Blue light modulation of ion transport in the slime mutant of Neurospora crassa.

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Blue light is the primary entrainment signal for a number of developmental and morphological processes in the lower eucaryote Neurospora crassa. Blue light regulates photoactivation of carotenoid synthesis, conidiation, phototropism of perithecia and circadian rhythms. Changes in the electrical properties of the plasma membrane are one of the fastest responses to blue light irradiation. To enable patch-clamp studies on light-induced ion channel activity, the wall-less slime mutant was used. Patch-clamp experiments were complemented by non-invasive ion-selective measurements of light-induced ion fluxes of slime cells using the vibrating probe technique. Blue light usually caused a decrease in conductance within 2-5 minutes at both negative and positive voltages, and a negative shift in the reversal potential in whole-cell patch-clamp measurements. Both K+ and Cl- channels contribute to the inward and outward currents, based on the effects of TEA (10 mM) and DIDS (500 microM). However, the negative shift in the reversal potential indicates that under blue light the Cl- conductance becomes dominant in the electrical properties of the slime cells due to a decrease of K+ conductance. The ion-selective probe revealed that blue light induced the following changes in the net ion fluxes within 5 minutes: 1) decrease in H+ influx; 2) increase in K+ efflux; and 3) increase in Cl- influx. Ca2+ flux was unchanged. Therefore, blue light regulates an ensemble of transport processes: H+, Cl-, and K+ transport.