Electrical stimulation and amino acid and ammonia metabolism in the canine gastrocnemius muscle
MacLean, D.A.; Barclay, J.K.; Graham, T.E.
American Journal of Physiology 268(3 Pt 2): R759-R770
1995
ISSN/ISBN: 0002-9513 PMID: 7900920 Document Number: 446855
This study examined the effects of electrical stimulation on amino acid and ammonia (NH-3) metabolism in the isolated in situ canine gastrocnemius muscle preparation. Cut sciatic nerves of 10 mongrel dogs were stimulated at either 3 or 5 twitches/s (10 V, 0.2-ms duration) for 60 min. Muscle NH-3 release dramatically increased on stimulation, and over 60 min the 3- and 5-Hz groups released 86.7 +- 24.2 vs. 160.8 +- 17.4 mu-mol cntdot min-1 cntdot 100 g-1 (P lt 0.05) of NH-3, respectively. Similarly, the intramuscular NH-3 concentration was elevated (P lt 0.05) above rest for both groups throughout stimulation, and it was higher (P lt 0.05) at 5 min for the 5-Hz (82.7 +- 2.4 mu-mol/100 g wet wt) than for the 3-Hz (67.4 +- 7.4 mu-mol/100 g wet wt) group. Stimulation was also characterized by a large release of amino acids by both groups. The total amino acid release for 60 min was 415.4 +- 64.9 vs. 193.3 +- 56.2 (P lt 0.05) mu-mol/100 g for the 3- and 5-Hz groups, respectively. However, there were no shifts or differences between groups in the intramuscular total amino acid pools. Glutamine (Gln) and alanine (Ala) dominated the amino acids released by muscle and together represented 35 and 46% of the total amino acids released over 60 min for the 3- and 5-Hz groups, respectively. The total release of Gln was higher (P lt 0.05) for the 3-Hz (81.1 +- 5.6 mu-mol/100 g) than for the 5-Hz (49.4 +- 10.7 mu-mol/100 g) group, but there were no differences between groups in total Ala release. In contrast, both groups demonstrated an uptake of branched-chain amino acids (valine, isoleucine, and leucine) after 45 min of stimulation. These data show a stimulation-dependent production of NH-3 and release of amino acid by the canine gastrocnemius muscle. These data further show that the degree of net muscle NH-3 production is proportional to the frequency, whereas the degree of amino acid release is an inverse function of frequency.