The significance of apical K+ channels in mudpuppy feeding behavior

Behavioral experiments were conducted to determine the effects of known potassium channel blockers, minnow extract (a natural food substance), and other taste stimuli on feeding behavior in the mudpuppy (Necturus maculosus). Groups of 10-15 mudpuppies were presented with one or more of the following chemicals dissolved in gelatin cubes: H2O (control), NaCl (1.0 M; 0.2 M), crude minnow extract (0.1 g/ml), CaCl2 (1.0 M), citric acid (0.1 M; pH 2, 0.01 M; pH 3), quinine HCl (0.1 M), tetraethylammonium chloride (TEA; 0.1 M), KCl (1.0 M) and an amino acid mixture containing L-phenylalanine, L-arginine, L-histidine, L-valine, L-glutamic acid and L-lysine at concentrations of 0.02 M and 0.04 M each. Crude minnow extract was centrifuged and separated into components consisting of the following fractions: > 500 D, > 1000 D and > 14,000 D, each of which was presented to mudpuppies in cubes. Results were expressed as the percentage of animals rejecting the cube within 5 min of taking the cube into the oral cavity. Statistical analysis using the Fisher exact test indicated that cubes containing chemicals known to block (CaCl2, TEA, citric acid and quinine) or permeate (KCl) apical K+ channels in mudpuppy taste cells were more aversive than control cubes, and aversion was concentration-dependent. In contrast, cubes containing minnow extract and components of minnow extract < 14,000 D were significantly preferred over control cubes. Cubes containing a mixture of minnow extract and an aversive chemical were significantly less aversive than cubes containing only an aversive chemical. These findings suggest that activation of the apical K+ conductance in mudpuppy taste cells triggers an aversive response, but the aversion can be ameliorated by low molecular weight compounds present in minnow extract.