Abstract
A comparison of the effects of Ca and epinephrine on contractile tension changes and Ca45 exchange in isolated rabbit atria was made. Dose response curves of Ca were determined with and without epinephrine (2.7 x 10–5 m) and dose response curves of epinephrine were determined with three concentrations of Ca in the media (0.3 mm, 2.4 mm and 9.6 mm) at both pH 6.9 and pH 7.75. Epinephrine enhanced the effect of a given concentration of Ca two to three times in a competitive manner. However, Ca acted as a noncompetitive inhibitor on the response of atria to epinephrine. Ca45 studies revealed that epinephrine decreased Ca influx. This effect was enhanced by increasing the extracellular Ca concentration. Ca45 efflux was not affected by epinephrine. Increasing the pH acted similar to epinephrine. These data suggest that epinephrine increases contractile strength of the heart by at least two mechanisms, one involving an increased binding of calcium in the membrane (competitive), the other involving a noncompetitive antagonism, perhaps of another essential component in the reaction, such as Mg++.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
