On the contractile function of protein phosphatases in isolated human coronary arteries

It is unknown whether protein phosphatases types 1 and 2A are present in an d can regulate the tone of human vascular tissue. The expression and possib le function of serine/threonine protein phosphatases (PP) type (PPI) and ty pe 2A (PP2A) were studied in isolated human coronary arteries. Catalytic su bunits of PP1 and PP2A were identified by means of phosphatase activity mea surement in tissue homogenates, by separation of enriched extracts through affinity column chromatography, by immunoblotting with specific antibodies, by hybridization of mRNA with specific DNA probes and PCR of reverse trans cribed mRNA. Based on these methods. the catalytic subunits of PP1(alpha,be ta,gamma) and PP2A(alpha,beta) were identified. Appropriately, cantharidin, an inhibitor of PP1 and PP2A, increased basal tone of human isolated coron ary artery rings with an EC50 of about 16 mu mol/l by increasing the phosph orylation state of the regulatory light chains of myosin. In summary, PP1 a nd PP2A are ex pressed in human coronary arteries and they can alter vascul ar tone.