Ion channel gating in plants: Physiological implications and integration for stomatal function

Blatt, Michael R.

doi:10.1007/bf01870455

Cited by 102 publications

(81 citation statements)

References 172 publications

(278 reference statements)

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“…Noteworthy, the same voltage sensitivity (z = 2) has been determined not only for the KD channel in the intact cell (Blatt, 1991), but also for the classical delayed rectifier channel in the squid giant axon (Spires and Begenisich, 1992).…”

Section: Discussionmentioning

confidence: 75%

“…4, we estimated E0 to be + 11 mV, and from those of Fairley-Grenot and Assmann, + 16 mV (1992; we estimated this shift based on the maximum and half-maximum chord conductances extracted from their published averaged data). Interestingly, in the intact cells (Blatt, 1988(Blatt, , 1990(Blatt, , 1991(Blatt, , 1992; E0's estimated as before) the values of E0 appear to vary between preparations, even with similar external solutions, between ~-10 and ~-50 mV. While in the intact cells, E0 shift might reflect the shift in EK (Moran, Iwasa, Ehrenstein, Mischke, Bare, and Satter, 1987; also see Blatt, 1991), the internal [K +] would have to vary roughly fivefold to account for the observed range of E0, of ~ 40 InV.…”

Section: Discussionmentioning

confidence: 99%

“…Interestingly, in the intact cells (Blatt, 1988(Blatt, , 1990(Blatt, , 1991(Blatt, , 1992; E0's estimated as before) the values of E0 appear to vary between preparations, even with similar external solutions, between ~-10 and ~-50 mV. While in the intact cells, E0 shift might reflect the shift in EK (Moran, Iwasa, Ehrenstein, Mischke, Bare, and Satter, 1987; also see Blatt, 1991), the internal [K +] would have to vary roughly fivefold to account for the observed range of E0, of ~ 40 InV. We tend to assume that the intact guard cells used in these experiments were rather uniform in their turgor, therefore--also in their K + content.…”

Section: Discussionmentioning

confidence: 99%

“…KH and KD channels are the most predominant K channel types in the plasma membrane of protoplasts from stomatal guard cells of Vicia faba (Hedrich and Schroeder, 1989), and, in fact, in most higher plant cells examined so far (Moran, Ehrenstein, Iwasa, Bare, and Mischke, 1986;Moran, Ehrenstein, Iwasa, Mischke, and Satter, 1988;Moran and Satter, 1989;Schauf and Wilson, 1987;Ketchum, Shrier, and Poole, 1989; see recent reviews by Tester, 1990;Blatt, 1991). The characterization of these channels in plants still lags behind their counterparts in animal cell membranes (see, for example, recent reviews by Sanders, 1990, Hille, 1992 in biophysical as well as in biochemical detail.…”

Section: Introductionmentioning

confidence: 99%

“…For example, we are not aware of any information on the density of negative surface charges near the ion channels in plant cell membranes. There are only very few attempts at modeling of channel gating in plants (Bertl, Klieber, and Gradmann, 1988;Sanders, 1990;Schroeder, 1989;Blatt, 1991Blatt, , 1992Van Duijn, 1993). When available, gating parameter estimates can serve as a reference for quantitative comparison with data from other systems.…”

Section: Introductionmentioning

confidence: 99%

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External pH effects on the depolarization-activated K channels in guard cell protoplasts of Vicia faba.

Ilan

Schwartz

Moran

1994

The Journal of General Physiology

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Previous studies reveal that the pH of the apoplastic solution in the guard cell walls may vary between 7.2 and 5.1 in closed and open stomata, respectively. During these aperture and pH changes, massive K § fluxes cross the cellular plasma membrane driving the osmotic turgor and volume changes of guard cells. Therefore, we examined the effect of extracellular pH on the depolarizationactivated K channels (KD channels), which constitute the K § efflux pathway, in the plasma membrane of Viciafaba guard cell protuplasts. We used patch clamp, both in whole cells as well as in excised outside-out membrane patches.Approximately 500 KD channels, at least, could be activated by depolarization in one protoplast (density: ~0.6 ~m-2). Acidification from pH 8.1 to 4.4 decreased markedly the whole-cell conductance, GK, of the KD channels, shifted its voltage dependence, GK-EM, to the right on the voltage axis, slowed the rate of activation and increased the ,rate of deactivation, whereas the single channel conductance was not affected significantly. Based on the GK-EM shifts, the estimated average negative surface charge spacing near the KD channel is 39 /~. To quantify the effects of protons on the rates of transitions between the hypothesized conformational states of the channels, we fitted the experimental macroscopic steady state conductancevoltage relationship and the voltage dependence of time constants of activation and deactivation, simultaneously, with a sequential three-state model CCO. In terms of this model, protonation affects the voltage-dependent properties via a decrease in localized, rather than homogeneous, surface charge sensed by the gating moieties. In terms of either the CO or CCO model, the protonation of a site with a pKa of 4.8 decreases the voltage-independent number of channels, N, that are available for activation by depolarization.

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Section: Discussionmentioning

confidence: 75%