OPTICAL ANALYSIS OF THE FLAGELLAR RIBBON BEAT CYCLE IN THE FISH NEPHRON

Flagella rarely occur on somatic cells in the Vertebrata. When present , they exist only as single projections of the cell surface. Recent st udies have revealed specialized cells in fish nephrons, each of which has multiple flagella aligned in parallel rows and tightly packed into a single ribbon. In the present study the dynamics of these ribbons w as studied by stroboscopic microscopy of isolated perfused renal tubul e segments of elasmobranch and teleost fish. All ribbons beat in the s ame direction, away from the glomerulus, and function to force fluid a long the tubule. The flagellar ribbons beat with effective and recover y strokes comparable to those of a cilium but differ in the extent of the excursion which in each stroke covers an angle of less than 90 deg rees. Furthermore, during the recovery stroke the ribbon gradually ret racts to its original position by arching upwards towards the tubule l umen. It neither bends deeply, close to the epithelial surface, nor mo ves laterally, as usually do some cilia. Each flagellar ribbon may spo ntaneously change its beat period (length of the beat cycle) and its b eat frequency (beat cycle/sec); moreover, both period and frequency ma y be different between different ribbons in the same tubule and may be affected by alterations of the perfusion pressure. Some ribbons show a resting phase of varying periods. Trajectories of latex particles ad ded to the tubular perfusate vary from straight to irregular and there fore the transport speed is also extremely variable. The direction of the beat of the flagellar ribbons is determined by their subcellular o rganization because they all continue to beat in the same direction wh en perfusion now is stopped and when the flow is reversed the ribbon b eat is disrupted, erratic, and irregular.