Potassium and the recovery of arterial smooth muscle after cold storage.

The influence of K on the performance of vascular smooth muscle was studied by observing the mechanical performance of the muscle under conditions in which the magnitudes of [K(i)] and of the [K(i)]:[K(o)] ratio varied in opposite directions. During prolonged storage at 4 degrees C the artery strips lost K and their ability to respond to stimuli. Subsequently they were transferred to recovery solutions of various [K(o)] at 38 degrees C. The initial rate of K(i) reaccumulation and steady state [K(i)] were greater in solutions of higher [K(o)]. Conversely for any time during recovery, the greater [K(o)], the smaller the [K(i)]:[K(o)] ratio. When the strip was placed in the warm recovery solution it first contracted and then relaxed. The initial contraction was not relatable to [K(o)] of the recovery solution but the subsequent relaxation was greater in rate and magnitude as [K(o)] was greater. As the muscles recovered further they went into tonic contracture. As the [K(o)] in the recovery solutions was greater these contractures occurred after shorter recovery times, and attained greater amplitude at a faster rate. Solution-switching experiments indicated a dependence of responses to electrical shocks on both the [K(i)]:[K(o)] ratio and [K(i)]. Conclusions drawn were: (a) increased [K(i)] increases contractility, (b) increased [K(i)] increases the rate of relaxation, (c) excitability is decreased by too high or low a [K(i)]: [K(o)] ratio, and (d) the extent of tonic shortening depends on the [K(i)]:[K(o)] ratio.