Papaverine stimulates K+ turnover in resting rat hindlimb skeletal muscle

The purpose of this study was to describe the stimulation of K' turnover by papaverine (PAP) in resting skeletal muscle. Rat hindlimbs (n=5) were perfused for 20 min followed by 20 min with 10"5 M PAP. The perfusate contained bovine red blood cells, artificial plasma and 42K. Blood samples were analyzed for gases, ions, glucose, lactate, and 43K activity. Perfusate flow, arterial perfusate pressure and resting muscle tension were constant throughout the protocol. PAP increased (p<0.05) unidirectional K* uptake (JinK*) (0.280±0.038 and 0.417±0.073 umolg 'min'1 at 1,5 and 8.5 min of PAP respectively) compared to baseline (0.204±0.070) . The initial increase in JinK* was associated with a non-significant net uptake of K* (JnetK') compared to baseline (0.12±0.03 vs. 0.03 tO. 004 umol'g'min"1) . JnetK* decreased (-0.017 ±0.008 umolgmin"1) at the end of perfusion indicating an almost 2-fold increase in unidirectional K* efflux. Associated with these changes were increased net glucose uptake and a net lactate efflux from the muscle. Net Na* and Cl fluxes did not change. It is concluded that PAP stimulated K' influx and K* efflux in resting skeletal muscle independent of changes in muscle perfusate flow, perfusion pressure and vascular resistance.