The effect of noradrenaline on the ability of rat papillary muscle to resist an acute respiratory acidosis

Abstract

We have studied the effect of an increase in extracellular calcium and of noradrenaline on the ability of rat right ventricular papillary muscle in vitro to resist an acute fall in extracellular pH (pHe) produced by a rise in superfusate PCO2. We found a steep linear relationship, slope 0.86(SEM 0.06), r = 0.94, between a plot of logarithmic change in tension against pHe for control muscles (superfusate containing 1.8 mmol.litre-1 calcium). An increase in extracellular calcium (3.6 mmol.litre-1) increased absolute tension but did not alter the slope significantly. Increasing concentrations of noradrenaline (6.3 x 10(-8) to 6.3 x 10(-6) M) progressively reduced the slope of the tension/pHe plot from 0.82(0.05) to 0.35(0.07), p less than 0.001. Noradrenaline improved the ability of rat papillary muscle to resist an acute acidosis by a mechanism independent of changes in calcium concentration.