Identification of the Ca2+ conductance responsible for K+-induced backward swimming in Paramecium caudatum.
Membrane potential responses of Paramecium caudatum to an application of K+-rich solution were examined to understand the mechanisms underlying K+-induced backward swimming. A wild-type cell impaled by a microelectrode produced action potentials followed by a sustained depolarization in response to an application of a K+-rich test solution. After termination of the application, a prolongation of the depolarization (depolarizing after-potential) took place. Behavioral mutants incapable of exhibiting K+-induced backward swimming did not show depolarizing afterpotentials. Upon short application of K+-rich solution, the timing and duration of the ciliary reversal of the wild-type cell coincided well with the K+-induced depolarization. The duration of the depolarizing afterpotential decreased as the duration of the application increased. The depolarizing afterpotential recovered slowly after it had been suppressed by a preceding application of the K+-rich solution. By injection of an outward current into the wild-type cell, the action potentials were evoked normally during the period when the K+-induced depolarizing afterpotential was suppressed. We concluded that the prolongation of the depolarizing membrane potential response following the application of the K+-rich solution represents the Ca2+ conductance responsible for the K+-induced backward swimming in P. caudatum and that the characteristics of the K+-induced Ca2+ conductance are distinct from those of the Ca2+ conductance responsible for the action potentials.
Oami
K
K
Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan. oami@sakura.cc.tsukuba.ac.jp
Takahashi
M
M
D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D002628:Chemoreceptor Cells; D004305:Dose-Response Relationship, Drug; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology*; D009154:Mutation; D010247:Paramecium / Q000187:drug effects* / Q000502:physiology*; D011188:Potassium / Q000008:administration & dosage*; D013550:Swimming / Q000502:physiology*
D015220:Calcium Channels; D011188:Potassium