Relaxing effect of spermine and spermidine on intact and glycerol-treated muscle

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Abstract
Spermine and spermidlne are aliphatic poly-amines found in muscle of different animal species. In vitro they induce relaxation of smooth muscle (guinea pig ileum and taenia coli) made to contract by acetylcholie, histamine, nicotine, caffeine, and excess of K. A preparation completely depolarized by KCl-Ringer solution and then made to contract by acetylcholine undergoes complete relaxation in the presence of 3 m[image] spermine or 8 m[image] spermidine. Spermine and spermidine (5.5-14.0 m[image]) also relax frog skeletal muscle (rectus abdominis and sartor ius) contracted either by acetyl-choline, moderate increase in extracellular KC1 concentration (28 m[image]), or electrical stimulation. Unlike smooth muscle, spermine in concentrations of 50 m[image] did not relax rectus abdominis preparations previously depolarized by 95 m[image] K2SO4 and contracted by caffeine. However, preincubation with spermine (50 m[image]) in 95 m[image] K2SO4 inhibits by 50% the contraction induced by a standard concentration of caffeine. Spermine and spermidine in concentrations of 30-50 m[image] also induce relaxation of glycerol-extracted myofibrils contracted by ATP-Mg. This relaxing effect on glycerinated myofibrils is not reversed by excess Ca or Mg ions.