Figure 7.

Effects of free fatty acids on K_ACh channel activity and open time constants. Membrane potential was held at −60 mV. (A) To inside-out patches containing ATP-modified K_ACh channels, a lipid was added at increasing concentrations (0–5 μM). Relative channel activity was determined at each lipid concentration. Data were fitted to the Hill equation nP _o = {0.9/[1 + ([FA/K _d]^N)] + 0.1}, where FA is the lipid species, K _d is concentration at which half maximal inhibition occurs, and N is the Hill coefficient (1.8–2.2). Lipid fraction of the cytosol was also tested at different dilutions. Undiluted original cytosolic lipid was prepared by adding 1 ml of bath solution to dried lipids obtained from 1 ml of CF (20 mg protein/ml), and corresponds to the 100 μM free fatty acid on the x scale. (B) Open time constants calculated from transition rates obtained after fitting the data to the two kinetic schemes shown in Fig. 2 B. Each bar is the mean ± SD of four determinations. *Significant difference from the value determined in the absence of ATP.