The interaction of the benzothiazolamine R 56865 with the nifedipine-sensitive component of the serotonin (5-HT)-, angiotensin II (AII)- and arginine-vasopressin (AVP)-induced contractions was studied in the isolated rat aorta. Nifedipine caused concentration-dependently (10–9–10–6 mol/l) a slight rightward shift accompanied by a limited depression of the maximum of the concentration-response curves for 5-HT-, All- and AVP-induced contractions. R 56865 (10–5 mol/l) antagonized the contraction elicited by 5-HT and AII in a similar manner as nifedipine. The effect of R 56865 on 5-HT- and All-induced contractions was no longer observed after pretreatment with nifedipine. The AVP-induced contraction was not affected by R 56865 (10–5 mol/l). As shown previously [3], R 56865 is a weak inhibitor of potential-operated channels but inactive on Ca2+ channels activated by NA. In conclusion, R 56865 does not only differentiate between depolarization and receptor-stimulation, but also between the activation of Ca2+ channels by different types of receptors. We propose that R 56865 may interact with Ca2+ channels at a site which plays a role in their activation.

Keywords:
Rat aorta, R 56865, Nifedipine, Contraction, Calcium
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© 1989 S. Karger AG, Basel
1989
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