Gadolinium and mechanotransduction of rat aortic baroreceptors.
The cellular mechanisms enabling baroreceptors to transduce wall distortion into axonal discharge are unknown but might involve stretch-activated ion channels. Gadolinium (Gd3+, 10 microM) blocks stretch-activated channels in several preparations. Here we tested Gd3+ effects on discharge responses of 15 single-fiber baroreceptors in vitro. We simultaneously measured discharge, pressure, and aortic diameter at Gd3+ concentrations from 0.001 to 400 microM. High levels of Gd3+ added to a bicarbonate-buffered perfusate (Krebs) slightly shifted the pressure-discharge relation (less than 4 mmHg, n = 3, P = 0.01) without affecting slope or discharge frequency at threshold. Gd3+ in Krebs variably altered the pressure-diameter relation. Because 500 microM Gd3+ produced visible precipitate in Krebs, we tested Gd3+ in a simpler perfusate using N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES). Gd3+ in HEPES (n = 10) induced minor, but statistically significant, average increases in threshold (less than +5-7%) and no changes in gain. However, prolonged HEPES exposure alone (n = 2) produced similar shifts. Electron microscopy verified that Gd3+ diffused from the lumen to reach extracellular locations near baroreceptor endings. We conclude that 1) HEPES perfusate alone reversibly depresses baroreceptor discharge and 2) Gd3+ has no direct effects on baroreceptors. Thus it appears that aortic baroreceptor mechanotransduction must utilize a different class of stretch-activated ion channels.
Andresen
M C
MC
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.
Yang
M
M
D000818:Animals; D001011:Aorta / Q000294:innervation*; D004056:Differential Threshold; D005682:Gadolinium / Q000494:pharmacology*; D006531:HEPES / Q000494:pharmacology; D007552:Isotonic Solutions / Q000494:pharmacology; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology*; D009994:Osmolar Concentration; D010477:Perfusion; D011311:Pressoreceptors / Q000187:drug effects / Q000502:physiology*; D011312:Pressure; D051381:Rats; D011919:Rats, Inbred Strains; D015398:Signal Transduction / Q000187:drug effects*
D007552:Isotonic Solutions; C051865:Krebs-Ringer solution; D005682:Gadolinium; D006531:HEPES