SUMMARYBecause of the reported presence of a Na+-Mg2' exchanger in guinea-pig but not in ferret myocardium, the Mg2+ extrusion mechanism in guinea-pig myocardium has been reinvestigated using Mg2+-and Na+-selective microelectrodes and the fluorochromes mag-fura- In vitro calibration of mag-fura-2 and -5 using the ratio method gave values for Kd (experimentally determined dissociation constant) of 22 2 + 2-7 (mean + S.D., n = 7) and 25-7+ 1 3 (n = 4) mmol/l respectively. Mag-fura-2 reacted to physiological concentrations of Ca2+ and mag-fura-5 to changes in pH. In isolated myocytes, Na+ removal gave an apparent increase of [Mg2+], with mag-fura-2 but not with mag-fura-5. However, when the pH, was altered with NH4Cl mag-fura-5 showed an apparent decrease in [Mg2+]i on application and an apparent increase on removal, with a time course similar to the pH, changes. It is concluded that Mg2+ extrusion in guinea-pig myocardium is not via a Na+-Mg2+ exchanger. The use of mag-fura-2 and -5 are limited in their application because of Ca2+ and H+ sensitivity respectively.
directly assess these functional changes. These findings were correlated with data obtained by more classical indirect methods and further delineate the concept of a reversible alteration in membrane transport and are consistent with an in vivo swelling of skeletal muscle cells in response to severe hemorrhagic shock.
Methods and MaterialsNon-splenectomized adult baboons (Papio Sp.) weighing 12-27 Kg. were anesthesized initially with a combination of intravenous Sernylan (1 mg./Kg.) and Pentobarbital (5 mg./Kg.) and maintained on small doses of Pentobarbital throughout the experiment to achieve a constant level of anesthesia. Tracheostomy was performed. Polyethylene catheters were used to cannulate the femoral artery of one leg and femoral vein of the opposite limb. Arterial pressure was constantly. mdnitored on a Sanborn recorder connected to the femobral artery cannula through a pressure transducer. Blood samples for all analyses were obtained from the femoral artery cannula and all injections were given through the femoral vein catheter.Each animal was studied throughout a standard 3-hour control period and then following induiction of hemorrhagic shock. Arterial pressures of 60 mm. Hg systolic were achieved during the first 8-10 minutes of hemorrhage and subsequent hemorrhage was carried out as needed to maintain this level of hypotension. Care was taken to avoid hemorrhage in excess of 25-30% of calculated blood volume in order to obtain a prolonged severe shock preparation. Serial determinations of skeletal muscle PD as well as blood pressure, pulse, and respiration were recorded 288Presented at the Annual Meeting of the American Surgical Association,
Rapid infusion of moderate volume of isotonic saline improved survival in uncontrolled hemorrhage. Extreme volumes, infused rapidly, also resulted in higher survival rates compared with those observed in nonresuscitated rats.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.