Effect of phosphodiesterase inhibitors on bradykinin-mediated prostaglandin E2 and cyclic AMP synthesis in renal papillary collecting tubule cells

Regulation of potassium conductance by prostaglandins in cultured renal epitheloid (Madin-Darby canine kidney) cells

Madin-Darby canine kidney (MDCK) cells form arachidonic acid metabolites following stimulation of several hormones known to modify the ion conductances at the plasma membrane. The present study has been performed to elucidate the influence of arachidonic acid on the electrical properties of subconfluent MDCK cells. As a result, arachidonic acid (1 or 10 mumol/l) leads to a transient hyperpolarization of the cell membrane, followed by a transient depolarization and a second, sustained hyperpolarization. The effects are inhibited by cycloxygenase inhibitor indomethacin (1 mumol/l). The initial transient hyperpolarization is mimicked by prostaglandin E2 (PGE2, 0.1 mumol/l), the sustained hyperpolarization by both PGE2 (0.1 mumol/l) and PGF2 alpha (0.1 mumol/l). The transient hyperpolarization is paralleled by an increase of potassium selectivity and a decrease of cell membrane resistance and is thus the result of increased potassium conductance. The transient depolarization is paralleled by an increase of chloride selectivity, reflecting an increase of chloride conductance. The sustained hyperpolarization is paralleled by an increase of cell membrane resistance, and increase of potassium selectivity and a decrease of chloride selectivity, and is thus the result of decreasing chloride conductance. The observations reveal a role of prostaglandins in the regulation of ion conductances in MDCK cells, which could well participate in the transport regulation by hormones.

Coordinate interactions of cyclic nucleotide and phospholipid metabolizing pathways in calcium-dependent cellular processes

It is hoped that his review enables the reader to appreciate the complexities implicit in the interactions among Ca2+, cyclic nucleotides, and phospholipid-metabolizing pathways in cell signal transduction. The interactions are varied and intricate, often involving several levels of cell amplification mechanisms. Upsetting the balance of fatty acids in membrane phospholipids can have detrimental effects on adenylate cyclase. Thus, n - 3 fatty acid enrichment of phospholipids suppresses adenylate cyclase activity. The effects of significant alterations in dietary fatty acids, such as might occur with the current vogue for n - 3 eicosapentaenoic acid and docosahexaenoic acid (fish oil) dietary enrichment regimens, will need to be assessed more fully with regard to stimulus-induced changes in cyclic nucleotide production in various tissues. Since the n - 3 fatty acids have not been demonstrated to affect guanylate cyclase activity, dietary changes in certain of these fatty acids would not be expected to contribute to changes in cGMP generation as much as in cAMP production. Moreover, the ingestion of large quantities of these n - 3 fatty acids can alter the profile of cyclooxygenase and lipoxygenase products produced in cells. According to the paradigm developed in this article, changes in the metabolism of fatty acids are amplified by alterations in cyclic nucleotide production and phospholipase activities, with the eventual physiological impact predicated on the tissue type and the specific stimulus response. There appears to be a rather clear distinction between the regulatory properties of eicosanoids regarding adenylate and guanylate cyclase activities. Whereas prostaglandins often stimulate adenylate cyclase activity, they have little effect on guanylate cyclase activity. On the other hand, the HETE compounds seem to play an important role in guanylate cyclase regulation in certain cells. Moreover, arachidonic acid affects adenylate cyclase activity without prior peroxidation, whereas endoperoxides and hydroperoxides are more effective than arachidonic acid with regard to guanylate cyclase stimulation. However, in the intact cell there is a strong implication that the dual stimulation of guanylate cyclase by Ca2+ and fatty acid evokes optimal enzyme activity. An advantage of multidimensional response mechanisms in cells includes the ability to recognize different stimuli and to respond with specific, coordinated responses modulated in their intensity and/or duration by messenger interaction. Few cell types respond to receptor stimulation in an all-or-none fashion, and the "milieu interior" depends on specific, graded responses to the autonomic nervous system and endocrine stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)