Role of small conductance calcium-activated potassium channels expressed in PVN in regulating sympathetic nerve activity and arterial blood pressure in rats

Abstract

Role of small conductance calcium-activated potassium channels expressed in PVN in regulating sympathetic nerve activity and arterial blood pressure in rats. Am J Physiol Regul Integr Comp Physiol 303: R301-R310, 2012. First published May 30, 2012 doi:10.1152/ajpregu.00114.2012.-Small conductance Ca 2ϩ -activated K ϩ (SK) channels regulate membrane properties of rostral ventrolateral medulla (RVLM) projecting hypothalamic paraventricular nucleus (PVN) neurons and inhibition of SK channels increases in vitro excitability. Here, we determined in vivo the role of PVN SK channels in regulating sympathetic nerve activity (SNA) and mean arterial pressure (MAP). In anesthetized rats, bilateral PVN microinjection of SK channel blocker with peptide apamin (0, 0.125, 1.25, 3.75, 12.5, and 25 pmol) increased splanchnic SNA (SSNA), renal SNA (RSNA), MAP, and heart rate (HR) in a dose-dependent manner. Maximum increases in SSNA, RSNA, MAP, and HR elicited by apamin (12.5 pmol, n ϭ 7) were 330 Ϯ 40% (P Ͻ 0.01), 271 Ϯ 40% (P Ͻ 0.01), 29 Ϯ 4 mmHg (P Ͻ 0.01), and 34 Ϯ 9 beats/min (P Ͻ 0.01), respectively. PVN injection of the nonpeptide SK channel blocker UCL1684 (250 pmol, n ϭ 7) significantly increased SSNA (P Ͻ 0.05), RSNA (P Ͻ 0.05), MAP (P Ͻ 0.05), and HR (P Ͻ 0.05). Neither apamin injected outside the PVN (12.5 pmol, n ϭ 6) nor peripheral administration of the same dose of apamin (12.5 pmol, n ϭ 5) evoked any significant changes in the recorded variables. PVNinjected SK channel enhancer 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one (DCEBIO, 5 nmol, n ϭ 4) or N-cyclohexyl-N-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-4-pyrimidin]amine (CyPPA, 5 nmol, n ϭ 6) did not significantly alter the SSNA, RSNA, MAP, and HR. Western blot and RT-PCR analysis of punched PVN tissue showed abundant expression of SK1-3 channels. We conclude that SK channels expressed in the PVN play an important role in the regulation of sympathetic outflow and cardiovascular function. paraventricular nucleus; heart rate; sympathetic nervous system; cardiovascular function ACTIVITY of presympathetic hypothalamic paraventricular nucleus (PVN) neurons regulate the sympathetic nervous system (11,12,47,51) response to physiological challenges. These neurons also play a well-described role in activating the sympathetic nervous system in cardiovascular diseases (17,28,36,39,47,48,51,53). Even with the significant literature support for the role of presympathetic PVN neurons in controlling sympathetic nerve activity (SNA) and arterial blood pressure (ABP), not much is known about the intrinsic membrane properties of these neurons and their effect on cardiovascular function.The excitability of presympathetic PVN neurons is regulated by the integration of synaptic inputs with intrinsic membrane properties. Evidence for this is shown in PVN neurotransmitter systems that include GABA (30, 38), glutamate (9, 28, 31), nitric oxide (4, 20), and ANG II (7, 13, 29), which modulate the activity of presympathetic PVN neurons in vitro and SNA in vivo. One class of cha...

Sympathoexcitation in ANG II-salt hypertension involves reduced SK channel function in the hypothalamic paraventricular nucleus

“…Consistent with our previously published data (17), bilateral microinjection of the SK channel blocker apamin into the PVN markedly increased SSNA, RSNA, MAP, and HR in control rats fed a NS diet. Figure 1 shows representative raw tracings from a rat on a NS diet (left) before and after bilateral microinjection of apamin (12.5 pmol, 50 nl) into the PVN.…”

“…Figure 1 shows representative raw tracings from a rat on a NS diet (left) before and after bilateral microinjection of apamin (12.5 pmol, 50 nl) into the PVN. This dose of apamin has previously been shown to be the minimum dose to elicit a maximum ABP and SNA response in the PVN (17). Collectively (n ϭ 8), PVN-injected apamin increased SSNA (ϩ263.5 Ϯ 39.7%), RSNA (ϩ179.8 Ϯ 19.3%), MAP (ϩ36.7 Ϯ 4.4 mmHg), and HR (ϩ37.7 Ϯ 12.3 beats/min), as shown in the summary data in Fig.…”

“…Very recently, Pachuau et al (39) reported that diminished SK current contributed to the increased excitability of spinal IML-projecting PVN (PVN-IML) neurons in spontaneous hypertensive rats. Furthermore, our laboratory (17) has recently reported that blockade of SK channels in the PVN in normotensive rats substantially augments SNA and arterial blood pressure (ABP) in vivo. The present study was performed to determine if SK channel dysfunction is present in the PVN of anesthetized rats with ANG II-salt HTN.…”

Activation of the (pro)renin receptor in the paraventricular nucleus increases sympathetic outflow in anesthetized rats

“…Animal surgery was performed following the previously described protocol (13). Briefly, rats were anesthetized with an intraperitoneal injection containing a mixture of ␣-chloralose (80 mg/kg) and urethane (800 mg/kg).…”

“…With the use of a left flank incision, a left renal and splanchnic sympathetic nerve bundle was isolated from surrounding tissue (13,21,42), mounted on a stainless steel wire electrode (0.127-mm OD; A-M Systems), and covered with a silicon-based impression material (Light Body; Coltene) to insulate the recording from body fluids. The recorded signal was directed to an AC amplifier (P511; Grass Technologies) equipped with half-amplitude filters (band pass: 100-1,000 Hz) and a 60-Hz notch filter.…”