EFFECTS OF POLYAMINES ON INTRACELLULAR CALCIUM AND MECHANICAL-ACTIVITY IN SMOOTH-MUSCLE OF GUINEA-PIG TAENIA-COLI

The effects of the polyamines putrescine, spermidine and spermine on t he mechanical activity in smooth muscle from guinea-pig taenia coli we re investigated. Tissue concentrations of spermidine and spermine were about 240 and 160 nmol g-1, respectively, while the putrescine concen tration was much lower (4 nmol g-1). Intracellular [Ca2+] was determin ed using the Fura-2 method and the effects of extracellularly applied polyamines were observed. Spermine (10(-5)-10(-3) mol l-1) dose-depend ently inhibited spontaneous contractions as well as contractions induc ed by 20-25 mmol l-1 KCl, with 10(-3) mol l-1 spermine giving nearly t otal relaxation. Spermidine (10(-3) mol l-1) relaxed a 20 mmol l-1 KCl contracture, while putrescine had no effect. A decrease in intracellu lar [Ca2+] accompanied the relaxation induced by spermine. In contrast to the effects on spontaneous activity and intermediate [KCl], both t he contraction and the accompanying increase in intracellular [Ca2+] i nduced by 90-120 mmol l-1 KCl were unaffected by spermine. Spermine di d not affect the maximal Ca2+-induced force of chemically skinned taen ia coli preparations, but a small potentiating effect on the Ca2+ sens itivity was observed. The results indicate that the relaxation induced by spermine depends on an intact cell membrane. Furthermore, the rela xing effect is due to decreased intracellular [Ca2+] and seems to occu r only when the contraction is elicited by repetitive action potential s, and not by sustained depolarization.