ISSN:
1573-8221
Keywords:
papaverine
;
isoprenaline
;
La3+
;
compound D-600
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract Experiments on strips of guinea pig taenia coli were carried out by the double sucrose gap method. Isometric contractions of the strip in the region of the artificial node were recorded during perfusion with a solution containing a high concentration of potassium (120 μM KCl, 47mM NaCl), to which one of the myolytics and agents inducing contraction of depolarized muscle were successively added. “Off-responses” (OR) arising after the end of stimulation by square hyperpolarizing pulses (11 sec) also were studied. D-600 (10−5 g/ml) and La3+ (2·10−4 g/ml) were shown to reduce muscle tone (residual potassium contracture) and to abolish the contractile effects of histamine or of a tenfold increase in the Ca2+ concentration in the medium [Ca]0. The amplitude of OR fell but its kinetics remained unchanged. Papaverine (10−5 g/ml) caused a lasting decrease in tone, abolished the effects of an increase in [Ca]0 or addition of histamine, but caused virtually no change in the amplitude of OR — the only effect was a sharp increse in the rate of muscle relaxation after the end of its contraction phase. Isoprenaline (10−6 g/ml) lowered the tone of the depolarized muscle without changing the contractile effects of histamine, an increase in [Ca]0 or OR. The results point to differences in the mechanisms of action of the various myolytics. D-600 and La3+ block chemically excitable and all types (fast, slow, and uninactivated) of electrically excitable Ca channels. The action of isoprenaline is evidently connected with activation of the system of cyclic AMP synthesis and, consequently, with increased sequestration of Ca2+ in the intracellular depots. To understand the nature of the action of papaverine, it has to be suggested that it can block chemically excitable Ca channels and also electrically excitable Ca channels that have been open for a long time.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00801390
