Reactivation of outer‐arm‐depleted lung axonemes: Evidence for functional differences between inner and outer dynein arms in situ

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Abstract
Demembranated axonemes isolated from newt lung ciliated cells show a complex beat frequency response to varying [MgATP] and temperature [Hard and Cypher, 1992, Cell Motil. Cytoskeleton 21:187–198]. The present study was undertaken to ascertain whether the beat frequency of outer‐arm‐depleted newt lung axonemes is controlled in a manner similar to that of intact axonemes. Populations of demembranated ciliary axonemes were isolated by Triton X‐100 extraction of lungs from the newt, Taricha granulosa. Aliquots of the demembranated axonemes were further treated with solutions containing high salt (0.375 M KCl) and 1.25 mM MgATP. This treatment resulted in the selective removal of outer dynein arms and a concomitant decrease in beat frequency to a stable level, 33–35% of control values. The effects of pH, salt concentration, nucleotides, and temperature on the beat frequency of reactivated outer‐arm‐depleted axonemes were ascertained and compared with those of intact axonemes. Some reactivation properties, such as nucleotide specificity, the effect of pH on beat frequency and the threshold [MgATP] required for reactivation (approximately 5 μM) were similar to those observed for intact axonemes. Other properties, such as the relationship between beat frequency and varying [MgATP] or salt concentration, differed both qualitatively and quantitatively from those of control axonemes, as did their response to temperature over the range, 5°–32°C. The nature of the results obtained with temperature and MgATP suggests that inner and outer dynein arms are not functionally equivalent in situ.