Protein kinase C induced calcium influx and sustained enhancement of ciliary beating by extracellular ATP

The major purpose of this work was to determine protein kinase C (PKC) influence on ciliary beat frequency (CBF) and to assess participation of PKC in purinergic ciliary stimulation. The experiments were performed by simultaneous measurement of [Ca²⁺](i) and CBF on tissue culture of frog esophagus epithelium. The PKC activators TPA and DiC₈ produced significant elevation of [Ca²⁺](i) and strong frequency enhancement. The calcium elevation was inhibited by lowering the extracellular calcium level, or by La³⁺, but was unaffected by verapamil and the phospholipase C inhibitor U-73122, suggesting that Ca²⁺ influx was via non-voltage-operated calcium channels. The inhibition of [Ca²⁺](i) elevation resulted in corresponding inhibition of CBF enhancement. The effect of TPA was blocked by the selective PKC inhibitors chelerythrine, calphostin C, and GF109203X, and by the enzyme downregulation. The downregulation of PKC, or the enzyme inhibitors did not affect the immediate response to extracellular ATP but caused rapid decay of initially stimulated [Ca²⁺](i) and CBF to the basal level. These results suggest that PKC produces CBF enhancement via activation of calcium influx through non-voltage-operated calcium channels. This calcium influx seems to be responsible for the duration of ciliary stimulation produced by the extracellular ATP.