H+ Fluxes in Excised Samanea Motor Tissue

Abstract

Previous investigators revealed that white light-promoted leaflet opening in S. saman (Jacq) Merrill depends upon K+ uptake by extensor cells and efflux from flexor cells of the pulvinus, while dark-promoted closure depends upon K+ fluxes in the opposite directions. H+ fluxes were monitored during pulvinar movement to test a model proposing coupled H+/K+ fluxes. H+ fluxes were monitored by measuring changes in the pH of a weakly buffered solution (initial pH = 5.5) bathing excised strips of extensor or flexor tissue. White light at hour 3 of the usual dark period promoted pulvinar opening, H+ efflux from extensor cells and uptake by flexor cells, while darkness at hours 2-4 of the usual light period promoted pulvinar closure, H+ uptake by extensor cells and efflux from flexor cells. The following conditions altered H+ fluxes during dark-promoted closure. Light reversed the directions of the fluxes in both extensor and flexor cells. Anoxia increased the rate of H+ uptake by extensor cells and promoted H+ uptake (rather than efflux) by flexor cells, consistent with an outwardly directed H+ pump. KCN showed similar effects initially, but they were transient. Increase in external pH from 5.5 to 6.7 promoted H+ efflux (rather than uptake) by extensor cells and increased the rate of H+ efflux from flexor cells, presumably by decreasing the rate of inward diffusion. Change in external K+ did not alter H+ fluxes by extensor cells, but removal of external K+ decreased the rate of H+ effux from flexor cells by 70%. These observations support a model for coupled H+/K+ fluxes in pulvinar cells during light-and dark-promoted leaflet movements.