Received July 14, 2004
Revised August 24, 2004
Accepted after revision September 6, 2004

¹ Osaka Medical College
² Osaka Medical college

^* To whom correspondence should be addressed. E-mail: takan{at}art.osaka-med.ac.jp.

	Abstract

The ciliary beat frequency (CBF) of rat tracheal ciliary cells in a slice preparation was measured using video- enhanced contrast (VEC) microscopy. Acetylcholine (ACh) increased CBF mediated via intracellular Ca²⁺ concentration ([Ca²⁺]_i) in a dose- dependent manner. An adequate hypo-osmotic stress (-40 mosmol l^-1 (mosM)) potentiated ACh-stimulated CBF increase in tracheal ciliary cells and shifted the ACh-dose response curve to the low-concentration side. This potentiation was independent of hypo-osmotic stresses applied ranging from -20 mosM to -90 mosM. A hypo-osmotic stress induces ATP release in many cell types. The present study demonstrated that suramin (an inhibitor of purinergic receptor) and apyrase (the ATPase/ADPase ratio 1) eliminates the hypo- osmotic potentiation of ACh-stimulated CBF increase and that ATP increased[Ca²⁺]_i and CBF, and potentiated ACh-stimulated [Ca²⁺] _i and CBF increase. Moreover, the apical surface of tracheal ciliary cells are immunopositively stained for the P2X4 purinergic receptor. A hypo-osmotic stress (-40 mosM) transiently increased[Ca²⁺] _i and potentiated the ACh-stimulated [Ca²⁺]_i increase. The hypo-osmotic potentiation of ACh-stimulated CBF increase was not detected under a Ca²⁺-free condition. These observations suggest that a hypo-osmotic stress stimulates ATP release from the trachea. The released ATP induced further increases in [Ca²⁺] _i and CBF in ACh-stimulated tracheal ciliary cells mediated by purinergic receptors, such as P2X4.

Key Words: Adenosine 5'-triphosphate (ATP), Cilium, Purinoceptor