ACTIVATION OF NONSELECTIVE CATION CHANNELS IN THE BASOLATERAL MEMBRANE OF RAT DISTAL COLON CRYPT CELLS BY PROSTAGLANDIN-E2

Ion channels in the basolateral membrane of colonic crypts were investigated with the patch-clamp technique during stimulation of secretion. Intact crypts were isolated from rat distal colon and the cell potential was recorded by addition of nystatin to the pipette solution. The cell resting potential in the base of the crypt was -74 +/- 1 mV (n = 90). Addition of 100-mu-M carbachol to the bath resulted in a transient hyperpolarization by 9 mV, which was probably due to the opening of basolateral K+ channels. In contrast, application of prostaglandin E2 (PGE2, 1-nM-1-mu-M) caused a dose-dependent depolarization in the base of the crypt. With 1-mu-M PGE2 cells depolarized from -74 +/- 1 to -27 +/- 2 mV (n = 26). Cell potential recordings in the midcrypt showed only a slight and transient depolarization after application of PGE2, whereas cells close to the surface of the crypt had no response. In the base of the crypt the PGE2-induced depolarization could be completely inhibited by addition of 50-mu-M flufenamic acid, a known blocker of nonselective cation channels. After substitution of all monovalent cations by N-methyl-D-glucamine in the bath, PGE2 had no significant effect on the cell potential. Cell-attached experiments with no nystatin in the patch pipette revealed the activation of ion channels in the basolateral membrane after application of PGE2. After excision of the membrane patch, these channels could be identified as nonselective cation channels. Experiments involving substitution of the bath solution showed that the channel is impermeable for Cl-and scarcely permeable for Ca2+ ions. The permeability sequence for monovalent cations, as calculated from reversal potentials, is NH4+ > Na+ = K+ > Rb+ = Li+ >> TRIS+ = NMDG+. Single channels are completely inhibited by flufenamic acid (50-mu-M), mefenamic acid (200-mu-M), as well as by 3', 5-dichlorodiphenylamine-2-carboxylate. In conclusion, PGE2 activates nonselective cation channels in the basolateral membrane of cells in the base of colonic crypts. It is suggested that this mechanism initiates the secretion of K+ ions. Na+ influx through the nonselective cation channel will stimulate the Na+/K+ pump and active uptake of K+ at the basolateral side. K+ can leave the cell at the luminal side through K+-selective channels.