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Response of Dictyostelium plasma membranes to adenosine 3':5'-cyclic monophosphate
Abstract:
Myxamoebae of the cellular slime mold Dicytostelium discoideum aggregate in response to a chemotactic substance identified as adenosine 3':5'-cyclic monophosphate. Upon aggregation cell division is suppressed, the cells become adhesive, and differentiation is initiated. Freeze-fracture studies of myxamoebae were conducted to determine the effect of cyclic AMP and calcium on plasma membrane ultrastructure. The inner surfaces of the plasma membranes exhibited particulate structures whose sizes (43-187 A) and frequency distribution were determined. Cyclic AMP and calcium induced within 2 hr the formation of particles having average diameters 1.7-times and 1.5-times greater, respectively, than those of the vegetative myxamoebae controls. These data suggest that cyclic AMP mobilizes the intracellular calcium which may be effective in changing plasma membrane structure.
Insights
Cellular slime mold cells aggregate using adenosine 3':5'-cyclic monophosphate (cyclic AMP). Cyclic AMP and calcium alter plasma membrane structure by increasing particle size, suggesting cyclic AMP mobilizes calcium to change membrane properties.
Area of Science:
- Cell Biology
- Biochemistry
- Developmental Biology
Background:
- Cellular slime molds like Dictyostelium discoideum aggregate via chemotaxis.
- Adenosine 3 ':5 '-cyclic monophosphate (cyclic AMP) is the key chemoattractant.
- Aggregation triggers cell cycle arrest, adhesion, and differentiation.
Purpose of the Study:
- To investigate the impact of cyclic AMP and calcium on the plasma membrane ultrastructure of D. discoideum myxamoebae.
- To quantify changes in plasma membrane particle size and distribution.
Main Methods:
- Freeze-fracture electron microscopy was employed.
- Analysis of plasma membrane inner surfaces to determine particulate structure size and frequency.
- Comparison between vegetative controls and cells treated with cyclic AMP and calcium.
Main Results:
- Plasma membranes of D. discoideum myxamoebae exhibit particulate structures.
- Exposure to cyclic AMP and calcium for 2 hours significantly increased the average diameter of these particles (1.7-fold and 1.5-fold, respectively).
Conclusions:
- Cyclic AMP and calcium influence the ultrastructure of the D. discoideum plasma membrane.
- These findings suggest cyclic AMP may mobilize intracellular calcium, mediating structural changes in the plasma membrane during aggregation.