Answer
Paracrines act on neighboring cells. on the other hand autocrine act on the same cells that secreted them. Histamine, secreted by mast cells, act on H2 receptors of parietal cells which then secrete protein kinase which converts ATP to cAMP. Since histamine acts on neighboring cell type and not on the cell type that produced it, the histamine produced by the mast cells in these circumstances is a paracrine.
Work Step by Step
Histamine activates adenyl cyclase which acts on ATP to produce protein kinase . Protein kinase causes phosphorylation of surface proteins which activate the H+/K+ ATPase facilitated transport from cytoplasm to membranes .
