Figure 6. A reduction in [Na⁺]_o slows conduction velocity and enhances the threshold for orthodromic spike generation.

A, somal action potential activity following a current stimulus delivered to the carotid body. Each sweep is an average of 20 trials and is shown with increasing stimulus intensity. A 40 % reduction in [Na⁺]_o slowed conduction time from 4.00 to 5.10 ms. Both records were recorded at the same gain. B, the ordinate is the negative voltage deflection of the evoked spike as a function of stimulus intensity. In this case, a reduction in [Na⁺]_o by 40 % (▵) caused an increase in threshold current of approximately 12 % (5/40 μA) compared with control (○).