Calcium sensitivity extends the length of ATP-reactivated ciliary axonemes.

Abstract

We use the Ca-dependent activation response of macrocilia of the ctenophore Beroe to map the distribution of Ca sensitivity along axonemes of detergent-extracted ATPreactivated models. Local iontophoretic application of Ca (or Sr or Ba) to any site along the length of demembranated macrocilia in ATP-Mg solution elicits oscillatory bending. Bending responses are localized to the site of application of these cations and do not propagate. Ca sensitivity for initiating bends is, therefore, distributed along the entire length of the axonemes. Since Ca triggers ATP-dependent microtubule sliding disintegration of macrociliary axonemes, a Ca-sensitive mechanism for activating microtubule sliding extends the length of the axonemes. In contrast, local application of Ca to living dissociated macrociliary cells elicits beating only when applied to the base of the macrocilium, indicating that the effective site of Ca entry is localized to the membrane at the ciliary base. Therefore, the spatial distributions of membrane Ca permeability and axonemal Ca sensors do not coincide.Calcium ions (Ca) play a key role in signaling various modifications of ciliary and flagellar motility in response to environmental stimuli. Ca-triggered behavioral responses include: reorientation of ciliary beat direction (1-3), reversal of flagellar wave direction (4), alteration of flagellar waveform (5-8), arrest of beating (9-11), and activation of beating (12,13).Stimulus-evoked increase in intraciliary Ca concentration is mediated by voltage-gated Ca channels in the ciliary membrane (14-16). Electrophysiological recording from ctenophore comb plate cilia showed that the Ca conductance controlling reversal of beat direction is distributed over most of the length of the ciliary membrane (17).Macrocilia of the ctenophore Beroe are compound organelles containing hundreds (or thousands, depending on species) of "9+2" ciliary axonemes enclosed by a single common membrane (18), except at the base (19). Macrocilia are usually quiescent but are activated to beat rapidly and continuously by depolarization-gated Ca influx (13). Extracellular application of Ca to various sites along macrocilia of heat-dissociated cells indicated that Ca permeability for triggering beating is localized to the basal region of the macrociliary membrane, corresponding to a rete of unfused ciliary membranes (19).Little is known about the site(s) and mechanism(s) ofaction of Ca within the axoneme. Detergent-permeabilized models of macrocilia that require micromolar levels of free Ca, Ba, or Sr for ATP reactivation of beating and/or microtubule sliding disintegration have been devised (20). In this report we iontophoretically apply these cations at various regions along demembranated macrocilia in ATP to map the distri- (Fig. 1). MATERIALS AND METHODSPermeabilized Models. Lip pieces bearing macrocilia were washed in Ca-free artificial seawater for 30 min. Tissue was then extracted in 0.05% or 0.1% saponin (B. ovata) or 0.05%

Photolysis of caged calcium in cilia induces ciliary reversal inParamecium caudatum

“…This result coincides well with observations that local iontophoretic application of Ca 2+ to any site along the length of demembranated macrocilia of B. mitrata elicits oscillatory bending, indicating that Ca 2+ sensitivity extends the length of the cilia (Tamm and Tamm, 1989), that Ca 2+ inward current decreases upon removal of cilia and recovers accompanying ciliary regrowth, indicating that voltage-sensitive Ca 2+ channels are present throughout the cilia of P. caudatum (Machemer and Ogura, 1979), and that fluorescence of Calcium Green rises at a similar rate along the ciliary length during ciliary reversal in Mnemiopsis leidyi (Tamm and Terasaki, 1994). Our findings are not necessarily consistent, however, with the fact that iontophoretic application of Ca 2+ to the ciliary base of a permeabilized P. caudatum cell induces ciliary reversal, though the application to the ciliary tip does not (Hamasaki and Naitoh, 1985).…”

“…Their study revealed that the basal region of the permeabilized cilium is the most sensitive to Ca 2+ in inducing ciliary reversal. In contrast, Tamm and Tamm (1989) showed that the Ca 2+ sensitivity extended the length of cilia, using detergentpermeabilized macrocilia of Beroë mitrata. In an effort to more faithfully represent the natural conditions of cilia, however, we used living Paramecia, rather than a detergent-permeabilized system in the present study, to prevent any possible loss of Ca 2+ sensitivity through the permeabilization procedure.…”

Visualization of calcium transients controlling orientation of ciliary beat.

“…Local iontophoretic application of Ca at different sites along Ca-permeable macrocilia of heat-dissociated cells showed that Ca does not enter along the entire ciliary shaft (as in comb plates), but only at the base of the macrocilium where the membranous rete is located (Tamm, 1988b). Similar Ca iontophoresis experiments on demembranated ATP-reactivated macrocilia showed, surprisingly, that Ca-sensitivity for activating bending is not restricted to the base of the axonemes but occurs along their entire length (Tamm and Tamm, 1989). Does Ca normally enter macrocilia only at the base, and act there to trigger beating?…”

Breakup and then makeup: a predictive model of how cilia self-regulate hardness for posture control

“…In the context of messaging mechanisms740, ATP oscillators couple with the Ca 2+ -oscillator to regulate the CBL architecture, which alters the beat frequency. The precision of hardness can be controlled one CBL link at a time—a precision beyond the reach of current engineering.…”