Role of extracellular and intracellular sources of Ca2+ in sarafotoxin S6b-induced contraction of strips of the rat aorta.
1. The effect of sarafotoxin S6b (sarafotoxin), a vasoconstrictor peptide, on cytosolic Ca2+ concentration ([Ca2+]i) and force in rat aortic strips loaded with fura-2 was determined by front-surface fluorometry. The objective was to elucidate the role of extracellular and intracellular Ca2+ in the mechanism of action of this peptide. 2. In the presence of extracellular 1.25 mM Ca2+, sarafotoxin induced a biphasic response consisting of an initial rapid increase in [Ca2+]i followed by a secondary sustained increase. Tension developed slowly but was sustained during the application of sarafotoxin. Diltiazem (10 nM-0.1 mM) partially inhibited both the increases in [Ca2+]i and tension. 3. In the presence of extracellular Ca2+, the force developed in relation to the increase in [Ca2+]i ([Ca2+]i-force relationship) observed with sarafotoxin was much greater than that observed upon K+ depolarization. In the presence of diltiazem the sarafotoxin-induced [Ca2+]i-force relationship was shifted even further to the left. 4. In the absence of extracellular Ca2+, sarafotoxin induced a transient increase in [Ca2+]i and a sustained contraction. Extending the incubation time in Ca(2+)-free physiological solution, resulted in smaller responses. However, after 60 min in Ca(2+)-free solution, sarafotoxin induced a sustained contraction but no change in [Ca2+]i. This residual contraction was inhibited by H-7, which is known to inhibit protein kinase C. 5. After treatment with caffeine to reduce intracellular stored Ca2+, sarafotoxin could still elicit increases in [Ca2+]i and in tension, showing that the caffeine-sensitive intracellular Ca2+ store partially overlaps with the sarafotoxin-sensitive store. 6. We conclude that, in addition to those components of contraction dependent on extracellular- and on intracellularly stored Ca2 , sarafotoxin can also induce contraction without increasing [Ca2+],. This component may be partially linked to the activation of protein kinase C and may contribute, in part, to the leftward shift of the [Ca2+]i-force relationship in the presence of sarafotoxin.
Watanabe
C
C
Division of Molecular Cardiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Hirano
K
K
Kanaide
H
H
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004110:Diltiazem / Q000494:pharmacology; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010879:Piperazines / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D013050:Spectrometry, Fluorescence; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014757:Viper Venoms / Q000494:pharmacology*
D007546:Isoquinolines; D010879:Piperazines; D014662:Vasoconstrictor Agents; D014757:Viper Venoms; C057354:sarafotoxins s6; D002110:Caffeine; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011493:Protein Kinase C; D004110:Diltiazem; D002118:Calcium