Frequency-dependence of Vmax in K-depolarized guinea pig ventricle: effects of nifedipine and verapamil
| Autor: | Theodore C. West, James P. Woods |
|---|---|
| Rok vydání: | 1985 |
| Předmět: |
Male
medicine.medical_specialty Nifedipine Guinea Pigs Diastole In Vitro Techniques Guinea pig Internal medicine medicine Animals Pharmacology Chemistry Depolarization Heart Frequency dependence Electric Stimulation Electrophysiology Kinetics medicine.anatomical_structure Endocrinology Verapamil Ventricle Potassium Cardiology and Cardiovascular Medicine medicine.drug |
| Zdroj: | Journal of cardiovascular pharmacology. 7(1) |
| ISSN: | 0160-2446 |
| Popis: | Right ventricular strips from guinea pig hearts were used to compare the effects of nifedipine and verapamil on the maximal upstroke velocity (Vmax) of rapid depolarization in potassium-depolarized preparations. The Vmax was used as an indirect measure of the slow inward current (Isi). Barium (0.8 mM) was added to the Tyrode solution to restore excitability of the K-depolarized tissue. The effects of nifedipine and verapamil on rested state Vmax (VmaxRS), frequency-dependent changes in Vmax, and recovery of Vmax as a function of diastolic interval were studied. The depression of Vmax at rested state (RS), following 3-5-min rest, was concentration-dependent for both drugs, although the effect of nifedipine was greater. The percentage depression of VmaxRS by nifedipine was 24.3 +/- 6.4 at 10(-8)M, 51.3 +/- 2.6 at 5 X 10(-8)M, and 74.0 +/- 1.0 at 10(-7)M. For verapamil the values were 6.2 +/- 3.8 at 10(-7)M, 13.1 +/- 0.9 at 5 X 10(-7)M, and 42.0 +/- 0.5 at 10(-6)M. The depression of Vmax by each drug was frequency-dependent over a range from 0.05 to 2.0 Hz. Frequency-dependence was quantitatively greater with verapamil. The kinetics of recovery of Vmax were assessed by means of paired stimuli given at varying diastolic intervals during recovery from a RS depolarization. The recovery curve was biexponential. In the drug-free condition, the time constant for the first phase of recovery (Tr1) was 140 +/- 12 ms and the time constant for the second phase (Tr2) was 2689 +/- 146 ms.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|