Increased flow rate and papaverine increase K+ exchange in perfused rat hind-limb skeletal muscle

This study tested the hypothesis that increases in perfusate flow rate resu lt in increased rates of unidirectional and net K+ transport in rat hind-li mb skeletal muscle at rest. Ten neurally and vascularly isolated hind limbs , with arterial and venous catheters placed proximal to the popliteal regio n, were perfused for 10-min periods at flow rates (presented in a random or der) of 0.27, 0.42, 0.63, 0.84, or 1.05 mL.min(-1).g(-1). Potassium extract ion and unidirectional Kf influx were determined using K-42, and arterial p erfusion pressure was measured continuously. Increases in flow rate resulte d in decreases in K+ extraction and increases in unidirectional K+ influx, unidirectional K+ efflux. and net K+ efflux. The increases in K+ flux were associated with increases in oxygen uptake, glucose uptake, acid lactate re lease. In separate experiments (n = 5), the vasodilator papaverine (10(-4) M) did not further vasodilate the vasculature of resting hind limbs, sugges ting that the hind limbs in this preparation were fully vasodilated. Papave rine, at constant flow, resulted in a nearly 1.5-fold increase in K+ extrac tion, a doubling of unidirectional K+ influx, and increases in unidirection al K+ efflux and net K+ efflux. It is concluded that physiological increase s in flow rate result in increases in K+ transport in isolated, perfused ra t hind-limb skeletal muscle. Furthermore, papaverine appeared to induce an increase in skeletal muscle membrane permeability to K+.