HCO 3 (-) and OH (-)transport across the plasmalemma ofChara : Spatial resolution obtained using extracellular vibrating probe.

Internodal and whorl (branch) cells of the green alga,Chara corallina Klein ex Willd., em. R.D.W., were studied with the extracellular vibrating probe for measuring transmembrane ion currents, and with an extracellular pH microprobe for measuring the surface pH profile. Bands of positive inward current (OH(-) efflux) 1-3 mm wide were separated by wider bands of outward current (HCO 3 (-) influx) along the length of the cell. The measured peaks of inward current ranged from 20 to 60 μA cm(-2) (98 μm from the cell surface) which would correspond to a surface ionic flux of 270-800 pmol cm(-2) s(-1). The peaks of outward current (HCO 3 (-) influx) ranged from 10 to 30 μA cm(-2) which would correspond to a surface ionic flux of 140-400 pmol cm(-2) s(-1). The inward current bands matched the regions of surface alkalinity very well. The outward current (HCO 3 (-) influx) was reduced at least 10-fold in low-HCO 3 (-) medium, with a commensurate readjustment in the strength and pattern of inward current (OH(-) efflux). (Although these experiments involved a manipulation of the external pH, it is felt that the main adjustment in current patterns was in response to the reduction in exogenous HCO 3 (-) ). The presence of the vibrating probe perturbed the inward current region when vibrating with a 26-μm amplitude, but this perturbation was eliminated when a 7-μm amplitude was used. The perturbation was usually observed as a reduction in the number of inward current peaks with an increase (approximate doubling) in the amplitudes of the one or two remaining peaks. Both the inward and outward currents were light-dependent, falling off within seconds of light removal.