Modification of myogenic intrinsic tone and [Ca2+]ii of rat isolated arterioles by ryanodine and cyclopiazonic acid

Abstract

The role of the sarcoplasmic reticulum (SR) in regulating myogenic tone and [Ca2+]i was examined with ryanodine and cyclopiazonic acid (CPA) in the rat skeletal muscle arteriole (Ask) and mesenteric arteriole (Ams). Arterioles were cannulated at both ends to control luminal pressure in a tissue bath. Luminal diameter was measured with a video-monitored microscopic system. Fura 2-AM was loaded to measure [Ca2+]i using the fluorescence intensity ratio at excitation wavelengths of 340 to 380 nm (F340/380). The myogenic response (luminal pressure was increased from 40 to 100 mm Hg) and the intrinsic tone at 40 mm Hg were observed in Ask but not in Ams. Ryanodine (10-5 M) decreased the steady-state diameter of Ask from 138±8 to 85±9 μm (P