Light-induced changes of extra- and intracellular potassium concentration in photoreceptors of the leech,Hirudo medicinalis

Abstract

The potassium concentration was measured in the cytoplasm, perimicrovillar extracellular space (=‘vacuole’) and intercellular space of leech photoreceptors with double-barrelled potassium-sensitive microelectrodes in darkness and upon photostimulation. The mean intracellular potassium concentration in cells with membrane potentials >50 mV was 100±34 mmol/l. Photostimulation with 90 saturating 20 ms light flashes (1/s) evoked a potassium loss of 10.6±7.6 mmol/l. In the dark, there was no potassium concentration gradient between vacuole and intercellular space (K VAC + =4.5±0.9 mmol/l, K ECS + =4.5±0.5 mmol/l). In both compartments the potassium concentration increased upon repetitive photostimulation. Thus, the potassium loss from the cell is due to potassium movements across both the receptive and the non-receptive membrane domains.