Calcium current in growth balls from isolated Helix aspersa neuronal growth cones

Growth cones were severed from their neurites in primary cultures of Helix aspersa neurons. Following isolation, growth cones rolled up into 5-10-micron-diameter spheres, which remained attached to a poly-L-lysine or lectin-coated glass coverslip. Whole-cell-configuration patch-clamp recordings from isolated growth cones revealed inward calcium currents upon block of outward currents with internally perfused CsCl. Up to 50 microM tetrodotoxin did not affect this current. In 20-micron-diameter spheres, a peak current of 1.2 nA was reached within 3 ms under voltage-clamp conditions for a 60-mV pulse from a holding potential of -50 mV. Channel density calculations averaged to approximately one channel per square micrometer. A two-phase inactivation was evident under voltage-clamp steps from -50 mV to +15 mV. The growth balls described can be internally perfused and voltage clamped to measure ionic currents involved in growth cone function.