In-vitro experiments performed in cat papillary muscles and strips of rat right ventricle suggest that the changes in myocardial contractility that follow acid-base disturbances are not a function of extracellular pH. Simultaneous changes in Pco 2 and NaHCO 8 concentration, with extracellular pH constant, decreased developed tension and maximal rate of rise of the tension (dT/dt) without significant changes in the time to peak tension when the muscle was exposed to the solution with higher Pco 2 and NaHCO 8 concentration. At an extracellular pH of 7.40, developed tension decreased 0.51 ± 0.13 g/mm 2 (P<0.02) and dT/dt decreased 1.29 ± 0.50 g/sec (P < 0.05) with no significant change in time to peak tension (0.038 ± 0.022 sec). Changes in pH produced by increasing Pco 2 at constant NaHCO 3 concentration were followed by a significant decrease in contractility. A change of Pco 2 from 20 to 90 Tnm Hg that produced a change in extracellular pH from 7.60 to 7.00 was accompanied by a decrease in developed tension of 0.67 ± 0.14 g/mm 2 (P<0.01), in dT/dt of 2.63±0.54 g/sec (P<0.01) with no changes in time to peak tension (0.0017 ± 0.10 seconds). We were unable to show significant variations in contractility when extracellular pH was changed at a constant Pco 2 of approximately 21 mm Hg (NaHCO 8 7.5, 15, and 30 DIM) or at a Pco 2 of approximately 95 mm Hg (NaHCO 3 15, 30, 60, 80 and 120 HIM). Only when extracellular pH reached a value as high as 8.0 (Pco 2 21 mm Hg, NaHCO 3 80 HIM) a small but significant increase in contractility was evidenced. Either Pcoj or intracellular pH could be the major determinants of the changes in myocardial contractility that follow acid-base alterations. gest that contractility is a function of external pH and independent of the way in which a change in pH took place. These authors concluded that the observed changes were most closely associated with external pH. Changes in P002 alone had no significant effect. On the other hand, Lorkovic (3), using an in-vitro preparation of isolated frog ventricular muscle, concluded that both intra-and extracellular pH play a role in the observed changes in contractility. It is difficult to ascertain whether the changes in cardiac performance observed in isolated blood-perfused hearts, heart-lung, or more intact preparations are due to variation in blood pH, Pco 2 , or both (3-10).Recent experiments in our laboratory on heart-lung preparations or perfused dog hearts have demonstrated that heart performance is affected by changes in Pco 2 but not by changes in pH when Pco 2 is kept constant (11).Considering the discrepancies between our results and those obtained with in-vitro preparations by other authors, experiments were undertaken on cat papillary muscles and strips of rat right ventricle to supply information about the effect of Pco 2 , pH, and NaHCO 3 concentration on mammalian ventricular contractility. Evidence will be presented that in changing ventricular contractility during extracellular pH alterations, the way in which a change in ex...
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.