Fig. 6. Current voltage curves of IP₃-activated Ca²⁺ channels in N. crassa membranes. Current-voltage measurements reveal two distinct Ca²⁺channels: a small conductance channel (circles) and a large conductance channel (triangles). The current is recorded at different membrane potentials, then the voltage dependence of channel current is used to obtain current-voltage relations. Conductance and reversal potential are determined by linear regression. The calculated Nernst potential for Ca²⁺ is -33 mV for 100 µM Ca(OH)₂ (calculated activity of 96 µM) in trans and 1 mM CaCl₂ (calculated activity 7.09 µM) in the cis compartment. Note the difference in scale for small (left) and large (right) conductance channels. In this example, the channel conductance determined from the slope of current-voltages curves was 13 pS for the small channel and 111 pS for the large channel. Amplitude versus voltage was linear and reversed near -25 mV for the small channel and -16 mV for the large channel. Compiled data are presented in Table 3.

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