Biophysical Journal 58: 253-259 (1990)
© 1990 the Biophysical Society

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A stimulus-activated conductance in isolated taste epithelial membranes.

Monell Chemical Senses Center, Philadelphia, Pennsylvania 19104.

ABSTRACT

Membrane vesicles isolated from the cutaneous taste epithelium of the catfish were incorporated into phospholipid bilayers on the tips of patch pipettes. Voltage-dependent conductances were observed in approximately 50% of the bilayers and single-channel currents having conductances from 8 to greater than 250 pS were recorded. In 40% of the bilayers displaying no voltage-dependent conductances, micromolar concentrations of L-arginine, a potent stimulus for one class of catfish amino acid taste receptors, activated a nonselective cation conductance. The L-arginine-gated conductance was concentration-dependent, showing half-maximal activation in response to approximately 15 microM L-arginine. L-Arginine-activated channels had unitary conductances of 40-50 pS and reversed between -6 and +18 mV with pseudointracellular solution in the pipette and Ringer in the bath. L-Alanine, a potent stimulus for the other major class of catfish amino acid taste receptors, did not alter bilayer conductance. D-Arginine, which is a relatively ineffective taste stimulus for catfish but a good cross-adapter of the L-arginine-induced neural response, had no effect on bilayer conductance at concentrations below 200 microM. However, increasing concentrations of D-arginine from 1 to 100 microM progressively suppressed the L-arginine-activated conductance, suggesting that D-arginine competed for the L-arginine receptor, but did not activate the associated cation channel. This interpretation is consonant with recent biochemical binding studies in this system. These results suggest that L-arginine taste receptor proteins in the catfish are part of or closely coupled to cation-selective channels which are opened by L-arginine binding.