Control of the beat cycle of respiratory tract cilia by Ca2+ and cAMP

Beat frequency and the duration of the constituent recovery, effective, and rest phases of the beat cycle of respiratory tract cilia were measured photoelectronically before and after manipulation with ionomycin or isoproterenol. Both ionomycin, acting by increasing intracellular Ca2+, and isoproterenol, acting by elevating intracellular adenosine 3',5'-cyclic monophosphate (cAMP), increased beat frequency by reducing the duration of the three phases of the ciliary beat cycle in a similar manner. The addition of increasing concentrations of ATP to ciliated cells permeabilized by exposure to saponin caused a pattern of phase reduction indistinguishable from that observed in whole cells. The beat frequency of permeabilized cells was slower than that of whole cells and insensitive to changes in Ca2+ and cAMP. Ca2+ and cAMP may regulate ciliary beat frequency by acting at a common site within intact cells, possibly regulating the rate at which the axoneme can use ATP or the availability of ATP to the axoneme.