Aim: The aim of the present work is to study underlying mechanisms for ventricular cilia movement that drives the flow of cerebrospinal fluid.
Methods: Brain slices, 150 μm thickness and including the third ventricle, were obtained from adult mice. The beat frequency, an index of ciliary activity, was measured using an inverted microscope and a high-speed digital camera at 210 frames per second (CASIO; EXLIM EX-FC100).
Results: The beating frequency of ependymal cilia was 24.3 ± 4.5 Hz (n = 25) in standard solution at 36°C. T-type Ca²⁺ channels and hyperpolarization-activated I_h channels, known to contribute to the rhythmic contraction of the heart, are not involved in ciliary movement since the movement did not show any change in the presence of their specific blockers, NNC 55-0396 or ivabradine. Contribution of other types of voltage-dependent Ca²⁺ channels (L-type etc.) was also found to be negligible. In contrast, the beating of cilia was drastically suppressed when external Na⁺ was omitted, but it was not affected by a Na⁺ channel blocker, tetrodotoxin. In contrast, beating was facilitated when external Ca²⁺ was removed from perfusate. Furthermore, the activity of cilia was suppressed by a blocker of the epithelial Na⁺ channel (amiloride), while it was facilitated by an inhibitor of the Na⁺/Ca²⁺ exchanger (benzamil) or by a blocker of the Na⁺/K⁺/Cl^- cotransporter (bumetanide). Trichlormethiazide, a Na⁺/Cl^- cotransporter suppressor, was not effective. Although ciliary activity completely recovered from all of the above-mentioned suppression or facilitation, it only showed a partial recovery when cilia were exposed to CCCP, an uncoupler of oxidative phosphorylation in mitochondria.
Conclusion: The motility of ependymal cell cilia in the third ventricle of the mouse brain is not regulated by voltage-dependent ion channels such as Na⁺, Ca²⁺, or I_h channels, but is dependent on external Na⁺, and is controlled mainly by epithelial Na⁺ channels and Na⁺ transporters.