Periodische Bildung von cycli‐AMP‐Signalen und Chemotaxis von Dictyostelium‐Zellen

Abstract

AbstractExperimental data on oscillations in aggregating cells of the microorganism Dictyostelium discoideum have recently been reviewed by Gerisch et al. (1979). A mathematical analysis based on these data has been published by Sperb (1979).In summary, cells of Dictyostelium discoideum are able to release cyclic AMP periodically and to respond to the same factor by chemotactic orientation. The oscillations of cAMP generation are based on activity changes of adenylate cyclase. Cyclic AMP receptors on the cell surface are functionally coupled to the oscillating system as evidenced by phase shifts that were induced by small pulses of extracellular cAMP. As an important element of the oscillating system the signal processing from cell surface receptors to the adenylate cyclase has been investigated. This pathway exhibits adaptation resulting in the suppression of responses to constant, elevated concentrations of cAMP. The adequate signal input for adenylate cyclase activation is therefore a change of the extracellular cAMP concentration with time.Oscillations in the absence of detectable changes of intra‐ or extracellular cAMP concentrations raise the question if there is a network in D. discoideum cells that undergoes oscillations without being coupled to adenylate cyclase. Cyclic GMP concentrations oscillate with a slight phase difference in advance of c‐AMP, suggesting that the two nucleotide cyclases are independently activated. Rise of extracellular calcium concentrations exert an inhibitory effect on the intracellular accumulation of both cGMP and cAMP.