Characterization of membrane potentials in vascular smooth muscle of hagfish, lamprey and trout

The objective of this study was to characterize membrane potentials in systemic arteries of Pacific hagfish, Eptatretus stouti, Rainbow trout, Onchorhyncus mykiss, and Sea lamprey Petromyzon marinus. Previous studies have characterized membrane potentials in piscine tissue. However, these studies utilized non-vascular tissues such as cardiac muscle and skeletal muscle (69, 161). Characterization of membrane potentials in fish vasculature is without precedent in the literature. The hypothesis of this study was that membrane potentials in fish vascular smooth muscle differ little between species when comparable vasculature is evaluated.; Histological evaluations were conducted to assess the suitability of fish arteries for electrophysiology studies. Arteries were histologically prepared and examined using microscopy (n=35 slides). These examinations revealed vascular components (e.g., endothelial cells, connective tissue, and smooth muscle cells) similar to that reported in other animals (21, 27, 32, 62, 71, 92, 110, 131, 134, 159, 160). Osmometry and spectrophotometric techniques were used to prepare species specific physiological saline solutions for use in histology and electrophysiology experiments.; Resting membrane potential and the response to changes in extracellular potassium was evaluated in hagfish and lamprey dorsal aortas and trout efferent branchial arteries. Membrane potentials were measured using sharp microelectrodes to impale continuously perfused arteries. Membrane potential in unstimulated systemic arteries were similar: -52.7 +/-2.9 mV, n=15 (hagfish), -54.3 +/-5.2 mV, n=32 (lamprey) and -48.3 +/-1.6 mV, n=27 (trout) (p >0.05, ANOVA). Increasing the perfusate KCl concentration to 100 mM depolarized hagfish vascular smooth muscle cells 42.6 +/-6.6 mV, n=5 and 80 mM KC1 depolarized lamprey vascular smooth muscle cells 40 +/-2 mV, n=7. Switching the KCI concentration back to normal repolarized potassium depolarized cells.; Unexpectedly, the anesthetic used in this study (benzocaine) altered vascular tone. The effects of benzocaine on vascular tone were subsequently evaluated using a gas chromatography/mass spectrometry method developed for this study and via myography. Benzocaine induced contraction in lamprey aortas and relaxation in trout arteries.; The present study suggests that membrane potentials are similar in comparable fish vasculature despite differences in vascular morphology and differences in the composition of intracellular and extracellular constituents. Additionally, this study suggests benzocaine possesses vasoactive properties in fish systemic arteries at anesthetic concentrations.