AJP - Cell Physiology, Vol 252, Issue 2 C248-C252, Copyright © 1987 by American Physiological Society
Negative inotropic effect of extracellular calcium buffering in cardiac muscle
Y. Shimoni and S. Ginsburg
Heart muscle contracts more vigorously when calcium levels are raised. A
transient depletion of calcium from restricted extracellular spaces occurs
with each contraction. We decided to maintain the concentration of this ion
at a constant level by using an external calcium buffering system. It was
found that buffering calcium at a millimolar level (using citrate as a
buffer) caused a decrease, rather than an increase in the strength of
contraction. The mean reduction in peak tension was by 27% in guinea pig
and by 50.5% in frog atrium. This finding is analyzed; its most plausible
explanation is the hypothesis that the buffer dissipates a calcium
inhomogeneity, consisting of a higher calcium concentration adjacent to the
membrane. Alternative interpretations such as intracellular acidosis, were
tested experimentally and ruled out.
