflux, since a stimulation of efflux would indicate that the drugs are acting a t some site other than the calcium Pump.Measurements of calcium efflux cannot be made unambiguously in the presence of ATP, due to the activity of the calcium pump, but calcium efflux can be measured in systems in which the sarcotubular vesicles are first partially loaded with calcium oxelate in the presence of a limiting supply of ATP. Under these conditions the energy-dependent inward transport of calcium ceases after the rapid exhaustion of the ATP, and calcium efflux can then be demonstrated, as has been described by Hasselbach [5].The present report describes the effects of a number of drugs and metals on calcium efflux from a heavy sarcotubular fraction of skeletal muscle, isolated between 2000-8000 x g, which exhibits greater sensitivity to ryanodine and to caffeine than do the more widely studied lighter muscle fractions ~3 1 . MATERIALS AND METHODSThe heavy and light muscle fractions were isolated between 2000-8000 ~g a n d 1 2 0 0 0 -3 5 0 0 0~g respectively from a homogenate of rabbit skeletal muscle, as described previously [I]. One modification was made from the original procedure in that the muscle was homogenised in 10 rather than 3 volumes of 100mM KCI to 5 m M histidine a t pH7.4. The fractions were stored in this medium and used within 48 hours. The experiments were started by first partially loading the vesicles with calcium oxalate, by incubating 10 mg protein a t 30" with stirring in 3 ml of uptake medium containg 3 pmoles of CaC1, labelled with 45Ca, 3 pmoles ATP, 6 pmoles EGTA, 150 pm...

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SUMMARY:Washed suspensions of certain bacteria can synthesize alanine from pyruvate and ammonia. This has been studied in detail in Bacillus subtilis. Several other amino acids can be formed from the corresponding keto-acids, but synthesis was most rapid in the case of alanine. Notably, glutamic acid is formed from ketoglutarate relatively slowly, whilst oxalacetate fails to give aspartate. Pyruvate can accept an amino group from a number of amino acids by transamination (but aspartic and glutamic acids are less effective than ammonia itself). It is possible that the reductive amination of pyruvate may proceed directly rather than through transamination from some other primary amino-acceptor.The last step in the synthesis of an amino acid is often the exchange of the carbonyl group of the appropriate keto acid for an amino group. When the ultimate source of the latter is ammonia we can refer to the reaction as

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The effects of carbamazepine, in vitro, on adrenergic neuronal and whole brain synaptosomal uptake and release of tritiated norepinephrine (3H-NE) were assessed. At 10(-4) M, carbamazepine inhibited 3H-NE uptake by 22% in rabbit thoracic aorta and in brain synaptosomes. At the same concentration, carbamazepine inhibited stimulation-induced release of 3H-NE by 42.6% and inhibited isometric contraction in rabbit ear artery helical strips by 31.6%. At 10(-5) M, carbamazepine exhibited a 17.6% inhibition of 3H-NE uptake in brain synaptosomes in the absence of effects on transmitter release. Cocaine, 10(-4) M, and imipramine, 10(-4) M, inhibited uptake by 88% and 85%, respectively, in aorta, and cocaine, 10(-4) M, inhibited synaptosomal uptake by 67.7%. Since antiepileptic blood levels of carbamazepine range between 1.3 and 3.0 X 10(-5) M, it was concluded that the observed effects of carbamazepine are insufficient to account for the anticonvulsant action of the drug. However, the blockade of 3H-NE uptake by brain synaptosomes at 10(-5) M serves to explain the recently described analeptic activity of this agent.