Increasing the basic stimulation rate or calcium concentration in guinea-pig atria primarily increased the size of parameter A in the mechanical restitution exponential function.
The restitution of peak force and post-extrasystolic potentiation in guinea-pig and rat atrial muscle can be described by exponential functions, suggesting the presence of two separate intracellular compartments for activator calcium.
Isometric force and action potentials were recorded in thin atrial strips from guinea-pigs and rats (32 degrees C). The restitution of peak force and action potential duration, after a regular contraction, was determined (test interval 0.1-120 s), together with the post-extrasystolic potentiation. The mechanical restitution could be described with an exponential function in two phases as: force = A(I-e-k1t) + B(I-e-k2t). By increasing the basic stimulation rate in guinea-pig atria from 0.2 to 2 Hz, the size of A was approximately doubled while B was only slightly affected. When Ca2+ was increased from 0.9 to 3.6 mmol l-1, the size of A increased approximately 3.4 times while B decreased only slightly. There was a close correlation between steady-state contractility of the muscle and parameter A but not parameter B. In a similar fashion post-extrasystolic potentiation can be described as: force = Ce-kt + D. This potentiation was greater in guinea-pig than in rat hearts. In both species the rate of potentiation decay (k) was usually similar to the rate of the first phase of restitution (k1). It seems reasonable to interpret the parameters A and B as reflections of two separate intracellular compartments for activator calcium.
JÓHANNSSO et al. (Wed,) reported a other. Stimulus interval changes and calcium concentration increases vs. Baseline stimulation was evaluated on Restitution of peak force and action potential duration, and post-extrasystolic potentiation. Increasing the basic stimulation rate or calcium concentration in guinea-pig atria primarily increased the size of parameter A in the mechanical restitution exponential function.