INTERFERENCE OF A SHORT-CHAIN PHOSPHOLIPID WITH ION-TRANSPORT PATHWAYS IN FROG-SKIN

The effects of mucosal application of the short-chain phospholipid did ecanoyl-L-alpha-phosphatidylcholine (DDPC: with two saturated 10-carbo n acyl chains) on active Na+ transport and transepithelial conductance (G) in the frog skin (Rana temporaria) were investigated. Active Natransport was measured as the amiloride-sensitive short-circuit curren t (I-SC) and G was determined from transepithelial voltage-clamp pulse s under short-circuit conditions. DDPC dose-dependently inhibited I-SC , with an ID50 of about 0.05% (w/v) and a maximal effect (approximate to 55%) at greater than or equal to 1% DDPC. G increased to steady-sta te values above control level. Simultaneously, equal increases in unid irectional sucrose permeabilities (P-Su; measured from [C-14]sucrose f luxes) were observed, and a positive correlation was demonstrated betw een DDPC-induced changes in P-Su and G. Since amiloride did not preven t the increase in G by DDPC, these results suggest that the DDPC-induc ed increase in G represents an increase in the paracellular shunt cond uctance. The effects of mucosal DDPC were almost fully reversible with in 8 h. The results indicate that DDPC inhibits amiloride-sensitive Na + channels in the apical membrane of the frog skin epithelium and open s a paracellular tight junction pathway. Both effects may be caused by incorporation of DDPC in the apical cell membrane.