EXTRACELLULAR ATP INDUCES HYPERPOLARIZATION AND MOTILITY STIMULATION OF CILIARY CELLS

Cellular membrane potential and ciliary motility were examined in tiss ue cultures prepared from frog palate and esophagus epithelia. Additio n of micromolar concentrations of extracellular ATP caused membrane hy perpolarization and enhanced the beat frequency. These two effects of ATP were 1) dose dependent, reaching a maximum at 10 mu M ATP; 2) depe ndent on the presence of extracellular Ca2+ or Mg2+; 3) insensitive to inhibitors of voltage-gated calcium channels; 4) abolished after depl eting the intracellular Ca2+ stores with thapsigargin; 5) attenuated b y quinidine (1 mM), Cs+ (5-20 mM), and replacement of extracellular Na + by K+; 6) insensitive to charybdotoxin (5-20 nM), TEA (1-20 mu M), a nd apamin (0.1-1 mu M); 7) independent of initial membrane potential; and 8) unaffected by amiloride. In addition, extracellular ATP induced an appreciable rise in intracellular Ca2+. Addition of thapsigargin c aused an initial enhancement of the ciliary beat frequency and membran e hyperpolarization. These results strongly suggest the involvement of calcium-dependent potassium channels in the response to ATP. The resu lts show that moderate hyperpolarization is closely associated with a sustained enhancement of ciliary beating by extracellular ATP.