The Role of Extracellular Cations in the Development of Myogenic Contraction in Isolated Rat Small Arteries

The purpose of this study was to determine the roles of extracellular cations (Na+, Ca2+ and K+), membrane K+ channels and Na+/K + ATPase in the development of myogenic contraction (transmural pressure-induced contraction) in isolated rat skeletal muscle and mesenteric small arteries. The vessels were pressurized under no-flow conditions in a tissue bath. Lumen diameter was measured with a videomicroscopic system. Myogenic contraction was evoked by increasing the lumen pressure from 40 to 100 mmHg. The vessels demonstrated myogenic contraction in low-Na+ (Na+ 1.18 mmol/L) physiological salt solution (PSS), and this was abolished by removing Ca2+ or by applying nifedipine or nisoldipine (10 μmol/L). Neither tetraethylammonium (TEA, 1 mmol/L), Ba2+ (10 μmol/L) nor glibenclamide (1 μmol/L) affected the magnitude of the myogenic contraction. K+-free PSS and ouabain (0.1 mmol/L) partially depressed myogenic contraction. In conclusion, myogenic contraction was triggered by a cellular process that requires extracellular Ca2+, but not Na+ or K+. This triggering process is not affected by TEA, Ba2+ or glibenclamide. (Jpn Circ J 1996; 60: 239 - 246)