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Membrane phosphatidylinositol- 4,5-bisphosphate (PIP2) is critical for the function of many transient receptor potential (TRP) ion channels. The role of PIP2 in TRPA1 function is not well known. The effect of PIP2 on TRPA1 was investigated by direct application of PIP2 and by using polylysine and PIP2 antibody that sequester PIP2. In inside-out patches from HeLa cells expressing mouse TRPA1, polytriphosphate (PPPi) was added to the bath solution to keep TRPA1 sensitive to allyl isothiocyanate (AITC; mustard oil). Direct application of PIP2 (10 µM) to inside-out patches did not activate TRPA1, but AITC and Δ9-tetrahydrocannabinol (THC) produced strong activation. In inside-out patches in which TRPA1 was first activated with AITC (in the presence of PPPi), further addition of PIP2 produced a concentration-dependent inhibition of TRPA1 [agonist concentration producing half-maximal activity (K1/2), 2.8 µM]. Consistent with the inhibition of TRPA1 by PIP2, AITC activated a large whole cell current when polylysine or PIP2 antibody was added to the pipette but a markedly diminished current when PIP2 was added to the pipette. In inside-out patches with PPPi in the bath solution, application of PIP2 antibody or polylysine caused activation of TRPA1, and this was blocked by PIP2. However, TRPA1 was not activated by polylysine and PIP2 antibody under whole cell conditions, suggesting a more complex regulation of TRPA1 by PIP2 in intact cells. These results show that PIP2 inhibits TRPA1 and reduces the sensitivity of TRPA1 to AITC. [ABSTRACT FROM AUTHOR]

Examines adenosine triphosphate (ATP)-dependent regulation of a G protein-coupled potassium channel expressed in oocytes. Effect of the antagonistic regulation of G protein-gated potassium channels by ATP; Reversal of effects to ATP by cytosolic extract from atria; Inward rectification of potassium channels by polyamines.

Studies the properties of G protein-coupled potassium (K+) channels, GIRK1 and GIRK4, expressed in oocytes. Regulation of GIRK1 and GIRK4 with an ATP-dependent process inhibited by a cytosolic protein resulting in rapid desensitization; Formation of heteromultimer resembling muscarinic K+ channel; Activation of an inwardly rectifying K+ channel with acetylcholine.

Presents a study that examined how proteases, changes in intracellular pH, and different anions affect G protein-mediated activation and ATP-induced stimulation of KACh channel. Behavior of KACh with respect to G protein-induced activation; Methodology; Results of the study.