Intracellular pH and chemoresponse to NH4+ in Paramecium.

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 NH4Cl, but appears to decline within 10 minutes, both in wild type cells and in two mutants which do not show sustained attraction to NH4Cl using the standard behavioral assay, the T-maze. We also present quantitative values of swimming parameters that underlie the response to NH4Cl.