[Role of C-type natriuretic peptide receptor and large-conductance calcium-activated potassium channels in brain natriuretic peptide-induced porcine coronary artery dilation].

OBJECTIVE: To investigate the role of C-type natriuretic peptide receptor (NPR-C) and large-conductance calcium-activated potassium channels (BK(Ca)) in brain natriuretic peptide (BNP) induced porcine coronary artery dilation. METHODS: Porcine coronary artery rings were obtained and treated with BNP (10(-6) mol/L), BNP + NPR-C antagonist cANF4-28 (10(-6) mol/L) and BNP + BK(Ca) blocker tetraethylammonium (TEA, 1 mmol/L). The vascular tone experiments were observed on 10 vessel segments. BK(Ca) current density was measured by the whole-cell patch clamp technique. RESULTS: The maximum diastolic rate was similar between BNP group (68.51% ± 11.50%) and cANF4-28 + BNP group (65.67% ± 11.90%, P > 0.05) while significantly reduced in TEA + BNP group (28.87% ± 4.55%, all P < 0.05). When the holding potential was set at +60 mV, the BK(Ca) current density of BNP group was (78.48 ± 5.86) pA/pF, which was significantly higher than control group [(53.84 ± 4.55) pA/pF, P < 0.05], which was equally reduced in the TEA group and TEA + BNP group [(28.80 ± 2.76) pA/pF and (30.60 ± 3.88) pA/pF respectively, all P < 0.05 vs. control group]. CONCLUSION: BNP could relax the porcine coronary arterial smooth muscles by increasing BK(Ca) current, and this effect is not mediated by NPR-C.

[Sodium channel changes in human atrial cells isolated from various ages].

OBJECTIVE: To investigate if the increased incidence of atrial fibrillation with age was associated with changes of Na(+) channel in atrial myocytes. METHODS: Twenty-three patients underwent valve replacement operations were divided into adult [< 60 years, n = 15, 9 males, mean age (42.1 +/- 7.1) years] and aged group [> or = 60 years, n = 8, 5 males, mean age (63.3 +/- 3.1) years]. All patients were in normal sinus rhythm. Whole cell patch clamp techniques were used to record the Na(+) currents (I(Na)) of right auricle myocytes. RESULTS: Both current density and time-dependent recovery of I(Na) were similar in the cells from the 2 groups. Voltage-dependent inactivation of I(Na) of myocytes in the aged atria was shifted to more positive voltages. CONCLUSION: Current density of I(Na) was similar between the 2 age groups, and Na(+) channel might not be an important determinant for the increased incidence of atrial fibrillation in aged patients.

[Vasodilatory effects of CNP on aortic arteries of rabbits].

OBJECTIVE: To investigate the mechanism of vasodilatory effects of C-type natriuretic peptide (CNP). METHODS: Tension changes in aortic rings of rabbits were recorded with the presence of CNP or C-type natriuretic peptide receptor (NPR-C) agonist (cANF4-23) after pretreatment with epinephrine (NE) or 60 mmol/L KCl. The vasodilatory effects of four types of potassium channel blocker and NPR-C antagonist (cANF4-28) were also tested. RESULTS: A maximal vasorelaxant effects of (33.5 +/- 5.9) % and (38.4 +/- 10.6)% were recorded in the presence of 1 micromol/L CNP and cANF4-23, respectively, cANF4-28 attenuated the action of CNP [(19.8 +/- 8.3)%]. The vasorelaxant effects of CNP and cANF4-23 decreased significantly after pretreatment with 60 mmol/L KCl (P < 0.01). Glibenclamide and BaCl2 also attenuated the relaxant activities of CNP (P < 0.05). But only BaClZ decreased the vasodilatory action of cANF4-23 (P < 0.05). CONCLUSION: The relaxant activity of CNP is mediated through three paths: NPR-B/KATP, NPR-C/KIR and NPR-C/calcium channels.