merits, together with previous patch-clamp results, 
indicate the presence of channels in the plasma 
membrane of L. pictus sea urchin sperm. 
A cAMP-Dependent Protein Kinase Associated 
with the Sea Urchin Sperm Plasma Membrane 
Cell motility and the AR are accompanied by an 
increased cyclic nucleotide metabolism and protein 
phosphorylation. Early studies with isolated plasma 
membranes from L. pictus and Arabacia punctu- 
lata invoked a cGMP-dependent protein kinase in 
the OTP and egg peptide (speract- and resact-) de- 
pendent phosphorylation of several membrane poly- 
peptides. However, the nature of the interaction be- 
tween the kinase and the membrane was not 
explored. 
Isolated flagellar plasma membranes from S. pur- 
puratus sea urchin sperm incubated with [7-^^P]ATP 
in the presence of 1 pM cAMP showed an increased 
phosphorylation in several polypeptides. Half- 
maximal response was seen at 0.6 cAMP, while 
much higher cGMP concentrations (100 ixM) were 
required to detect a similar protein phosphoryla- 
tion. Most (80%) of the cAMP-stimulated protein ki- 
nase was resistant to extraction by 1 0 mM EGTA and 
sonication. In contrast, all the activity was recov- 
ered in a detergent-solubilized fraction. 
Membranes pretreated with 200 pM cAMP, ultra- 
centrifuged, and resuspended in buffer solution did 
not undergo cAMP-stimulated phosphorylation in 
their polypeptides. Therefore the cAMP-dependent 
protein kinase appears to be bound to the flagellar 
plasma membranes isolated from S. purpuratus sea 
urchin sperm via its regulatory subunit. This kinase 
has also been detected in isolated sperm head mem- 
branes and may participate in motility and the AR. 
Swollen Sea Urchin Sperm: A New Model 
to Study the Role of Ionic Channels 
in the Response to Egg Factors 
Sea urchin sperm are very tiny cells; the head di- 
ameter is ~2 txm. This has precluded a careful char- 
acterization of their electrophysiological properties 
that would shed light on the molecular mechanisms 
that determine the fascinating egg-induced behav- 
ioral changes. Recently, in collaboration with Drs. 
Donner Babcock and Martha Bosma (University of 
Washington, Seattle), it was found that one can hy- 
potonically swell sea urchin sperm. The swollen 
cells are spherical (~4 ^im in diameter), immotile, 
and metabolically active; and they can respond to 
speract as normal cells do, with changes in mem- 
brane potential, [Ca^^];, and pHj. Swollen sperm can 
be reproducibly patch-clamped, and single chan- 
nels can be recorded. Speract at pM concentrations 
activates a small cation channel. 
Dr. Darszon is Professor of Biochemistry at the 
Biotechnology Institute, National Autonomous 
University of Mexico, Cuernavaca, and Adjunct 
Professor of Biochemistry at the Center for Re- 
search and Advanced Studies, National Polytech- 
nic Institute, Mexico City. 
Article 
Garcia-Soto, J., Araiza, L.M., Barrios, M., Darszon, 
A., and Luna-Arias, J. P. 1991 • Endogenous activity 
of cyclic nucleotide-dependent protein kinase in 
plasma membranes isolated from Strongylocen- 
trotus purpuratus sea urchin sperm. Biochem 
Biophys Res Commun 180:1436-1445. 
EXPLOITATION OF HOST SIGNAL TRANSDUCTION PATHWAYS BY PATHOGENIC BACTERIA 
B. Brett Finlay, Ph.D., International Research Scholar 
Many pathogenic bacteria that cause disease es- 
tablish intimate relationships with host cells. These 
range from adherence to tissue cells to entry into 
host cells and intracellular replication (also known 
as intracellular parasitism) . It is becoming increas- 
ingly apparent that pathogenic microbes are able to 
exploit several host cell functions, including signal 
transduction pathways and cytoskeletal functions. 
and that such exploitations are required for the es- 
tablishment of disease. 
Enteropathogenic Escherichia coli (EPEC) 
Triggers Cytoskeletal Rearrangement 
and Host Protein-Tyrosine Phosphorylation 
EPEC is a major cause of pediatric diarrhea, espe- 
cially in developing nations. However, the mecha- 
506 
