The presence of ATP and adenosine receptors and their role in controlling ciliary activity in oviductal ciliated cells was studied by measuring the ciliary beat frequency (CBF) in oviductal tissue cultures. ATP, adenosine, and related compounds increased the CBF in a dose-dependent manner. We established that P2 receptors of subtype 2Y2 and P1 receptors of subtype A2a mediated the responses to ATP and adenosine, respectively. We found evidence to suggest that stimulation of ciliary activity by ATP requires d- myo-inositol 1,4,5-trisphosphate [Ins(1,4,5) P 3] metabolism, intracellular Ca2+ mobilization, and protein kinase C activation. On the other hand, the adenosine effect is mediated by activation of a Gs protein-dependent pathway that enhances cAMP intracellular levels. To study the interaction between P2 and P1 receptors, cells were stimulated simultaneously with both agonists. We observed a synergistic increase of the CBF even at agonist concentrations (100 nM) that did not produce a significant response when added separately to the culture. Furthermore, a blocker of the cAMP pathway produced a reduction of the ATP response, whereas a blocker of the Ins(1,4,5) P 3 pathway also produced an inhibition of the adenosine response. Our evidence demonstrates that both ATP and adenosine receptors are present in a single ciliated cell and that a mechanism of cross talk could operate in the transduction pathways to control ciliary activity.
Adenosine Induced Apoptosis in BHK Cells via P1 Receptors and Equilibrative Nucleoside Transporters
