Responsiveness to potassium and calcium ions of isolated cerebral arteries.

TODA, NOBORU. Responsiueness to potassium and cakium ions of isolated cerebral arteries. Am. J. Physiol. 227(5) : 1206-12 11. 1974.Dog cerebral arteries (basilar, posterior cerebral, and middle cerebral arteries) with an outside diameter of 0.3-0.5 mm were helically cut into strips so that responses to IS+ and Ca++ could be investigated. The addition of 5 mM K+ produced a transient relaxation, which was related directly to the tension developed by prostaglandin F2a. Similar relaxation was induced in basilar arteries from humans. The K-+-induced relaxation was dependent inversely on [K+]” and directly on the temperature of bathing media. The relaxing effect of K+ was attenuated by ouabain and abolished by substitution of LiCl for NaCl. Cerebral arterial strips when soaked for 60 min in Ca +-+-free media and treated with high concentrations of K+ showed triphasic responses to Ca++ (2.2 mM), rapid contraction, rapid relaxation, and slow, sustained contraction. When K+ was not added prior to Ca++, only a rapid contraction followed by relaxation was induced. The relaxation was increased by treatment with EGTA in combination with exposure to Ca ++-free media. Treatment with ouabain and substitution of LiCl for NaCl abolished the relaxation in response to Ca++ in the K+-treated preparations and fused the rapid and slow contractions into one. It may be concluded that relaxation of cerebral arteries induced by K+ in normal K+ solutions is due to stimulation of the electrogenic Na+ pump and that relaxation following the rapid contraction induced by Ca++ in the arteries exposed to Ca $-+-free media is associated either with a rapid uptake of Ca ++ by sarcop lasmic reticulum or with an active Ca++ extrusion mechanism.