title: Membrane potential measurements in renal afferent and efferent arterioles: actions of angiotensin II.
abstract: An adaptation of the in vitro perfused hydronephrotic rat kidney model allowing in situ measurement of arteriolar membrane potentials is described. At a renal perfusion pressure of 80 mmHg, resting membrane potentials of interlobular arteries (22 +/- 2 microns) and afferent (14 +/- 1 microns) and efferent arterioles (12 +/- 1 microns) were -40 +/- 2 (n = 8), -40 +/- 1 (n = 45), and -38 +/- 2 mV (n = 22), respectively (P = 0.75). Using a dual-pipette system to stabilize the impalement site, we measured afferent and efferent arteriolar membrane potentials during angiotensin II (ANG II)-induced vasoconstriction. ANG II (0.1 nM) reduced afferent arteriolar diameters from 13 +/- 1 to 8 +/- 1 microns (n = 8, P = 0.005) and membrane potentials from -40 +/- 2 to -29 +/- mV (P = 0.012). ANG II elicited a similar vasoconstriction in efferent arterioles, decreasing diameters from 13 +/- 1 to 8 +/- 1 microns (n = 8, P = 0.004), but failed to elicit a significant depolarization (-39 +/- 2 for control; -36 +/- 3 mV for ANG II; P = 0.27). Our findings thus indicate that resting membrane potentials of pre- and postglomerular arterioles are similar and lie near the threshold activation potential for L-type Ca channels. ANG II-induced vasoconstriction appears to be closely coupled to membrane depolarization in the afferent arteriole, whereas mechanical and electrical responses appear to be dissociated in the efferent arteriole.
authors.affiliation: University of Calgary, Department of Pharmacology and Therapeutics, Alberta, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Loutzenhiser
authors.forename: L
authors.initials: L
authors.lastname: Chilton
authors.forename: G
authors.initials: G
authors.lastname: Trottier
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000502:physiology; D006869:Hydronephrosis / Q000503:physiopathology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012079:Renal Circulation / Q000187:drug effects*; D014661:Vasoconstriction; D014662:Vasoconstrictor Agents / Q000494:pharmacology
chemical_list: D014662:Vasoconstrictor Agents; D000804:Angiotensin II