ABSTRACT
The identity o f endothelium-dependent hyperpolar iz ing factor ( E D H F ) still remains the subject o f considerable controversy. In addi t ion to a diffusible factor, electrical coup l ing between the endothel ium and the smooth muscle cells cou ld contribute to the E D H F response to a variable extent i n different arteries. However , i n spite o f an increasingly complex picture, there are aspects o f the pathway wh ich are bo th clear and apparently universal . P robab ly the most significant o f these is the fact that act ivat ion can be b locked in the combined presence o f the potassium channel toxins apamin and charybdotox in ( W a l d r o n and G a r l a n d , 1994; C o r r i u et al, 1996). Other related facts are that an essential early step i n the act ivat ion o f a l l endothel iumdependent d i la tor pathways is an increase i n the endothelial cell ca lc ium concentra t ion , and that this increase i n ca lc ium is associated wi th a hyperpolar iza t ion o f the endothelial cell membrane (Busse et al, 1989; C h e n and Suzuk i , 1990; Plane et al, 1998).
