CBF was significantly inhibited by 10 mM phenol (p < 0.01), but not by lower doses, as compared to control CBF (Fig. 3). Washout restored beat frequency to control values. Smoke solutions have phenol concentrations ranging from 284 to 547 |xM (Table 1). The concentrations of phenol in smoke solutions are 17-35 times lower than the concentration needed to inhibit CBF.
Since cyanide was to be introduced to cilia as the potassium salt, a control experiment was first performed in which 100 (jlM KC1 was perfused into culture chambers, and CBF was measured at various times after perfusion. KC1 produced no effect on CBF over a 40-min exposure interval (not shown). In contrast, 50 fxM (p = 0.03) and 100 |лМ (p = 0.0001) of KCN caused a significant decrease in CBF (Fig. 4). Inhibition of beat frequency was also directly observable on the video monitor during the experiments done at 100 |xM KCN. Inhibition of CBF by cyanide was reversed by reintroducing EBSS-H into the culture chamber, and the CBF measured after washing out KCN did not differ significantly from the starting control value (p = 0.65). Lower concentrations of KCN were tested, but they did not significantly alter CBF (not shown). Smoke solutions had concentrations of cyanide ranging from 67 to 167 |aM (Table 1). All of these concentrations are sufficiently high (> 50 |xM) to inhibit CBF.
FIG. 2. The effect of formaldehyde on CBF. CBF is plotted for incubations in control medium (EBSS-H), three concentrations of formaldehyde, and washout medium (EBSS-H). A concentration of 1.66 mM formaldehyde significantly inhibited CBF as compared to control values in EBSS-H alone (p < 0.01). Beat frequency partially recovered by 15 and 30 min after washout but remained significantly lower than in the EBSS-H control group (p < 0.05). Values indicated by * (p < 0.05) and ** (p < 0.01) are significantly lower than the EBSS-H control. Each bar is the mean ± SD of four experiments.
FIG. 3. The effect of phenol on CBF. CBF is plotted for incubations done in control medium (EBSS-H), four concentrations of phenol, and washout medium (EBSS-H). A concentration of 10 mM phenol significantly inhibited CBF as compared to control values in EBSS-H alone (p < 0.01). Beat frequency recovered to control values rapidly after washout. Values indicated by * (p < 0.05) and ** (p < 0.01) are significantly lower than the EBSS-H control. Each bar is the mean ± SD of four experiments.