Possible calcium channel modulating activity of iloprost in rabbit isolated vascular segments

1. Iloprost produced a concentration-dependent decrease in the contractile responses to K+ and NA in CoeA and SMA strips without altering the responses in RA, MPA, CaA and ThA. 2. Nifedipine and verapamil also inhibited the contractile responses to NA and K+ in CoeA and SMA rings in a concentration dependent manner. 3. Removal of endothelium did not alter the inhibitory effects of iloprost and Ca2+ channel blockers in the investigated arterial segments. 4. In Ca2+ free and high K+ medium both iloprost and Ca2+ channel blockers potentially inhibited the contractile effect of external Ca2+. 5. Iloprost at lowest concentration which is not influence the contractile response of K+ can potentiate the inhibitory effect of nifedipine in CoeA and SMA rings without altering its inhibitory effect on NA responses. 6. These results suggest that iloprost may modulate Ca2+ entry into the cell probably by acting through the potential-operated Ca2+ channels in CoeA and SMA. These results also indicate that Ca2+ channels are heterogenously functioned in various vascular segments of rabbit.