EFFECTS OF EXTRAVASCULAR ACIDIFICATION AND EXTRAVASCULAR ALKALINIZATION ON CONSTRICTION AND DEPOLARIZATION IN RAT CEREBRAL ARTERIOLES IN-VITRO

The relationship between cell membrane potential, vessel diameter, and pH in small cerebral arterioles is not completely understood. This st udy involved direct, simultaneous measurement of cell membrane potenti al and vessel diameter at various extracellular pH levels. Arterioles ranging from 44 to 91 mu m in diameter were isolated, transferred to a temperature-controlled microscope chamber, which was used as an organ bath, and observed through an inverted videomicroscope. Two Vessel ca nnulation procedures were used: a single-sided cannulation with the ot her side occluded, and a double-sided and perfused cannulation. After cannulation, the vessels were pressurized to 60 mm Hg intraluminally a nd the bath temperature was raised to 37 degrees C. Cell membrane pote ntials of vessel wall cells were obtained after the bath temperature r eached 37 degrees C with the vessels partly constricted and again afte r spontaneous tone (constriction) of the healthy vessels had developed . The effect of extraluminal pH on cell membrane potentials was studie d by changing the bath pH from 7.3 to either 7.65 or 6.8 in the single -sided cannulation. The average cell membrane potential for vessels at 37 degrees C, with 60 mm Hg of intraluminal pressure and pH 7.3, was -37.5 mV. The cell membrane potential depolarized to -30.9 mV at pH 7. 65 and hyperpolarized to -58.4 mV at pH 6.8, with a slope of 25.8 mV/p H unit. The effect of depolarizing extracellular potassium ions on the cell membrane potential was examined by perfusing two vessels with mo dified Ringer's solution containing 70 mM KCl. This perfusion method d ecreased the vessel diameter by 48% and depolarized the observed cell membrane potential from -41.9 to -19.8 mV, with a slope of -0.42 mV pe r percentage diameter change. These data provide the first measurement s of membrane potentials of isolated penetrating arteriole wall cells is vitro. The results indicate that the cell membrane potential relate s linearly to the vessel diameter. This new technique opens the possib ility for studying vessel response to stimuli under controlled conditi ons and regulatory mechanisms such as the propagation of vasomotor res ponses.