COMPLEX SHAPE CHANGES IN ISOLATED RAT OSTEOCLASTS - INVOLVEMENT OF PROTEIN-KINASE-C IN THE RESPONSE TO CALCITONIN

The cytoplasmic spreading of osteoclasts has been used to assess respo nsiveness to agents such as calcitonin and associated signal transduct ion mechanisms. Although cyclic AMP and intracellular calcium are know n mediators of calcitonin effects in osteoclasts, the role of protein kinase C (PKC) is less clear. We have used time-lapse videomicroscopy of isolated rat osteoclasts to characterize shape changes induced by c alcitonin, forskolin, and phorbol 12-myristate-13-acetate (PMA) in the absence and presence of PKC blockers. Treatment with calcitonin reduc ed cytoplasmic plan area but increased perimeter length, resulting in a characteristic ''stellate'' appearance, whereas forskolin produced ' 'nonstellate'' contraction. The response of osteoclasts to PMA was dos e dependent. High concentrations (10(-7)-10(-6) M) produced biphasic r esponses with transitory, calcitonin-like ''stellate'' contraction fol lowed by sustained expansion, whereas low concentrations (10(-11) - 10 (-9) M) produced expansion only. The effects of low-concentration PMA could be prevented by pretreatment with a PKC blocker, whereas the eff ects of high concentrations were only partially inhibited. The effects of forskolin were unchanged by pretreatment with the PKC blocker. Tre atment with calcitonin in the presence of various PKC blockers resulte d in paradoxical transient expansion followed by contraction. These re sults indicate that calcitonin-induced shape change in osteoclasts is a complex process involving protein kinase C in addition to cyclic AMP -dependent mechanisms and possibly other factors.