Effect of captopril on intracellular pH in vascular smooth muscle cells.

AIM: To observe the effect of captopril (Cap) on intracellular pH (pHi) in aortic smooth muscle cells (ASMC). METHODS: Cultured ASMC derived from rat and rabbit aortae were loaded with the fluorescent dye BCECF and pHi was determined using digital image processing method. RESULTS: The pHi of untreated SHR and WKY rats were 7.37 +/- 0.29 and 7.19 +/- 0.31, respectively. Oral Cap decreased pHi (7.11 +/- 0.26, P < 0.05) and exaggerated pHi response to angiotensin II (Ang-II, 0.1 mumol.L-1) in ASMC of SHR rats vs WKY rats (0.14 +/- 0.05 vs 0.21 +/- 0.05 pH units, P < 0.01). Cap in vitro had no effect on Ang-II induced intracellular alkalinization in ASMC of rabbits. CONCLUSION: Oral Cap inhibits Na+(-)H+ exchange activity in ASMC of SHR rats.

Effects of captopril and enalaprilat on intracellular Ca2+ content in isolated cardiomyocytes from rats.

AIM: To study the effects of ACEI captopril (Cap) and enalaprilat (Ena) on intracellular Ca2+ concentration ([Ca2+]i) in cardiac myocytes isolated from SHR and WKY rats. METHODS: Using fluorescent probe Fura 2-AM combined with computer image processing technique to measure [Ca2+]i. RESULTS: Resting [Ca2+]i was higher in SHR cardiac myocytes (174 +/- 5 nmol.L-1) than that in WKY rat myocytes (148 +/- 15 nmol.L-1, P < 0.01). Cap and Ena decreased the resting [Ca2+]i in SHR myocytes (161 +/- 11 and 166 +/- 7 nmol.L-1, respectively, P < 0.05) but not in WKY rat myocytes (P > 0.05). Both drugs inhibited [Ca2+]i increment induced by KCI, NE, or Ang II in SHR and WKY rat myocytes except on KCI-induced [Ca2+]i increment in WKY rat myocytes (P > 0.05). CONCLUSION: Cap and Ena had direct effects on pathological voltage-operated calcium channel in cardiac myocytes.

Effects of captopril and enalapril on intracellular Ca2+ in vascular smooth muscle cell.

AIM: To determine whether angiotensin-converting enzyme inhibitors can affect Ca2+ handling in cultured aortic smooth muscle cells (ASMC) directly. METHODS: Cultured ASMC derived from rat aorta were loaded with the intracellular Ca2+ ([Ca]2+i) fluorescent indicator Fura 2-AM and digital image processing technique was used. RESULTS: Resting [Ca2+]i was greater in ASMC from SHR vs WKY (P < 0.01). KCl-, norepinephrine (NE)-, and angiotensin II (Ang)-induced [Ca2+]i increases were enhanced in ASMC of SHR vs WKY (220 +/- 6, 212 +/- 8, and 215 +/- 14 vs 199 +/- 6, 202 +/- 7, and 195 +/- 7 nmol.L-1, respectively). Captopril (Cap) and enalapril (Ena) had no inhibitory effect on KCl-, NE-, and Ang-induced [Ca2+]i increases in ASMC of WKY. Cap and Ena inhibited KCl-, NE-, and Ang-increased [Ca2+]i in ASMC of SHR (210 +/- 7, 194 +/- 6, and 201 +/- 6 nmol.L-1, respectively). Ena and nifedipine similarly decreased KCl-, NE-, and Ang-increased [Ca2+]i. CONCLUSION: Cap blocked KCl-, NE-, and Ang-increased ([Ca2+]i) via a voltage-dependent Ca2+ channel of which function and specificity was altered in ASMC of SHR.

[Effects of guan-fu base A on spontaneous rate of isolated sinoatrial node of guinea pig].

Guan-fu base A (GFA) is a new alkaloid isolated from the tuber of Aconitum coreanum in our institute. Its effects on spontaneous electrical discharge rate of intact sinoatrial node preparations were investigated. Unipolar Ag-AgCl2 electrodes and DC-amplification were used to record unipolar electrograms from the endocardial surface of the isolated right guinea pig atria. GFA (4.29-214.5 micrograms/ml) decreased the spontaneous electrical discharge rate of sinoatrial node in a dose-dependent manner. The most effective concentration (214.5 micrograms/ml) of GFA resulted in sinus rate of 115 +/- 8 bpm (n = 7, control rate 208 +/- 13 bpm) within 30 min. Low external Ca2+ (0.18 mmol/L) enhanced the rate in lowering effect of GFA, in contrast with high external K+ (10.8 mmol/L) diminishing the effect of GFA. The ratios of IC30 of negative inotropic effects over IC30 of negative chronotropic effects were 9.38 for GFA and 1.73 for verapamil. GFA antagonized the positive chronotropic effect of isoproperenol but did not antagonize the positive inotropic effect of isoproterenol. The consequence of lowering sinus rate by GFA was not interfered by propranolol (0.15 micrograms/ml) or atropine (0.05 micrograms/ml). These results suggest that the bradycardia by GFA is a direct effect on sinoatrial node, but not due to the calcium channel block or beta adrenoceptor block.

Retinal toxicity in albino rabbits induced by intravitreal injection of strophanthin-K.

Time course and extent of strophanthin-K induced disturbances of flash electroretinogram (F-ERG) has been observed in 12 albino rabbits treated by a single dose of 1, 3 and 9 ug/0.1 ml of intravitreal injection. A phenomenon of the dependence of a- and b-wave amplitude changes on dosage was demonstrated. A 9 ug/0.1 ml dose caused a flat a- and b-wave showing the F-ERG wave could be completely suppressed by larger dose of strophanthin-K. Two parameters of "attenuation kinetics" are proposed to identify the pharmacodynamics and toxic kinetics on retina as time profile is concerned: 1) B (the slope of attenuation curve); 2) Et1/2 (half attenuative time). B and Et1/2 are helpful in making a tentative identification of the target cells on retina and in demonstrating a synergism or antagonism between drugs if any. The a-wave of F-ERG, having a steeper slope, is more sensitive than b-wave in terms of strophanthin-K toxicity bringing forth a quantitative criterion in visual pharmacology. The attenuation of amplitude in a-wave may therefore be considered as an early response to this drug. The direct pupillary response test were also done pre- and post-strophanthin-K, and the results of this test support that of F-ERG.

[Electrophysiological effects of changrolin on single ventricular myocytes isolated from adult guinea pig].

Calcium tolerant single ventricular cardiomyocytes were dispersed from adult guinea pig hearts by retrograde perfusion with collagenase solution. More than 50% of the isolated cells retained rod shaped configuration and showed normal electrical activities with resting potentials (RP) at -82 +/- 2 mV and action potential amplitude (APA) at 116 +/- 6 mV. The effects of changrolin (CRL, 4-[3', 5'-bis [(N-pyrrolidinyl)-methyl]-4'-hydroxyanilino]-quinazoline) on the transmembrane action potentials of the single cells were measured with intracellular glass microelectrodes. At the concentration of 50 mumol/L, CRL caused profound reductions of APA, maximal rate of phase 0 depolarization (Vmax), and action potential duration (APD). The effective refractory period (ERP) was prolonged. The action of CRL on Vmax showed use- and frequency-dependences. Trains of stimuli in the studied range of frequencies led to an exponential decline in Vmax to a new plateau and the maximal reduction was at the highest frequency. At 1 Hz, the onset rate of this action was 0.036 +/- 0.004 AP-1. CRL did not cause a resting state block of Vmax. These findings suggest that CRL is a slow type, class I anti-arrhythmia drug.

[Effects of guan-fu base A on fast response action potentials of papillary muscles of guinea pigs].

Guan-fu base A is a new alkaloid first isolated from the tuber of Aconitum coreanum in China. The electrophysiological effects of guan-fu base A were examined on the isolated papillary muscles of guinea pigs by glass-microelectrode technique coupled with microcomputer real-time analysis. Guan-fu base A 50 micrograms/ml had less effect on RP, but markedly decreased Vmax and APA of the fast response action potentials. The action potential duration was shortened at all voltage levels and plateau height was lowered. ERP was prolonged relatively and activation voltage became more negative. The inhibition of guan-fu base A on Vmax showed frequency dependent effects. The above results suggested that guan-fu base A could block the fast Na+ channels and exhibited anti-arrhythmic action.