Journal of Cell Science, Vol 20, Issue 1 1-20, Copyright © 1976 by Company of Biologists

JOURNAL ARTICLES

Critical density for relaying in Dictyostelium discoideum and its relation to phosphodiesterase secretion into the extracellular medium

AR Gingle

The critical cell density for relaying in D. discoideum, N*, has been measured as a function of cell density, N, and time after harvesting, t. It has logarithmic dependence on N for 2.5 X 10(4)/cm2 less than N less than 7.5 X 10(5)/cm2 and saturates for N more than 1.0 X 10(6)/cm2. N* is an increasing function of time after harvesting. The phosphodiesterase (PDE) secretion rate on which N* depends is a constant. Expressions were derived which relate N* to PDE secretion and diffusion. They have been fitted to the data from time delay experiments yielding values of the PDE diffusion constant in 2% buffered agar, Dp + (2.25 +/- 0.15) X 10(-9) cm2/s, and the ratio of relaying threshold concentration to signal pulse size, C*/eta = (1.4 +/- 0.05) X 10(5) cm-3. N* has also been measured in the presence of various amounts of added beef heart PDE. The cAMP relaxation rates, I/tauo, due to beef heart PDE were calculated from the N* measurements and found to be proportional to amounts of added PDE for (I/tauo)max less than (10s-1). Finally, two kinds of inhibition have been observed in the PDE secretion. The PDE activity per cell is constant for N less than 8.0 X 10(4)/cm2, and decreases for larger N. It depends only on N for I/tau less than 10 s-1 and is strongly inhibited by extracellular PDE activity above this relaxation rate.

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