[Downregulation of large conductance calcium-activated potassium channels in paraventricular nucleus contributes to sympathoexcitation in rats with chronic heart failure].

To elucidate the association between large conductance calcium-activated potassium channels (BK) in the paraventricular hypothalamic nucleus (PVN) and sympathetic outflow in rats with chronic heart failure (CHF) . Male Wistar rats (6-7 weeks old) were randomized to sham operated group and CHF group (coronary artery ligation) . Two weeks after operation, BK inhibitor Iberiotoxin (IBTX) was infused into PVN by osmotic minipumps, rats were divided into following groups: sham+aCSF, CHF+aCSF, sham+low dose IBTX (0.125 nmol/nl) , CHF+low dose IBTX, sham+moderate dose IBTX (1.25 nmol/nl) , CHF+moderate dose IBTX, sham+ high dose IBTX (12.5 nmol/nl) , and CHF+high dose IBTX (6 each) . Additional rats were grouped as follows: sham+vehicle, sham+KCNMB4 knockdown (by rAAV2-KCNMB4 shRNA virus injection in PVN) , CHF+vehicle, CHF+ KCNMB4 knockdown group (6 each) . The cardiac function was determined by echocardiography, left ventricular hemodynamics were measured invasively, renal sympathetic nerve activity (RSNA) was recorded at 6 weeks after coronary artery ligation or sham operation. The contents of norepinephrine (NE) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) in plasma were determined by enzyme-linked immunosorbent assay. The protein and mRNA expression of KCNMB4 in PVN were measured by immunofluorescence staining, Western blot, and real-time PCR, mRNA expression of BK in PVN was detected by real-time PCR. Compared with the sham operation group, the cardiac function of the heart failure group was significantly reduced (0.05) , and the plasma NE and the serum NT-proBNP were significantly elevated (0.05) . The protein and mRNA expression of KCNMB4 in PVN were obviously down-regulated in CHF rats (0.05) . After perfusion of IBTX or KCNMB4 knockdown by microinjection of rAAV2-KCNMB4 shRNA virus,right ventricular weight/body weight and lung weight/body weight ratio as well as left ventricular end-diastolic diameter were increased and left ventricular ejection fraction was decreased (all 0.05) , the sympathetic driving indexes was increased in sham rats, changes of these parameters further aggravated in CHF rats (0.05) . KCNMB4 knockdown further downregulated protein expression in PVN of CHF rats. Downregulation and blunted function of BK in PVN may contribute to sympathoexcitation and deterioration of cardiac function in rats with chronic heart failure.