Studies on muscle cells isolated from Schistosoma mansoni: a Ca(2+)-dependent K+ channel.
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 Ca(2+)-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 microM or greater percentage open time was greater than 95%; at 0.1 microM it was less than 2%. No voltage sensitivity could be detected in the voltage range from -50 to -10 mV membrane potential. Ba2+ (10 mM), but neither tetraethylammonium nor 3,4-diaminopyridine blocked the channel from the intracellular face. This Ca(2+)-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.
Blair
K L
KL
Department of Zoology, Michigan State University, East Lansing 48824.
Day
T A
TA
Lewis
M C
MC
Bennett
J L
JL
Pax
R A
RA
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D046508:Culture Techniques; D004553:Electric Conductivity; D008297:Male; D008564:Membrane Potentials; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects*; D012413:Rubidium / Q000494:pharmacology; D012550:Schistosoma mansoni / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure; D012965:Sodium Chloride / Q000494:pharmacology
D015221:Potassium Channels; D012965:Sodium Chloride; D012413:Rubidium; D011188:Potassium; D002118:Calcium