Spontaneous contractions in elasmobranch vessels in vitro

Isolated vessels from four elasmobranchs, yellow stingray (Urolophus jamaic ensis), clearnose skate (Raja eglanteria), ghost shark (Hydrolagus novaezel andiae), and spiny dogfish (Squalus acanthias), were examined for the prese nce of spontaneous contractions (SC). SC were observed in otherwise unstimu lated dorsal aortas (DA) from stingray and ghost shark, but not in skate DA . Unstimulated ventral aortas (VA) did not exhibit SC. After treatment of V A with a contractile agonist, SC appeared in stingray and skate but not gho st shark or dogfish. SC in stingray VA were subsequently inhibited by eithe r epinephrine (10(-5) M) or indomethacin (10(-4) M). Agonist contraction al so elicited strong SC in ductus Cuvier from stingray, but not from ghost sh ark or dogfish. SC in dogfish hepatic portal veins (HPV) produced a rhythmi cal oscillation in tension. The frequency of HPV SC was highest (similar to 1 min(-1)) in intact veins and lower (similar to 3 min(-1)) in vein segmen ts, indicative of a dominant pacemaker in the intact vessel. SC in HPV were depressed during the first 30 min of hypoxia, but there was substantial re covery over an additional 30 min of hypoxia and complete recovery upon retu rn to normoxia. Addition of 80 mM KCl completely inhibited HPV SC and lower ed resting tone. These results show that SC are a common feature of elasmob ranch vessels and there appears to be a correlation between swimming behavi or and the propensity for SC. KCl inhibition of SC and tonus in HPV is high ly unusual for vascular smooth muscle. J. Exp. Zool. 286:606-614, 2000. (C) 2000 Wiley-Liss, Inc.