Effects of parathyroid hormone in vivo on the protein kinase activity in rat kidney

Abstract

Parathyroid hormone (PTH) was infused into thyroparathyroidectomized rats, and the protein kinase activity of the kidney was studied. When the tissue was homogenized in a buffer containing 5 mM potassium phosphate (pH 7.0), 2 mM EDTA, 1 mM mercaptoethanol, and 5 mM theophylline, the total protein kinase activity (measured in the presence of 5 muM cAMP) in the cytosol was decreased by the infusion of PTH, exhibiting an inverse relationship to cAMP level in the renal tissue. The decrease of total activity was accounted for by a decrease of cAMP-dependent kinase activity, and such a change was induced also by the infusion of calcitonin or dibutyryl cAMP. A substantial enzyme activity was solubilized from the particulate fraction with a buffer containing KC1. The infusion of PTH increased the kinase activity (activities measured in both the presence and absence of cAMP) solubilized from the particulate fraction, suggesting the translocation of activated enzyme from cytosol to some particulate cell component(s). However, when KC1 was added to the homogenization buffer in concentrations up to 150 mM or even higher, the total protein kianse activities in the cytosols of control and PTH rats were similar and there was simply an increase in the fraction of cAMP -independent activity. These observations indicate that the hormonally-induced increase of cAMP in vivo activates protein kinase of the kidney, and the activation of kinase results in apparent translocation of the enzyme from the soluble to the particulate fraction when the tissue is homogenized in buffers of low ionic strength. The physiological significance of this phenomenon, however, cannot be evaluated, due to the fact that the increased association of activated kinase with particulate component(s) is reversed by employing a homogenization buffer containing what is probably a physiological concentration of salt.