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K.L. Blair, T.A. Day, M.L. Lewis, J.L. Bennett and R.A. Pax
Parasitology 102:251-258.
Muscle cells from adult male Schistosoma mansoni have
been isolated using a combination of papain digestions and mechanical
dissociation procedures, The muscle fibres isolated in this way
lacked nuclei but they did contract and relax in response to high
[K+], a response which was blocked in the presence of Co2+. From
this we conclude that the isolation procedure yields viable muscle
fibres useful for physiological studies. Patch-clamp recordings
taken from the isolated fibres show a variety of discrete ionic
conductances. In inside-out patches one prominent channel was
a Ca2+-activated K+ channel with a conductance of 195 pS and a
selectivity greater than 10:1 for K+ over Na+, Cs+ or NH4+. Percentage
open time was dependent on [Ca2+] at the intracellular face. With
[Ca2+] at 1 uM or greater, percentage open time was > 95%;
at 0.1 uM it was < 2%. No voltage sensitivity could be detected
in the voltage range from -50 to -10mV membrane potential. Ba2+
(10 mM), but neither tetraethylammoniium nor 3,4-diaminopyridine
blocked the channel from the intracellular face. This Ca2+-activated
K+ channel in the muscle membrane of this acoelomate animal is
similar in most respects to the maxi-K+ channels which have been
described in a variety of cells from more highly evolved animals.