CYTOSKELETAL REGULATION OF ION-CHANNEL DISTRIBUTION IN THE TIP-GROWING ORGANISM SAPROLEGNIA-FERAX

Growing hyphal tips of the oomycete Saprolegnia ferax possess a tip-hi gh gradient of stretch-activated ion channels permeable to calcium. Th ese mechanosensitive channels appear to play a direct role in the pola rized tip growth process. Treatment of S. ferax hyphae with cytochalas in E leads to the disruption of plasmalemma-associated, peripheral cyt oplasmic actin populations and altered morphology of apical protoplast s, and eliminates the tip-high gradient of stretch-activated channels. Cytochalasin E did not alter the normal aggregation of stretch-activa ted channels. The density of spontaneous K+ channels was decreased in all regions of the hyphae after treatment with cytochalasin E. These r esults suggest that the peripheral F-actin network in the growing tip of S. ferax hyphae establishes or maintains the tip-high gradient of S A channels, either by the delivery of channel-bearing vesicles to the apex or by the interactions between the channels and the peripheral ac tin network.