Effects of benzocaine on vascular smooth muscle contractility of the sea lamprey dorsal aorta

Abstract

Benzocaine is a common fish anesthetic. This experiment was undertaken in order to determine the action of benzocaine and the mechanisms of action of calcium in the vascular smooth muscle from the dorsal aorta (LDA) of sea lamprey (Petromyzon marinus). Benzocaine contracted otherwise unstimulated vessels and vessels precontracted with either norepinephrine (NE) or KCl in a dose dependent manner. The vehicle, ethanol, also effected contraction in a dose dependent manner. LDA contracted significantly more when exposed to benzocaine in ethanol than to an equal volume of ethanol alone. LDA stimulated with NE were significantly more sensitive to benzocaine than were either unstimulated LDA or in LDA precontracted with KCl. LDA stimulated with KCl contracted significantly less in the absence of extracellular (EC) Ca2+ but the contractions doubled when EC Ca2+ was added back. Ethanol contractions were insignificant in the absence of EC Ca2+. Benzocaine‐induced contractions of LDA treated with thapsigargin and caffeine were significantly reduced in both the presence and absence of EC Ca2+. Therefore, KCl− and ethanol‐induced contractions were found to be dependent upon EC Ca2+ entry, while benzocaine was dependent upon intracellular Ca2+, most likely from the sarcoplasmic reticulum. These are important considerations to take into account when anesthetizing fish, particularly cyclostomes.