Fig. 7. Effect of cytochalasin D (CD; 0.5 µg ml^–1) pretreatment on a sternal artery (SA) ring and an ostial muscle (OOM). (A) Contraction of an SA ring in response to continuous perfusion with proctolin (PR; 1.0 µmol l^–1). (B) Effect of CD pretreatment on a PR-induced contraction in an adjacent SA ring. (C) Effect of CD (2.5 min) on basal tonus and electrically stimulated tetanic contractions of an OOM.