Ionic mechanisms underlying spontaneous muscle contractions in the liver fluke, Fasciola hepatica.
Spontaneous contractions of liver fluke muscle were abolished in Ca(2+)-free saline and by 100 microM nifedipine and reduced by 5 mM cadmium chloride, suggesting that they are dependent on extracellular Ca(2+). Caffeine (5 mM) significantly increased contraction amplitude and frequency. Ryanodine (100 microM) failed to block the caffeine response but significantly reduced spontaneous contraction frequency, suggesting that intracellular stores have a functional role. Cyclopiazonic acid (5 microM) had no effect on the caffeine response or spontaneous activity. 3-Isobutyl-1-methylxanthine (IBMX), forskolin, and 8-bromoadenosine 3',5'-cyclic monophosphate significantly increased spontaneous contractions, which implies that cAMP has a regulatory function in motility. Caffeine, however, produced no measurable increase in cAMP. The caffeine effect was inhibited by cadmium chloride and nifedipine, whereas IBMX-induced increases in amplitude were reduced by cadmium chloride. Thus caffeine and cAMP appear capable of opening plasma membrane Ca(2+) channels, but the involvement of cAMP in caffeine responses has not been proved.
Graham
M K
MK
School of Biology and Biochemistry, The Queen's University of Belfast, Belfast BT9 7BL, United Kingdom.
McGeown
J G
JG
Fairweather
I
I
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002122:Calcium Chloride / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D005110:Extracellular Space / Q000378:metabolism; D005210:Fasciola hepatica / Q000502:physiology*; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D007477:Ions; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology
D002121:Calcium Channel Blockers; D007477:Ions; D012433:Ryanodine; D012965:Sodium Chloride; D000242:Cyclic AMP; D009543:Nifedipine; D002122:Calcium Chloride; D002118:Calcium