Possible mechanisms of inhibitory action of protamine on contractile activity of rat aorta.
Experiments were performed to determine possible mechanisms of inhibitory action of protamine chloride on noradrenaline (10 microM)-, KCl (40 mM)-, BaCl2 (1 mM)- and CaCl2 (10 mM)-induced contractions in rat aorta. Protamine, La3+ and gallopamil (D600), inhibited the K+-induced contractions more effectively than the noradrenaline-induced responses on the basis of the concentrations giving 40% inhibition. Lanthanum (1-5 mM) reduced tissue Ca content in both normal and Ca2+-depleted Tris-buffered solutions and produced an increase in 45Ca efflux from the aortic strip into the Ca2+-depleted Tris solution. Protamine (1-5 mg ml-1) reduced tissue Ca content in normal Tris solution, but to a lesser extent than La3+ in the Ca2+-depleted solution. Furthermore, protamine (3 mg ml-1) produced no increase in 45Ca efflux from aorta. These results suggest that protamine chloride may preferentially inhibit the Ca2+ influx stimulated by K+ depolarization and that its inhibitory action on rat aorta may be due to non-specific displacement of the superficially located bound Ca2+ of the cell membrane, which can also be readily removed by treatment with Ca2+-depleted solution.
Uruno
T
T
Matsumoto
R
R
Okushita
K
K
Sunagane
N
N
Kubota
K
K
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D001464:Barium / Q000494:pharmacology; D017609:Barium Compounds; D002118:Calcium / Q000378:metabolism; D002122:Calcium Chloride / Q000494:pharmacology; D002712:Chlorides; D004347:Drug Interactions; D005711:Gallopamil / Q000494:pharmacology; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011479:Protamines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D017609:Barium Compounds; D002712:Chlorides; D011479:Protamines; C024986:barium chloride; D001464:Barium; D005711:Gallopamil; D011189:Potassium Chloride; D007811:Lanthanum; D002122:Calcium Chloride; D002118:Calcium; D009638:Norepinephrine