Action and interaction of perivascular H+, K+ and Ca++ on pial arteries.

In cats the perivascular space of small pial arteries was perfused with mock CSF by means of micropipettes. Variations of K+, H+ and Ca++ activities in the perfusate cause changes of the diameters of the affected vessels. Increases of H+ and moderate increases of K+ lead to dilatations, Ca++ -increases elicit constrictions. The ions interact in such a way that perivascular Ca++ inhibits the K+ or H+ induced dilator response of the pial arteries. Alkalosis intensifies the constrictor action of Ca++. Perivascular microperfusion with Ca++ -free mock CSF causes dilatation which can be augmented by additional acidosis (pH 6.5). However, an increase of K+ to 10.8-10(-3) mol.1(-1) (4 times normal) does not change the diameters of the vessels already dilated, thus indicating differences in the action of K+ and H+ upon the membranes of the pial vascular smooth muscle cells. Small vessels (less than 80 micron diameter) respond with a significantly stronger dilatation when Ca++ is complexed with EGTA as compared with vessels of more than 80 micron diameter.