Proton currents through amiloride-sensitive Na channels in hamster taste cells. Role in acid transduction.

Abstract

A B S T R A C T The activity of taste cells maintained in the intact hamster tongue was monitored in response to acid stimulation by recording action currents from taste receptor cells with an extraceUular "macro" patch pipette: a glass pipette was pressed over the taste pore of fungiform papillae and perfused with citric acid, hydrochloric acid, or NaC1. Because this technique restricted stimulus application to the small surface area of the apical membranes of the taste cells, many nonspecific, and potentially detrimental, effects of acid stimulation could be avoided. Acid stimulation reliably elicited fast transient currents (action currents of average amplitude, 9 pA) which were consistently smaller than those elicited by NaCI (29 pA). The frequency of action currents elicited by acid stimuli increased in a dose-dependent manner with decreasing pH from a threshold of about pH 5.0. Acid-elicited responses were independent of K +, Na +, CI-, or Ca 2+ at physiological (salivary) concentrations, and were unaffected by anthracene-9-carboxylic acid, tetraethylammonium bromide, diisothiocyanate-stilbene-2,2'-disulfonic acid, vanadate, or Cd 2+. In contrast, amiloride (<30 I~M) fully and reversibly suppressed acid-evoked action currents. At submaximal amiloride concentrations, the frequency and amplitude of the action currents were reduced, indicating a reduction of the taste cell apical conductance concomitant with a decrease in cell excitation. Exposure to low pH elicited, in addition to transient currents, an amiloride-sensitive sustained d.c. current. This current is apparently carried by protons instead of Na + through amiloride-sensitive channels. When citric acid was applied while the taste bud was stimulated by NaCI, the action currents became smaller and the response resembled that produced by acid alone. Because of the strong interdependence of

A Role for Proton Signaling in the Induction of Somatic Cells to Pluripotent Embryonic Stem Cells

“…As was observed previously, s study of Xenopus oocytes showed a depolarization of the membrane potential by fertilization, which will induce Na + entry into the cell [20]. It was also found that the proton current can flow through (amiloridesensitive) Na + channels in the hamster taste cells [21]. Taken together, these findings lead us to speculate that a protocol of acidic stimulation (as Obokata et al did for reprogramming [1]) will induce Na + entry, which will induce an increase in intracellular proton level initially; then the water state will be changed gradually from the bound state to the free state, which will initiate a new cell cycle as described above.…”

Postnatal Development of Membrane Excitability in Taste Cells of the Mouse Vallate Papilla

“…Action potential firing appears to be one important step in the transduction and signaling of sensory information in taste buds. For example, the frequency of spike discharge is related to the concentration of certain stimuli (Gilbertson et al, 1992;Cummings et al, 1993). In addition, membrane depolarization during action potential seems to be necessary to activate Ca 2ϩ channels for neurotransmitter release underlying signal transfer to afferent nerves (Béhé et al, 1990;Furue and Yoshii, 1997).…”

“…Action potential discharges are regularly recorded from taste cells during chemostimulation in mammals (Béhé et al, 1990;Avenet and Lindemann, 1991;Gilbertson et al, 1992;Cummings et al, 1993;Furue and Yoshii, 1997;Ohtubo et al, 2001). Given the presence of voltage-gated Na ϩ currents, Na/OUT cells are able to fire action potentials (see below).…”

Acid-Sensitive Two-Pore Domain Potassium (K2P) Channels in Mouse Taste Buds

“…Taste cells express several proton-gated or proton-permeant cation channels that have been proposed to be sour taste transducers, including cation channels (ENaCs, MDEG1, ASIC-2b: Gilbertson and Gilbertson 1994;Gilbertson et al 1992;Liu and Simon 2001;Ugawa et al 1998), hyperpolarization-activated cyclic nucleotidegated channels (HCNs: Stevens et al 2001), and protonsensitive chloride channels (Miyamoto et al 2000). However, even though most of these ion channels are expressed in subsets of taste cells, it is not known whether these cells are the same cells that mediate acid taste.…”