Ma. Lal et al., A ROLE FOR PKC-EPSILON AND MAP KINASE IN BRADYKININ-INDUCED ARACHIDONIC-ACID RELEASE IN RABBIT CCD CELLS, American journal of physiology. Renal, fluid and electrolyte physiology, 43(4), 1998, pp. 728-735
Arachidonic acid (AA) release is the rate-limiting step in the product
ion of prostaglandins, an important class of autocrine/paracrine facto
rs that modulate collecting duct function. Previous results from this
laboratory have established cytosolic phospholipase A(2) (cPLA(2)) as
the enzyme responsible for bradykinin (BK)-stimulated AA mobilization
in rabbit cortical collecting duct (RCCD) cells, and the present study
pursues the intracellular signaling mechanisms responsible for its ac
tivation. Pretreatment of cells with Ro-31-8220, an inhibitor of prote
in kinase C (PKC), or PD-98059, an inhibitor of the mitogen-activated
protein kinase (MAPK) cascade, resulted in a 50-60% reduction in BK-st
imulated AA release. Incubation of RCCD cells with a combination of bo
th Ro-31-8220 and PD-98059 did not achieve a greater inhibition of eit
her BK-stimulated AA release or cPLA(2) activity, possibly indicating
that MAPK activation was dependent upon prior activation of PKC. This
was supported by the observation that BK-induced MAPK activation could
be reversed by either inhibitor Additional experiments dealing with i
mmunoblots for PKC isozymes revealed that RCCD cells express PKC speci
es alpha, gamma, epsilon, and zeta. Following BK stimulation, only PKC
epsilon translocated to the particulate fraction. Based on these resu
lts, it appears that PKC is activated and involved in the sequential a
ctivation of MAPK and cPLA(2) following BK treatment. The results also
suggest that PKC epsilon may be the isozyme implicated in the process
.