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00005768-200305001-0051500005768_2003_35_s93_kahn_interstitial_5miscellaneous< 19_0_5_0 >Medicine & Science in Sports & Exercise©2003The American College of Sports MedicineVolume 35(5) Supplement 1May 2003p S93VASTUS LATERALIS INTERSTITIAL POTASSIUM RISES WITH TILT IN HUMANS[B-13O FREE COMMUNICATION/POSTER SKELETAL MUSCLE METABOLISM]Kahn, M1; Leuenberger, U A.1; Sinoway, L I.1; MacLean, D A.11Penn State University, Hershey Medical Center, Hershey, PA and Exercise Science, Kent State University, Kent, OH(Sponsor: Ellen L. Glickman, FACSM)The myogenic response is the inherent ability of blood vessels to respond to changes in transmural pressure. At the cellular level, the myogenic response is characterized by two important electrophysiological responses to a rise in transmural pressure: 1) an increase in the rate of action potential firing, and 2) a rise in resting membrane potential (RMP). The RMP is determined largely by the K+ concentration gradient across the cell membrane and thus the RMP can be estimated from the Nernst equation. When humans stand, lower extremity transmural pressure increases and it has been suggested that this evokes a myogenic vasoconstrictor response in the legs, which may play an important role in preventing orthostatic hypotension.PURPOSETo examine the effects of head-up tilt on skeletal muscle interstitial K+ concentrations measured in the thigh.METHODSEight healthy subjects underwent 60 ° head-up tilt for 20 minutes or until they developed orthostatic symptoms.RESULTSTilt increased (P < 0.05) transmural pressure (92.6 ±6.6 vs. 152.3 ±10.1 mmHg), interstitial K+(5.44 ±0.41 vs. 7.93 ±0.65 mM) and RMP (−86.5 ±1.8 vs. −76.7 ±2.1 mV). In addition, transmural pressure correlated with RMP (r = 0.540, P < 0.05).CONCLUSIONThese data illustrate that tilt increases transmural pressure, which correlated with the increase in RMP, suggesting that as transmural pressure rises, the myogenic response is engaged.VASTUS LATERALIS INTERSTITIAL POTASSIUM RISES WITH TILT IN HUMANSKahn, M; Leuenberger, U A.; Sinoway, L I.; MacLean, D A.B-13O Free Communication/Poster Skeletal Muscle Metabolism535