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 [Ki] and of the [Ki]:[Ko] ratio varied in opposite directions. During prolonged storage at 4°C the artery strips lost K and their ability to respond to stimuli. Subsequently they were transferred to recovery solutions of various [Ko] at 38°C. The initial rate of Ki reaccumulation and steady state [Ki] were greater in solutions of higher [Ko]. Conversely for any time during recovery, the greater [Ko], the smaller the [Ki]:[Ko] ratio. When the strip was placed in the warm recovery solution it first contracted and then relaxed. The initial contraction was not relatable to [Ko] of the recovery solution but the subsequent relaxation was greater in rate and magnitude as [Ko] was greater. As the muscles recovered further they went into tonic contracture. As the [Ko] 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 [Ki]:[Ko] ratio and [Ki]. Conclusions drawn were: (a) increased [Ki] increases contractility, (b) increased [Ki] increases the rate of relaxation, (c) excitability is decreased by too high or low a [Ki]: [Ko] ratio, and (d) the extent of tonic shortening depends on the [Ki]:[Ko] ratio.

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Copyright ©, 1963, by The Rockefeller Institute Press
1962
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