Calcium currents from jellyfish striated muscle cells: preservation of phenotype, characterisation of currents and channel localisation.

When striated muscle cells of the jellyfish Polyorchis penicillatus were dissociated at 30 degrees C they retained their in vivo morphology and the integrity of ionic currents. This contrasted with cells dissociated at room temperature that rarely expressed any inward currents. Whole-cell, patch-clamp recordings from dissociated muscle cells revealed that the inward component of the total ionic current consisted of only one calcium current. This calcium current activated at -70 mV, peaked at -30 mV, and inactivated within 5 ms. In comparison with barium and strontium ions, calcium ions were the preferred current carriers. Calcium channels can be blocked by dihydropyridines and nickel ions at micromolar levels. Several properties of this current are reminiscent of T-type calcium currents. Localisation of this channel using the fluorescent channel blocker fDHP and the fluorescent dye RH414 indicated that myofibres had a higher density of these channels than the somata.