Spatial distribution of channels greatly influences the current predicted by the model. (*A*) Four modeled channel distributions. The blue line shows a uniform distribution. The others show narrow bands centered at 3 *μ*m, near the base of the cilium (*green*); 24 *μ*m (*black*); or 65 *μ*m, near the distal tip of the cilium (*red*). The distribution shown in black most closely represents the experimental results (e.g., ). In all cases, 1890 channels were placed on a 70-*μ*m cilium. (*B*) The predicted current as a function of time for each of the modeled channel distributions assuming the cilium was placed in a bath containing 20 *μ*M cAMP. Current amplitudes at infinite time were −401 pA (*green*), −161 pA (*blue*), −114 pA (*black*), and −47 pA (*red*). In the absence of cable-conduction loss, the 1890 channels would produce a total current of −541 pA at −50 mV. The smaller plateau values were due to this loss, which is greater as the channels are placed near the distal tip. The times to reach 50% of the plateau current were 8 ms (*green*), 76 ms (*blue*), 252 ms (*black*), and 1.26 s (*red*). (*C*) Effects of varying the assumed number of cAMP-binding sites per channel. From left to right, the predicted currents are shown when 0, 1, 2, 3, or 4 binding sites per channel were assumed. The second curve from the left (one binding site) is the same as the black curve in *B*. Times to reach 50% of the plateau current ranged from 192 to 376 ms. In all cases, the plateau current was −114 pA. (*D*) Effects of assuming a uniform, constant diameter equal to the diameter of the proximal segment (0.28 *μ*m, *lower curve*) or the distal segment (0.19 *μ*m, *higher curve*). The lower curve is the same as the black curve in *B*. Current amplitudes reached −114 pA (0.28 *μ*m) or −59 pA (0.19 *μ*m). Times to reach 50% of the plateau current were 252 ms (0.28 *μ*m) and 243 ms (0.19 *μ*m).

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