Single channel Ca²⁺ currents inHelix pomatia neurons

Abstract

Unitary Ca²⁺ currents of TEA injected Helix neurons were recorded in the “Giga seal” situation (6, 7) from microscopic membrane patches exposed to 50 mM [Ca²⁺]_o, O [Na⁺]_o, 20 mM [TEA⁺]_o and 2.5 μM [TTX]_o. Constant field assumptions yield a channel permeability of 2.9±1.0×10⁻¹⁴ cm³s⁻¹ corresponding to slope conductances of 5 to 15 pS between 0 and −30 mV. Frequency of occurrence of the units strongly increased with depolarization. Mean open time of the Ca²⁺ channels was about 3 ms without obvious dependence on voltage. A similar open time was seen with [Ba²⁺]_o, yielding about double the current strength when compared with [Ca²⁺]_o.