Functional voltage-gated Ca2+ channels in muscle fibers of the platyhelminth Dugesia tigrina.
The presence and function of voltage-gated Ca(2+) channels were examined in individual muscle fibers freshly dispersed from the triclad turbellarian Dugesia tigrina. Individual muscle fibers contracted in response to elevated extracellular K(+) in a concentration-dependent fashion. These depolarization-induced contractions were blocked by extracellular Co(2+) (2.5 mM), suggesting that they were dependent on depolarization-induced Ca(2+) influx across the sarcolemma. A voltage-gated inward current was apparent in whole cell recordings when the outward K(+) current was abolished by replacement of intracellular K(+) by Cs(+). This inward current was amplified with increasing concentration (</=10 mM) of extracellular Ba(2+) and was independent of extracellular Na(+) concentration suggesting the current was mediated by voltage-gated Ca(2+) channels. Further, and supporting the hypothesis that the inward current was mediated by these Ca(2+) channels, the Ba(2+) current was blocked by extracellular Co(2+) (2.5 mM) but not by tetrodotoxin (5 microM). Action potentials were generated by the muscle fibers in the presence of, but not in the absence of, extracellular Ba(2+) (5 mM). These data are the first clear demonstration of a voltage-gated Ca(2+) channel current in platyhelminth muscle, and they demonstrate a role for Ca(2+) influx in depolarization-induced contractions of muscle in these organisms.
Cobbett
Peter
P
Department of Pharmacology and Toxicology, and the Neuroscience Program, Michigan State University, East Lansing, MI 48824-1317, USA. cobbett@msu.edu
Day
Timothy A
TA
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D004553:Electric Conductivity; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D010932:Planarians / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism
D015220:Calcium Channels; D015221:Potassium Channels; D015222:Sodium Channels; D012964:Sodium; D011188:Potassium; D002118:Calcium