After reviewing recent experimental work from various laboratories we have come to the following conclusions. (1) An increase in transmural pressure causes depolarisation of coronary arterioles, which increases smooth muscle tone. Under these conditions the opening of KATP channels can induce a much larger change in membrane potential than in relaxed arteries. Furthermore, the rate of ATP hydrolysis by contractile proteins, and thus the submembrane nucleotide concentrations, might also be changed in the presence of myogenic tone. Therefore care should be taken when extrapolating patch clamp results from isolated coronary smooth muscle cells to the function of KATP channels in vivo. (2) The opening of KATP channels is increased in situations related to energy imbalance, such as hypoxia, adenosine release, intracellular acidification, and lactate accumulation. However, there is increasing evidence that KATP channels also contribute to the setting of the membrane potentials of coronary smooth muscle cells under normoxic conditions. Thus the modulation of KATP channels by intracellular metabolites and by vasoactive autacoids may play an important role in the regulation of coronary blood flow even in the presence of normal intracellular ATP concentrations. (3) The smooth muscle cells of coronary terminal arterioles form an electrical syncytium. The opening of a new KATP channels in smooth muscle cells of a terminal arterioles might induce a spatially homogeneous hyperpolarisation of the entire arteriole. The resulting homogeneous decrease in the tone of the coronary smooth muscle cells of the arteriole may induce a considerable change in vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)