Immunohistochemical localization of adenylyl cyclase isoforms in articular chondrocytes of rat

Adenylyl cyclase (AC), the enzyme of synthesis of the 2nd messenger cAMP, mediates signal transduction in response to external stimuli through coupling to G proteins. To date, mammalian cells are known to express ten different AC isoforms with individual pharmacology and tissue distribution. Identity of AC isoforms in articular chondrocytes is not well established. We employed immunohistochemistry to identify and localize AC isoforms in rat articular chondrocytes. Tissues known to express AC isoforms were used as positive controls. For negative controls primary antibody was preabsorbed with the control peptide. Articular chondrocytes were distinguishable into superficial, middle and deep zones and exhibited variable immunoreactivity. In the superficial zone chondrocytes were smaller and weakly immunoreactive for all the isoforms. In the middle zone, staining for AC I and III was intense and moderate immunoreactivity was observed for AC II and IV. Chondrocytes in the deep zone were large in size. Moderate immunoreactivity for AC II was detected in the deep zone. Chondrocytes were weakly immunoreactive for AC isoforms V / VI in all three zones. Our preliminary results indicate grouping of expressed AC isoforms, potentially predicting the pharmacology of cAMP‐mediated signal transduction. (Results of AC VII – IX are in pipeline).