Antibodies to the ciliary membrane of Paramecium tetraurelia alter membrane excitability.

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Abstract
Immobilization of Paramecium followed the binding of antibodies to the major proteins of the ciliary membrane (the immobilization antigens, i-antigens, .apprx. 250,000 MW). Immunoelectron microscopy showed this binding to be serotype-specific and to occur over the entire cell surface. Antibody binding also reduced the current through the Ca-channel of the excitable ciliary membrane as monitored using a voltage-clamp. The residual Ca-current appeared normal in its voltage sensitivity and kinetics. As a secondary consequence of antibody binding, the Ca-induced K-current was also reduced. The resting membrane characateristics and other activatable currents, however, were not significantly altered by the antibody treatment. Since monovalent fragments of the antibodies also reduced the current but did not immobilize the cell, the electrophysiological effects were not the secondary consequences of immobilization. Antibodies against the 2nd most abundant family of proteins (42,000-45,000 MW) had similar electrophysiological effects as revealed by experiments in which the Paramecium and the serum were heterologous with respect to the i-antigen but homologous with respect to the 42,000-45,000-MW proteins. Protease treatment, shown to remove the surface antigen, also caused a reduction of the Ca-inward current. The loss of the inward Ca-current does not seem to be due to a drop in the driving force for Ca2+ entry since increasing the external Ca2+ or reducing the internal Ca2+ (through EGTA [ethylene glycol-bis(.beta.-aminoethyl ether) N,N,N'',N''-tetraacetic acid] injection) did not restore the current. The possibilities that the major proteins define the functional environment of the Ca-channel and that the Ca-channel is more susceptible to certain general changes in the membrane are discussed.