Fig. 1. Intracellular Ca²⁺ ([Ca²⁺]_i) responses of shark VSM to ET_BR receptor agonists and endothelin-1 (ET-1). (A) The ET_BR agonists IRL 1620 and sarafotoxin S6c (SRX) produce the same increase in [Ca²⁺]_i as ET-1. (B) Representative tracing of the cytosolic calcium responses of shark anterior mesenteric artery VSM. The ET_BR agonist IRL 1620 causes a prompt increase in [Ca²⁺]_i. In the continued presence of IRL 1620, addition of ET-1 does not cause any further significant peak increase in [Ca²⁺]_i.