The effects of EGTA on vascular smooth muscle contractility in calcium-free medium.
The effect of EGTA, commonly present in Ca2+-free physiological saline solution, on the contractile responses induced by Ca2+ and phenylephrine was studied in dog mesenteric arteries and aortas of rats and rabbits. EGTA substantially enhanced the contractile responses of these vascular strips or rings to added Ca2+ after a prolonged preincubation period in the Ca2+-free medium. The maximal level of the enhanced contractile responses was independent of EGTA concentration, but the rate of the maximal responses was faster at higher EGTA concentration, presumably as a result of faster removal of intracellular Ca2+. Such a Ca2+-induced response was sensitive to the Ca2+ antagonist, nifedipine. EGTA present at low concentrations (50 and 400 microM) in Ca2+-free medium also inhibited the phenylephrine-induced contractile response more prominently for the longer preincubation periods of the vascular tissues in Ca2+-free medium. Our results suggest that EGTA, even when added at low concentrations to the vascular smooth muscle for a sufficiently long period in Ca2+-free medium, may cause destabilization of the cell membranes leading to increased permeability to subsequently added Ca2+. EGTA may also remove the superficially bound Ca2+ and subsequently reduce the intracellular Ca2+ pool via extraction of the intracellular Ca2+ at the cell membrane surfaces.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003470:Culture Media; D004285:Dogs; D004533:Egtazic Acid / Q000494:pharmacology*; D008638:Mesenteric Arteries / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D013997:Time Factors; D015016:Yohimbine / Q000494:pharmacology
D003470:Culture Media; D010656:Phenylephrine; D015016:Yohimbine; D004533:Egtazic Acid; D009543:Nifedipine; D002118:Calcium; D011224:Prazosin