We compared the electrophysiological properties of neurons in the rostral ventrolateral medulla (RVLM) of neonatal Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR), and responses to angiotensin II and its type 1 receptor antagonist candesartan. Using the whole-cell patch-clamp technique, we examined the characteristics of RVLM neurons in brainstem-spinal cord preparations with a preserved sympathetic neuronal network. The baseline membrane potential of irregularly firing

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... was less negative (Ϫ50.1Ϯ0.6 versus Ϫ52.0Ϯ0.6 mV) and the firing rate was faster (3.0Ϯ0.2 versus 2.0Ϯ0.2 Hz) in SHR (nϭ56) than in WKY (nϭ38). Superfusion with angiotensin II (6 mol/L) significantly depolarized the RVLM bulbospinal neurons in SHR (5.4Ϯ1.1 mV, nϭ15) but not in WKY. In contrast, candesartan (0.12 mol/L) induced a significant membrane hyperpolarization (Ϫ3.7Ϯ0.4 mV; nϭ14) and a decrease in the firing rate in RVLM bulbospinal neurons of SHR but not of WKY. These results suggest that endogenously generated angiotensin II binds to type 1 receptors on RVLM bulbospinal neurons, thus tonically contributing to a higher membrane potential and a faster firing rate in SHR. The electrophysiological properties of RVLM neurons and their responses to angiotensin II and candesartan differ between neonatal WKY and SHR. These differences in RVLM neurons suggest a mechanism that possibly leads to elevation in blood pressure. (Hypertension. 2002;40:560-565.)