CA-2+ TRANSPORT AND CHEMORECEPTION IN PARAMECIUM

Intracellular Ca2+ levels in Paramecium must be tightly controlled, ye t little is understood about the mechanisms of control. We describe he re indirect evidence that a phosphoenzyme intermediate is the calmodul in-regulated plasma membrane Ca2+ pump and that a Ca2+-ATPase activity in pellicles (the complex of cell body surface membranes) is the enzy me correlate of the plasma membrane pump protein. A change in Ca2+ pum p activity has been implicated in the chemoresponse of paramecia to so me attractant stimuli. Indirect support for this is demonstrated using mutants with different modifications of calmodulin to correlate defec ts in chemoresponse with altered Ca2+ homeostasis and pump activity.