Roles of Adenylate Cyclases in Ciliary Responses of Paramecium to Mechanical Stimulation

Paramecium shows rapid forward swimming due to increased beat frequency of cilia in normal (forward swimming) direction in response to various kinds of stimuli applied to the cell surface that cause K⁺ -outflow accompanied by a membrane hyperpolarization. Some adenylate cyclases are known to be functional K⁺ channels in the membrane. Using gene-specific knockdown methods, we examined nine paralogues of adenylate cyclases in P. tetraurelia to ascertain whether and how they are involved in the mechanical stimulus-induced hyperpolarization-coupled acceleration of forward swimming. Results demonstrated that knockdown of the adenylate cyclase 1 (ac1)-gene and 2 (ac2)-gene inhibited the acceleration of forward swimming in response to mechanical stimulation of the cell, whereas that spared the acceleration response to external application of 8-Br-cAMP and dilution of extracellular [K⁺ ] induced hyperpolarization. Electrophysiological examination of the knockdown cells revealed that the hyperpolarization-activated inward K⁺ current is smaller than that of a normal cell. Our results suggest that AC1 and AC2 are involved in the mechanical stimulus-induced acceleration of ciliary beat in Paramecium.