Temporal expression of calcium/calmodulin-dependent adenylyl cyclase isoforms in rat articular chondrocytes: RT-PCR and immunohistochemical localization

A multitude of signalling cascades are implicated in the homeostasis of articular chondrocytes. However, the identity of these signalling pathways is not fully established. The 3, 5'-cyclic AMP-mediated signalling system is considered to be a prototype. Adenylyl cyclase (AC) is an effector enzyme responsible for the synthesis of cAMP. There are 10 mammalian AC isoforms and some of these are differentially regulated by calcium/calmodulin (Ca²⁺/CaM). Ca²⁺ is known to play an important role in the development and maintenance of skeletal tissues. Ca²⁺/CaM-dependent AC isoforms and their temporal expression in articular chondrocytes in rats were identified using RT-PCR and immunohistochemistry techniques. All Ca²⁺/CaM-dependent AC isoforms were expressed in chondrocytes from all age groups examined. Each isoform was differentially expressed in developing and adult articular chondrocytes. Generally, expression of AC isoforms was observed to increase with age, but the increase was not uniform for all Ca²⁺/CaM-dependent AC isoforms. Expression of Ca²⁺/CaM-dependent AC isoforms along with other signalling molecules known to be present in articular chondrocytes indicate complicated and multifactorial signalling cascades involved in the development and homeostasis of articular cartilage. The significance of these findings in terms of articular chondrocyte physiology is discussed.