Figure 2.

Effects of osmotic challenges on diffusion curves

A, challenge with 150 mosmol kg⁻¹ ACSF. Sequence of four control diffusion records in 305 mosmol kg⁻¹ medium followed by four in 150 mosmol kg⁻¹ medium and finally four more records after return to 305 mosmol kg⁻¹ medium. Each record consisted of a 10 s baseline followed by the application of the ionophoretic current for 50 s causing the concentration of extracellular TMA⁺ ([TMA⁺]) to increase and then fall after the cessation of the current; the total duration of each individual record was 80 s. The interval between records was longer than that illustrated to permit baseline concentration to stabilise. For all records in A, r = 106 μm, n_t = 0.44. Average results for initial four control records were, λ = 1.67, α = 0.27, k’ = 0.020 s⁻¹; for the curves in hypotonic medium, λ = 1.80, α = 0.10, k’ = 0.016 s⁻¹; for the four records on return to control medium, λ = 1.57, α = 0.34, k’ = 0.015 s⁻¹. B, effect of challenge with 500 mosmol kg⁻¹ ACSF. The experiment was similar to that illustrated in A, except that hypertonic medium was used here. Sequence of four control records in 305 mosmol kg⁻¹ medium followed by four in 500 mosmol kg⁻¹ medium and finally four more records after return to 305 mosmol kg⁻¹ medium. For all records in B, r = 132 μm, n_t = 0.29. Average results for initial four control records were, λ = 1.77, α = 0.20, k’ = 0.024 s⁻¹; for the four curves in hypertonic medium, λ = 1.72, α = 0.37, k’ = 0.018 s⁻¹; for the four records on return to control medium, λ = 1.88, α = 0.13, k’ = 0.017 s⁻¹. In this and the subsequent figure, all concentrations are linear, derived from the ion-selective microelectrode (ISM) calibration. ○, ▪ and ▵ indicate curves shown in Fig. 3.