Differential sensitivity to calciseptine of L-type Ca2+currents in a 'lower' vertebrate (Scyliorhinus canicula), a protochordate (Branchiostoma lanceolatum) and an invertebrate (Alloteuthis subulata)

Voltage-dependent calcium currents in vertebrate (Scyliorhinus canicula), protochordate (Branchiostoma lanceolatum), and invertebrate (Alloteuthis subulata) skeletal and striated muscle were examined under whole-cell voltage clamp. Nifedipine (10 mum) suppressed and cobalt (5 mm) blocked striated/skeletal muscle calcium currents in all of the animals examined, confirming that they are of the L-type class. Calciseptine, a specific blocker of vertebrate cardiac muscle and neuronal L-type calcium currents, was applied (0.2 mum) under whole-cell voltage clamp. Protochordate and invertebrate striated muscle L-type calcium currents were suppressed while up to 4 mum calciseptine had no effect on dogfish skeletal muscle 1,type calcium currents. Our results demonstrate the presence of at least two sub-types of L-type calcium current in these different animals, which may be distinguished by their calciseptine sensitivity. We conclude that the invertebrate and protochordate L-type current sub-type that we have examined has properties in common with vertebrate 'cardiac' and 'neuronal' current sub-types, but not the skeletal muscle sub-type of the L-type channel.