afimoxifene and 5-nitro-2-(3-phenylpropylamino)benzoic-acid

Cell-attached channel recordings were made of an inward channel current in isolated rat pancreatic beta-cells incubated in the presence of diazoxide to clamp the membrane potential close to the K(+) equilibrium potential. With 42 mM Cl(-) in the pipette solution, a channel of approximately 200 pS was observed in 20-40% of patches which conducted an inward current at a pipette potential of 0 mV. The channel was activated by a rise in glucose concentration over the range 5-20 mM. The channel was also activated by methylglyoxal, possibly due to its metabolism to D-lactate, but not by the non-metabolizable glucose analogue 3- O-methyl glucose. The channel was activated by hypotonic cell swelling and was sensitive to inhibition by the anion channel blockers 4,4'-dithiocyanatostilbene-2,2'-disulphonic acid, 5-nitro-2-(3-phenylpropylamino) benzoic acid and 4-hydroxytamoxifen. Current reversal occurred at a pipette potential of approximately -67 mV. Raising [Cl(-)] in the pipette solution to 142 mM shifted the reversal potential to -52 mV. It is suggested that the channel is the volume-sensitive anion channel previously described in insulin-secreting cells. Activation of the channel by glucose could be important in generating a depolarizing current leading to increased electrical activity and insulin release, particularly at higher concentrations of glucose where K(ATP) channel activity is minimal.

Topics: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Animals; Anions; Estrogen Antagonists; Female; Glucose; Ion Channels; Islets of Langerhans; Male; Nitrobenzoates; Rats; Tamoxifen

Previous studies in enterocytes isolated from the villus region of small intestinal epithelium have identified a macroscopic current carried by Cl-. In this work a single-channel patch-clamp study was carried out in the same cells, and a spontaneously active, outwardly rectifying Cl- channel was identified and proposed to underlie the whole cell current. The channel had conductances of 62 and 19 pS at 80 and -80 mV, respectively, in symmetrical Cl- solutions in excised patches. Similar activity was seen in cell-attached patches, but only outward currents could be discerned in this configuration. The activity of the channel, measured as open probability, was independent of intracellular calcium levels and voltage. The selectivity sequence for different anions was SCN- > I- > Br- > Cl- > F- > (gluconate, glutamate, SO4(2-)). The channel was inhibited by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), verapamil, and 4-hydroxytamoxifen (but not by tamoxifen), with potencies similar to those observed for Cl- channels previously described in other cells. Inhibition by trinitrophenyladenosine 5'-triphosphate was also observed but only at depolarized potentials. At 50 mV the half-maximal inhibitory concentration was 18 nM. It is proposed that this channel plays a role in transepithelial Cl- transport and certain regulatory Cl- fluxes.

Topics: Adenosine Triphosphate; Animals; Anions; Cell Membrane; Cell Membrane Permeability; Chloride Channels; Glutamic Acid; Guinea Pigs; In Vitro Techniques; Intestinal Mucosa; Intestine, Small; Male; Membrane Potentials; Nitrobenzoates; Patch-Clamp Techniques; Tamoxifen; Verapamil