Figure 10.

Voltage-dependent block by internal Mg²⁺ and external Ca²⁺. (A) Voltage dependence induced by internal Mg²⁺. Solutions as in Fig. 7; pipette solutions contained Cs⁺ aspartate with or without Mg²⁺. Ramp I-V trace recorded in the presence of internal Mg²⁺ was divided point by point by an I-V trace obtained in a different cell in the absence of internal Mg²⁺. The smooth line represents a fit to the Boltzmann distribution (Eq. 3). E _h = 20 mV; k = −13 mV. (B) Voltage dependence of Ca²⁺ block. I-V curves with 100 μM [Ca²⁺]_o were divided by I-V curves with 1 μM [Ca²⁺]_o and fitted to a Boltzmann relation. E _h = 20 mV; k = 15 mV.