Taste receptors in crayfish: recording of single nicotinamide-activated channels.

The patch clamp technique was adapted to chemoreceptive sensory cells in the claw of Austropotamobius torrentium. In cell-attached and in outside-out patches, concentrations of nicotinamide from 10(-6) mol/liter to 5 X 10(-5) mol/liter activated openings of single channels located in the cell body of the sense cell. The characteristics of these single channel openings were similar to those of neurotransmitter activated channels: the I/V curve was approximately linear, showing a reversal potential of about +15 mV and a conductance of about 33 pS. The mean open time was 1-2 ms. A similar concentration dependence was found for the activation of single channel openings as shown previously for the action potential discharge elicited by nicotinamide at the same preparation.