Effects of cooling and rewarming on Na, K, and tension changes in rat tail artery

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Abstract
The relation of cell Na and K to vascular smooth muscle tension was studied in the isolated, perfused rat tail artery. Glass electrodes were used to measure ion exchanges; cooling and rewarming were used to modify cell ion content and exchange rates. The cells, made Na-rich and K-poor by overnight cooling of the artery at 2 °C, responded weakly to vasoactive agents (norepinephrine, L-8 vasopressin, and angiotensin) and characteristically showed a slow rate of rise followed by a still slower rate of fall in tension. Within minutes of initiating rewarming to 37 °C the rate of rise was accelerated even in the presence of metabolic inhibitors. The degree of rise depended on the degree of restoration of ionic gradients; it increased progressively with the time allowed for extrusion of Na and reaccumulation of K, a process which could be blocked by iodoacetate. During rewarming, the Na/K exchange rate rose from zero at 2 °C to reach a maximum toward the end of the first hour of rewarming, and in this interval the rate of relaxation following stimulation returned to normal. Stimulation of the cold artery with angiotensin enhanced subsequent Na outflow during rewarming without affecting K inflow, and the tissue was unable to respond to a second stimulus.