COLD-SENSITIVE CA2+ INFLUX IN PARAMECIUM

The concentration of intracellular calcium, [Ca2+](i), in Paramecium w as imaged during cold-sensitive response by monitoring fluorescence of two calcium-sensitive dyes, Fluo-3 and Fura-Red. Cooling of a decilia ted Paramecium caused a transient increase in [Ca2+](i) at the anterio r region of the cell. Increase in [Ca2+](i) was not observed at any re gion in Ca2+-free solution. Under the electrophysiological recording, a transient depolarization of the cell was observed in response to coo ling. On the voltage-clamped cell, cooling induced a transient inward current under conditions where K+ currents were suppressed. These memb rane depolarizations and inward currents in response to cooling were l ost upon removing extracellular Ca2+, The cold-induced inward current was lost upon replacing extracellular Ca2+ with equimolar concentratio n of Co2+, Mg2+ or Mn2+, but it was not affected significantly by repl acing with equimolar concentration of Ba2+ or Sr2+, These results indi cate that Paramecium cells have Ca2+ channels that are permeable to Ca 2+, Ba2+ and Sr2+ in the anterior soma membrane and the channels are o pened by cooling.