Studies on reactivated cilia. II. Reactivation of ciliated cortices from the oviduct of Anolis cristatellus

Reactivation of newt lung cilia: evidence for a possible temperature- and MgATP-induced activation mechanism

Optimal conditions have been developed for the isolation and reactivation of highly coupled, demembranated ciliary axonemes from newt lungs [Hard, Cypher, and Schabtach, 1988, Cell Motil. Cytoskeleton 10:271-284]. In the present study, the motility of these cilia was further characterized by examining the effects of nucleotides, divalent cations, and temperature on beat frequency. When exposed to a reactivating solution containing Mg2+ and ATP, nearly 100% of the axonemes were motile and beat at frequencies of 0-50 Hz, depending on [MgATP] and temperature. Divalent cations were required for movement, with Mg2+ 2-3 times more effective than Ca2+. There was no absolute requirement for Ca2+ for motility. The beat frequencies obtained with fixed ATP and varying Mg2+ concentrations indicate that MgATP serves as the actual substrate. The effects of MgATP on beat frequency depended on the degree of mechanochemical coupling and temperature. When highly coupled preparations were reactivated at 21 degrees C, double reciprocal plots of beat frequency vs. [MgATP] were biphasic with extrapolated Fmax values of 22 and 44.8 Hz. However, when reactivated at 10 degrees C and 30 degrees C, linear plots were generated with Fmax values of 18.3 and 48.9 Hz, respectively. The beat frequencies of cultured cells and reactivated axonemes also varied biphasically with temperature. Our data suggest that newt lung respiratory cilia possess an intra-axonemal activation mechanism involving a temperature- and MgATP-induced transition between two distinct states whose maximum beat frequencies differ by 200-300%.

Isolation and reactivation of highly-coupled newt lung cilia

The paired lungs of the newt, Taricha granulosa, are simple, unbranched sacs, 3.5-5.0 cm in length. The inner epithelium overlying the pulmonary vein is differentiated into a mucociliary tract that extends the entire length of the lung. Populations of single, demembranated ciliary axonemes, 12-13 micron in length, can be isolated by extracting whole lungs or primary cultures of the ciliated epithelium with Triton X-100. The motile capabilities of the isolated axonemes are the highest yet obtained for any ciliary model. When exposed to a suitable reactivating medium containing Mg2+ and ATP, nearly 100% of the axonemes become motile. Uniform reactivation of high quality requires short extraction times, minimization of mechanical damage, and strict adherence to optimal conditions throughout the extraction, storage, and reactivation procedures. Significant deviations from either pH 7.0 or 0.12 M salt can lead to a rapid, irreversible decrease in the beat frequency of reactivated axonemes. Both DTT and EDTA serve to stabilize their motility. The isolated axonemes beat at 29.5 Hz in the presence of 1.75 mM ATP at 21 degrees C, matching the beat frequencies measured for cultured cells at the same temperature. With 5 mM ATP, beat frequencies over 40 Hz are measured. Our results show that neither the plasma membrane, accessory structures, nor hydrodynamic coupling of cilia are required for this activity and imply that the lack of these factors is not responsible for the low motile capabilities of ciliary models isolated previously.

Isolation of cilia from porcine tracheal epithelium and extraction of dynein arms

Milligram amounts of mammalian ciliary axonemes were isolated from porcine tracheas. These were reactivated upon addition of ATP, indicating intact functional capability with a mean beat frequency at 37 degrees C of 8.2 Hz. Electron microscopy showed typical ultrastructure of the isolated demembranated axonemes. Electrophoresis into polyacrylamide gradient gels containing sodium dodecyl sulfate revealed reproducible protein profiles from ten different tracheal preparations. Four major protein bands were observed in the 300-330 K molecular weight region, as well as tubulin at 51-54K. Extraction of the isolated tracheal axonemes with 0.6M KCl removed the outer dynein arms seen in electron microscopic cross-section of axonemes, preferentially solubilized two of the high molecular weight proteins at 320 and 330 K, and resulted in a three- to four-fold increase in ATPase specific activity. Sedimentation of the dialyzed salt extract on a 5-30% sucrose density gradient and subsequent fractionation yielded two peaks of ATPase activity. The faster migrating, 19S major ATPase peak correlated with the 320 and 330 K proteins, and two other proteins at 81 and 67 K. The slower sedimenting, 12S minor ATPase peak corresponded to a 308 K protein and two smaller proteins at 33 and 48 K. Thus, the outer dynein arm of tracheal cilia appeared to be associated with at least two high molecular weight proteins. These results demonstrate that adequate quantities of functionally intact axonemes can be reproducibly isolated from porcine tracheas, allowing further fractionation and analysis of mammalian cilia.

Newt lung ciliated cell models: effect of MgATP on beat frequency and waveforms

Highly coupled newt lung ciliated cell models were used to study the effects of MgATP concentration on ciliary beat frequency and waveform. Models were prepared from ciliated lung cells of the newt Taricha granulosa by trypsin dissociation of the epithelium, demembranation with Triton X-100, and reactivation with MgATP, as described previously [Weaver and Hard, 1985]. Beat frequencies were measured stroboscopically. Ciliary waveforms of reactivated models and intact mucociliary epithelial sheets were determined by single frame analysis of high-speed movies. Waveform parameters calculated included the durations of the effective and recovery strokes, the angular swings and angular velocities of the ciliary base and tip, the position of the bend along the ciliary shaft during the recovery stroke, the velocity of recovery stroke bend propagation, and the ratio of the duration of recovery stroke bend propagation to the duration of the recovery stroke itself. We found that beat frequency varied biphasically in response to MgATP at 21 degrees C, as shown previously for isolated, individual, newt lung axonemes. Apparent Fmax (maximum beat frequency) and Km values of 25 Hz and 0.14 mM, and 35 Hz and 0.47 mM, respectively, were obtained for each linear segment of the biphasic double reciprocal plot. Demembranation did not alter either ciliary waveform or the pattern of coordination. In this system, metachrony is antilaeoplectic and ciliary waveform appears to be regulated independent of beat frequency.

Isolation of newt lung ciliated cell models: characterization of motility and coordination thresholds

Demembranated ciliated cell models are useful for studying mechanisms responsible for the regulation of ciliary coordination and waveform. This paper describes procedures for isolating ciliated cells from the newt, Taricha granulosa, by trypsin dissociation, their subsequent demembranation by Triton X-100, and their reactivation with MgATP to produce highly motile, coordinated, ciliated cell models. Reactivation of cell models with a high degree of mechanochemical coupling depended on avoiding mechanical damage and maintaining optimal conditions during all stages of isolation and reactivation. Highly motile models were prepared from cells incubated in trypsin, treated briefly with EDTA, separated by gentle agitation, and concentrated by centrifugation at low gravitational forces. Optimal demembranation and reactivation conditions were similar to those described previously for isolated newt lung axonemes. Under these conditions, nearly 100% of the models were reactivated when provided with MgATP and 90-95% beat with coordinated waves. The ciliary tufts beat at frequencies within the range measured in living cells and their reactivated motility was stable for at least 30 min at constant MgATP. These highly coupled models were used to show (1) that development of coordination in the ciliary tuft occurs at a higher substrate concentration range (10-25 microM) than that required to initiate motility per se (2-10 microM; (2) that outer dynein arms may not contribute to beat frequency at substrate concentrations below 35 microM; and (3) that vanadate has effects both on beat frequency and coordination of the tufts.

Motile detergent-extracted cells of Tetrahymena and Chlamydomonas

Tetrahymena and Chlamydomonas cells treated with high (0.25-0.5%) concentrations of the detergent Nonidet P-40 in appropriate buffers retain the shape of the intact cells but are devoid of any ciliary activity unless supplied with MgATP. ATP causes them to swim actively, with beat parameters and swimming patterns indistinguishable from those of intact cells. Both types of detergent-extracted cells are completely devoid of ciliary membranes. The Tetrahymena preparations also lack all cellular membranes, whereas cellular membranes remain intact in the Chlamydomonas preparations. Experiments demonstrating the effects of ATP, ADP, vanadate, erythro-9-[3-2-(hydroxynonyl)]-adenine, and Ca++ are described to illustrate the use of these detergent-extracted cells in research on ciliary motility.

Immunocytochemical localization of tubulin, actin, and myosin in axonemes of ciliated cells from quail oviduct

Tubulin, actin, and myosin have been localized in isolated demembranated ciliated cells from quail oviduct by immunocytochemistry in both light and electron microscopy by using purified antibodies. The peripheral doublets and the central tubules are stained by the antitubulin whereas the kinetosomes are poorly stained. Actin antibodies clearly stain the axonemes, but only on the proximal-half portion, whereas myosin antibodies stain a small area of the axonemes just above the ciliary neck region.

Microtubule capping structures at the tips of tracheal cilia: evidence for their firm attachment during ciliary bend formation and the restriction of microtubule sliding

The distal tips of the central pair and A-microtubules are capped in mammalian and avian tracheal cilia. The capping structures are similar to those found in protozoan cilia and flagella [Dentler, 1981], and consist of a central microtubule cap that links the central microtubules to the membrane or to the ciliary crown and A-microtubule plugs that insert into the lumen of each of the A-microtubules. In contrast to the protozoan capping structures, each of the A-microtubule plugs is bound to the central microtubule cap by distal filaments. The ends of the central and outer doublet microtubules are tightly bound to the cap in both intact and in demembranated and reactivated tracheal cilia. Analysis of the displacement of the microtubule tips in cilia fixed at various bend angles revealed that the displacements of A-microtubules are only partially in agreement with those predicted by the sliding filament model [Satir, 1968]. These results are discussed with respect to the regulation of microtubule sliding in capped cilia and the role of the microtubule capping structures in microtubule assembly.

Microtubule sliding in cilia of the rabbit trachea and oviduct

Evidence for active sliding of microtubules during ciliary activity has been demonstrated in a number of organisms: sea urchin sperm flagella, protozoan cilia, and mollusc gill cilia. Although there is evidence that active sliding also occurs in mammalian sperm flagella, there is little or no information on whether active sliding of microtubules also occurs in the short (5-micron) cilia of the mammalian trachea or oviduct. Since these cilia are important in tracheobronchial clearance and ovum transport, respectively, it has been important to demonstrate that microtubule sliding is also involved in the activity of somatic cilia. Ciliated apical portions (cortices) and cilia were isolated from rabbit trachea and oviduct, using Triton X-100 to demembranate the cilia. Most of the ciliated cortices reactivated upon addition of ATP, whereas isolated cilia reactivated to a lesser extent. When preparations of cilia were digested with trypsin before or after ATP addition, disintegration of axonemal doublets occurred with about the same frequency as reactivation. These events were recorded using Nomarski optics and dark-field microscopy. When isolated cilia which had been digested by trypsin and exposed to ATP were also prepared for electron microscopy by negative staining, telescoping of doublet microtubules from axonemes could be shown. These results demonstrate that mammalian somatic ciliary doublet microtubules actively slide in a manner similar to that described for invertebrate cilia.