Chlamydomonas contains calcium stores that are mobilized when phospholipase C is activated.
Mastoparan induces Ca(2+)-dependent deflagellation of the unicellular green alga Chlamydomonas moewusii Gerloff, as well as the activation of phospholipase C and the production of inositol 1,4, 5-trisphosphate (InsP(3); T. Munnik et al., 1998, Planta 207: 133-145). Even in the absence of extracellular Ca(2+), mastoparan still induces deflagellation (L.M. Quarmby and H.C. Hartzell, 1994, J Cell Biol 124: 807-815; J.A.J. van Himbergen et al., 1999, J Exp Bot, in press) suggesting that InsP(3) mediates Ca(2+) release from intracellular stores. To test this hypothesis, cells were pre-loaded with (45)Ca(2+) and their plasma membranes permeabilized by digitonin. Subsequent treatment of the cells with mastoparan (3.5 microM) induced release of intracellular (45)Ca(2+). Mastoparan also activated phospholipase C in permeabilized cells, as demonstrated by the breakdown of (32)P-phosphatidylinositol 4,5-bisphosphate and the production of diacylglycerol. The mastoparan analogues mas7 and mas17 were also effective and their efficacy was correlated with their biological activity. X-ray microanalysis showed that electron-dense bodies (EDBs) are a major Ca(2+) store in C. moewusii. Analysis of digitonin-permeabilized cells showed that EDBs lost calcium at digitonin concentrations that released radioactivity from (45)Ca(2+)-labelled cells, suggesting that (45)Ca(2+) monitored the content of EDBs. X-ray microanaysis of living cells treated with mastoparan also revealed that calcium was released from EDBs.
Kuin
H
H
Institute for Molecular Cell Biology, BioCentrum Amsterdam, University of Amsterdam, Kruislaan 318, 1098 SM Amsterdam, The Netherlands.
Koerten
H
H
Ghijsen
W E
WE
Munnik
T
T
van den Ende
H
H
Musgrave
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D002132:Calcium Radioisotopes; D002696:Chlamydomonas / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004072:Digitonin; D004789:Enzyme Activation; D036341:Intercellular Signaling Peptides and Proteins; D008854:Microscopy, Electron; D010455:Peptides; D010539:Permeability; D010738:Type C Phospholipases / Q000378:metabolism*; D014862:Wasp Venoms / Q000494:pharmacology
D002132:Calcium Radioisotopes; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D014862:Wasp Venoms; C037500:mastoparan; D010738:Type C Phospholipases; D004072:Digitonin; D002118:Calcium