Role of calcium influx through voltage-operated calcium channels and of calcium mobilization in the physiology of Schistosoma mansoni muscle contractions.
We tested the hypothesis that voltage-operated Ca2+ channels mediate an extracellular Ca2+ influx in muscle fibres from the human parasite Schistosoma mansoni and, along with Ca2+ mobilization from the sarcoplasmic reticulum, contribute to muscle contraction. Indeed, whole-cell voltage clamp revealed voltage-gated inward currents carried by divalent ions with a peak current elicited by steps to +20 mV (from a holding potential of -70 mV). Depolarization of the fibres by elevated extracellular K+ elicited contractions that were completely dependent on extracellular Ca2+ and inhibited by nicardipine (half inhibition at 4.1 microM). However these contractions were not very sensitive to other classical blockers of voltage-gated Ca2+ channels, indicating that the schistosome muscle channels have an atypical pharmacology when compared to their mammalian counterparts. Futhermore, the contraction induced by 5 mM caffeine was inhibited after depletion of the sarcoplasmic reticulum either with thapsigargin (10 microM) or ryanodine (10 microM). These data suggest that voltage-operated Ca2+ channels do contribute to S. mansoni contraction as does the mobilization of stored Ca2+, despite the small volume of sarcoplasmic reticulum in schistosome smooth muscles.
Departamento de Farmacologia Básica e Clínica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Brazil.
D L
DL
Mendonça-Silva
E
E
Novozhilova
P J R
PJ
Cobbett
C L M
CL
Silva
F
F
Noël
M I J
MI
Totten
A G
AG
Maule
T A
TA
Day
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology*; D004594:Electrophysiology; D008564:Membrane Potentials; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D012433:Ryanodine / Q000494:pharmacology; D012550:Schistosoma mansoni / Q000378:metabolism / Q000502:physiology*; D019284:Thapsigargin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D012433:Ryanodine; D002110:Caffeine; D019284:Thapsigargin; D002118:Calcium