Effects of prostanoids on isolated feline cerebral arteries. II. Roles of extra- and intracellular calcium for the prostaglandin F2 alpha-induced contraction.
The roles of extra- and intracellular calcium for the contractile effects of PGF2 alpha in the feline basilar artery (BA) were investigated. Comparisons were made with contractions induced by K+ and noradrenaline (NA). Addition of nifedipine to PGF2 alpha- or K+ (124 mM)-contracted arteries resulted in an incomplete relaxation, whereas NA-contracted vessels were completely relaxed. Incubation of the preparations in a calcium-free medium containing 10(-5) M EGTA for 5-10 min almost abolished contractions induced by K+ and NA. In contrast, 63% of the response to PGF2 alpha remained after pretreatment of the arteries in a calcium-free solution for 40 min; PGF2 alpha produced a biphasic contraction in 17 out of 20 preparations consisting of a rapidly developing initial phase followed by a second increase in tension after 1-6 min. The second phase was absent if the EGTA-concentration was increased to 10(-4) M, or if the arteries were pre-treated with nifedipine. After incubation of the arteries in a calcium-free medium for 40-120 min and K+-depolarization, re-addition of calcium elicited contractions at lower concentrations in the presence of PGF2 alpha than in controls. The results suggest that PGF2 alpha-induced contractions in the feline BA are considerably less dependent on extracellular calcium than contractions evoked by K+ or NA. PGF2 alpha appears to be able to release calcium from two cellular stores, and may also promote calcium influx through the cell membrane.
D000818:Animals; D001488:Basilar Artery / Q000187:drug effects*; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002415:Cats; D002463:Cell Membrane Permeability / Q000187:drug effects; D003470:Culture Media; D015237:Dinoprost; D007473:Ion Channels / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011460:Prostaglandins F / Q000494:pharmacology*
D003470:Culture Media; D007473:Ion Channels; D011460:Prostaglandins F; D015237:Dinoprost; D009543:Nifedipine; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine