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The effects of phorbol esters, epidermal growth factor (EGF) and angiotensin (ANG) II on the translocation of the alpha, delta and epsilon isozymes of protein kinase C in rat liver epithelial cells were investigated through Western blot analysis following subcellular fractionation of treated tissues. Phorbol esters induced the highest degree of membrane translocation of the different isozymes. Although the magnitude of translocation induced by both EGF and ANG II is low, the significant translocation of the delta and epsilon isozymes is enough to explain spatially defined effects.

The relationship between the extracellular signal-regulated protein kinase (ERK) and Ca2+ pool in rat liver epithelial cells was investigated. Results showed that ERK activity is increased by Ca2+ pool depletion induced by two independent methods. The first method involved the Ca2+ pool depletion by thapsigarin, while the second involved the addition of extracellular EGTA. Moreover, the increase in ERK activity by Ca2+ pool depletion was via the tyrosine kinase pathway.