Intracellular pH and chemoresponse to NH4+ inParamecium

Abstract

Paramecium are attracted to ammonium chloride solutions relative to sodium chloride control solutions, but little is known about the mechanisms by which attraction is evoked. A known effect of ammonium solutions in other cell types is an alteration of intracellular pH. We show here that intracellular pH is elevated upon initial exposure to 5 mM NH 4 Cl, but appears to decline within 10 minutes, both in wild type cells and in two mutants which do not show sustained attraction to NH 4 Cl using the standard behavioral assay, the T-maze. We also present quantitative values of swimming parameters that underlie the response to NH 4 Cl.

Veratridine-Mediated Ca 2+ Dynamics and Exocytosis in Paramecium Cells

“…At pH 7.3, as used here for extracellular application, veratridine is lipophilic and thus can "see" targets in the cell membrane, while it also enters cells [8,22]. The cytosolic pH of Paramecium is unexpectedly low, i.e., 6.6, as recently reported [11]. Protonation fully activates veratridine [22] and, thus, can explain some of the effects we see in Paramecium, for instance internal trichocyst decondensation, as discussed below.…”

Genetic dissection of attractant-induced conductances inParamecium

“…Paramecia were pipetted in 2-3·l into a 50·l volume of test solution on a glass slide placed on a StereoZoom 7 dissecting microscope (Bausch and Lomb, Rochester, NY, USA). Cells were just off screen when put on the slide and videotaped using a video camera (Cohu 6410, San Diego, CA, USA) attached to a Sony SLV-R5UC video cassette recorder as they swam into view (~1·s) (Davis et al, 1998). Cell images were processed using a VP 110 video processor (Motion Analysis Corp.).…”

“…A number of bacterial metabolites are attractant stimuli, including glutamate, folate, biotin, cAMP, acetate and ammonium (Bell et al, 1998;Yang et al, 1997;Van Houten, 1994) and, except for ammonium, these stimuli bind to cell surface receptors to initiate the responses. In contrast, the attractant NH 4 Cl diffuses as ammonia across the cell membrane, which results in alkalinization, hyperpolarization and altered swimming behavior (Davis et al, 1998). The response of the cells to the application of any of the other stimuli is an immediate decrease in frequency of turning and an increase in swimming speed.…”

Effect of pH on growth, cell volume, and production of freshwater ciliates, and implications for their distribution

“…Further, pH has a strong impact on the solubility, bioavailability, and toxicity of ammonium/ ammonia, iron, aluminum, and some other heavy metals (Anderson 1988;Wetzel 2001). Physiological mechanisms and adaptations to withstand fluctuating pH have been studied in some protist species (e.g., Knitt and Herschlag 1996;Davis et al 1998). Irrespective of the specific cellular strategy for coping with changing pH, to maintain a stable pH gradient under fluctuating external hydrogen ion concentrations requires energy that is unavailable for anabolic processes.…”