ATP und Ca2+ induzierte actomyosinartige Kontraktion glycerinisierter Makronuklei

Summary The addition of 2 mM-3 mM ATP to macronuclei ofParamecium bursaria suspended in a glycerol buffer medium causes a decrease in their volume up to 23% within 3 minutes. The infiltration medium must not only contain Ca²⁺, but must also be of low ionic strength for ATP to be effective. A slow, careful exchange of the glycerol medium for the contraction solution is also necessary. Ca²⁺ present alone in the standard contraction buffer can likewise induce a limited volume decrease; in the presence of low concentrations of Ca²⁺, Mg²⁺ shows no detectable effect on glycerinated nuclei. When the nuclear volume has been reduced by ATP in the presence of Ca²⁺, the addition of EGTA induces a reexpansion of the nuclei. Salyrgan, an organic mercurial, either prevents or abolishes the ATP-induced contraction. Other nucleotide triphosphates such as guanosine triphosphate (GTP), inosine triphosphate (ITP) or uridine triphosphate (UTP) likewise induce a volume decrease of the glycerinated macronuclei, but to a distinctly lesser extent than ATP.The results indicate that the volume decrease caused by the ATP-contraction solution is not a passive osmotic process. The resemblance to actomyosin contractions suggests that the volume decrease reported here might also be the result of the reaction of nuclear actomyosin and ATP.