Muscle glutamate

The metabolism of amino acids is complex and is described in standard text books. These are usually converted by aminotransferases to the corresponding 2-oxoacids which are partly oxidized in the matrix of muscle mitochondria and partly exported to the liver. Glutamate and aspartate yield 2-oxoglutarate and oxaloacetate, respectively, which enter the citrate cycle directly, and other 2-... 

Structures of spider toxins that antagonise insect muscle glutamate receptors (and glutamate receptors of other animals)... 

Lai, Y. Y. Siegel, J. M. (1991). Pontomedullary glutamate receptors mediating locomotion and muscle tone suppression. J. Neurosci. 11, 2931-7. 

Avermectin-sensitive sites in A. mum have been identified on pharyngeal muscle (Martin, 1996) using a two-micropipette current-clamp technique (Fig. 21.13A). Glutamate and avermectins produce hyperpolarization and an increase in Cl conductance when either bath-applied or pressure-ejected on to the pharyngeal preparation (Fig. 21.13B,C). These observations establish that one site of action of the avermectins is the pharyngeal muscle of nematodes and that the avermectins can inhibit feeding in nematodes. 

Fig. 21.14. Isolated inside-out patch from pharyngeal muscle with a patch potential of +50 mV and 800 pM glutamate present in the patch pipette shows the opening of two Glu-CI channels. The addition of 1 pM ivermectin to the bath and thus to the inside of the patch produces (in the same patch) opening of up to three Glu-CI channels simultaneously. Ivermectin increases the probability of opening of Glu-CI channels already opening in the presence of glutamate.

Martin, R.J. (1995) An electrophysiological preparation of Ascaris suum pharyngeal muscle reveals a glutamate-gated chloride channel sensitive to the avermectin analogue milbemycin D. Parasitology 112, 252. 

The biological importance of transamination was confirmed using 15N-labeling experiments (Tannenbaum and Shemin, 1950). 15N-leucine incubated with pig heart muscle gave highly labelled 15N-glutamate, evidence that leucine could be transaminated. Isotope experiments were then extended to the whole range of amino acids. 

The 2-oxoglutarate produced is recycled for transamination or may enter the TCA cycle. The ammonia liberated by oxidative deamination is used to form glutamine (from glutamate, catalysed by glutamine synthase) prior to export from the muscle cell ... 

Summarizing, muscle protein provides a number of compounds which can generate fuel for other tissues, a fact which explains the severe wasting seen in people who are literally starving, as muscle protein is sacrificed to maintain function of the central nervous system in particular. We have also seen how glutamate plays a central role in amino acid metabolism in muscle (Figure 7.20). 

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