Evidence for a carbachol stimulated phosphatidylinositol effect in heart

Incubation of canine heart slices with 32P-inorganic phosphate in physiological medium resulted in the incorporation of 32P into a number of cardiac phospholipids. Carbachol, a non-hydrolyzable acetylcholine analogue, selectively increased 32P-incorporation into phosphatidic acid and phosphatidylinositol in slices of right auricle 80 and 70% respectively. This effect of carbachol was half-maximal at 5-10 microM and was inhibited completely by atropine. Carbachol did not affect labeling of other phospholipids in right auricle and did not affect the labeling of any phospholipid in slices of left auricle or right or left ventricle. These results provide evidence for a muscarinic receptor mediated phospholipid effect which appears to be localized in the right atrial region of canine heart.