Angiotensin II excites paraventricular nucleus neurons that innervate the rostral ventrolateral medulla: an in vitro patch-clamp study in brain slices.
Neurons of the hypothalamic paraventricular nucleus (PVN) are key controllers of sympathetic nerve activity and receive input from angiotensin II (ANG II)-containing neurons in the forebrain. This study determined the effect of ANG II on PVN neurons that innervate in the rostral ventrolateral medulla (RVLM)-a brain stem site critical for maintaining sympathetic outflow and arterial pressure. Using an in vitro brain slice preparation, whole cell patch-clamp recordings were made from PVN neurons retrogradely labeled from the ipsilateral RVLM of rats. Of 71 neurons tested, 62 (87%) responded to ANG II. In current-clamp mode, bath-applied ANG II (2 muM) significantly (P < 0.05) depolarized membrane potential from -58.5 +/- 2.5 to -54.5 +/- 2.0 mV and increased the frequency of action potential discharge from 0.7 +/- 0.3 to 2.8 +/- 0.8 Hz (n = 4). Local application of ANG II by low-pressure ejection from a glass pipette (2 pmol, 0.4 nl, 5 s) also elicited rapid and reproducible excitation in 17 of 20 cells. In this group, membrane potential depolarization averaged 21.5 +/- 4.1 mV, and spike activity increased from 0.7 +/- 0.4 to 21.3 +/- 3.3 Hz. In voltage-clamp mode, 41 of 47 neurons responded to pressure-ejected ANG II with a dose-dependent inward current that averaged -54.7 +/- 3.9 pA at a maximally effective dose of 2.0 pmol. Blockade of ANG II AT1 receptors significantly reduced discharge (P < 0.001, n = 5), depolarization (P < 0.05, n = 3), and inward current (P < 0.01, n = 11) responses to locally applied ANG II. In six of six cells tested, membrane input conductance increased (P < 0.001) during local application of ANG II (2 pmol), suggesting influx of cations. The ANG II current reversed polarity at +2.2 +/- 2.2 mV (n = 9) and was blocked (P < 0.01) by bath perfusion with gadolinium (Gd(3+), 100 muM, n = 8), suggesting that ANG II activates membrane channels that are nonselectively permeable to cations. These findings indicate that ANG II excites PVN neurons that innervate the ipsilateral RVLM by a mechanism that depends on activation of AT1 receptors and gating of one or more classes of ion channels that result in a mixed cation current.
Cato
Matthew J
MJ
Dept. of Physiology-7756, Univ. of Texas Health Science Center, 7703 Floyd Curl Dr., San Antonio, TX 78229, USA.
Toney
Glenn M
GM
D000779:Anesthetics, Local / Q000494:pharmacology; D000804:Angiotensin II / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002104:Cadmium / Q000494:pharmacology; D003952:Diagnostic Imaging / Q000379:methods; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D017097:Electric Impedance; D018698:Glutamic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D008239:Lysine / Q000031:analogs & derivatives* / Q000378:metabolism; D008297:Male; D008526:Medulla Oblongata / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D009431:Neural Conduction / Q000187:drug effects; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D010286:Paraventricular Hypothalamic Nucleus / Q000166:cytology*; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D000779:Anesthetics, Local; D014662:Vasoconstrictor Agents; D002104:Cadmium; D000804:Angiotensin II; D018698:Glutamic Acid; D013779:Tetrodotoxin; C013411:biocytin; D008239:Lysine