POLYAMINES INCREASE CA2-MUSCLE OF GUINEA-PIG ILEUM( SENSITIVITY IN PERMEABILIZED SMOOTH)

The effects of polyamines were investigated in strips of smooth muscle from guinea pig ileum permeabilized with beta-escin (0.005%). Spermin e (1 mM) inhibited transient contractions induced in Ca2+-free medium by carbachol (0.1 mM) and GTP gamma S (0.1 mM) but potentiated respons es to caffeine (20 mM) and D-myo-inositol 1,4,5-trisphosphate (40 mu M ). At high ethylene glycol-bis(beta amino-ethyl ether)-N,N,N',N'-tetra acetic acid concentration (10 mM) and in the presence of A-23187 (10 m u M), force at optimal and suboptimal Ca2+ concentrations was increase d both by spermine and by carbachol. Spermine did not potentiate contr action in Ca2+-free medium or after full thiophosphorylation of the re gulatory 20-kDa myosin light chains but slightly potentiated contracti ons produced by partial thiophosphorylation. Also, spermidine and putr escine, as well as the aminoglycoside antibiotic neomycin, increased s ensitivity to Ca2+, with potency correlating with number of positive c harges. After permeabilization by a high concentration (0.1%) of beta- escin, the sensitivity to Ca2+ was increased by spermine but not by GT P gamma S. In preparations permeabilized by Triton X-100, spermine sli ghtly increased Ca2+ sensitivity but not maximal force. Tissue content s of putrescine, spermidine, and spermine in intact ileum muscle were 8, 98, and 184 nmol/g, respectively. Permeabilization by 0.005 and 0.1 % beta-escin reduced spermine contents by 40 and 53%, respectively. Ef fects of added polyamines in permeabilized preparations may thus refle ct physiological effects of endogenous polyamines modulating contracti on in the intact tissue.