Characterization of a palytoxin-induced non-selective cation channel in mouse megakaryocytes.
We used the whole-cell clamp and fura-2 techniques to study the membrane current and intracellular Ca2+ concentration ([Ca2+]i) changes of mouse megakaryocytes in response to palytoxin (PTX), a highly potent marine toxin. At a holding potential of -60 mV, PTX induced a sustained inward current in a dose-dependent manner. The reversal potentials measured in the presence of various extracellular major cations indicated that the PTX-induced channel had a non-selective permeability to alkali metal ions. Although elimination of intracellular Ca2+ had no effect on the PTX-induced current, removal of external Ca2+ inhibited the current activation. During the sustained phase of the PTX-induced current, treatment with ADP activated an additional current. Pretreatment with ouabain, an inhibitor of Na+-K+-ATPase, suppressed the PTX-induced current. During the stable phase of the PTX-induced current, challenge with NiCl2 (5 mM) or 2,4-dichlorobenzamil (DCB, 25 microM), a non-selective cation channel blocker, partially reversed the current. Simultaneous measurement of the membrane current and [Ca2+]i showed that PTX induced the current response without increasing the [Ca2+]i. Taken together, these results indicate that PTX induces a non-selective cation channel in mouse megakaryocytes. This channel is distinct from the ADP-operated channel and is sensitive to ouabain, NiCl2 and DCB.
Ichida
K
K
Department of Veterinary Pharmacology, Faculty of Agriculture, Miyazaki University, Japan.
Ikeda
M
M
Goto
K
K
Ito
K
K
D000178:Acrylamides / Q000494:pharmacology*; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000378:metabolism; D002316:Cardiotonic Agents / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003064:Cnidarian Venoms; D004558:Electric Stimulation; D004594:Electrophysiology; D007202:Indicators and Reagents; D007473:Ion Channels / Q000187:drug effects*; D008297:Male; D008533:Megakaryocytes / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D000095702:Polyether Toxins
D000178:Acrylamides; D000244:Adenosine Diphosphate; D015220:Calcium Channels; D002316:Cardiotonic Agents; D003064:Cnidarian Venoms; D007202:Indicators and Reagents; D007473:Ion Channels; D010042:Ouabain; C010272:palytoxin; D000095702:Polyether Toxins