Garrill A, Jackson S L, Lew R R, Heath I B
Department of Biology, York University, Toronto/Canada.
Eur J Cell Biol. 1993 Apr;60(2):358-65.
The plasma membrane of tip-growing hyphae of the oomycete Saprolegnia ferax contains stretch-activated (SA) Ca(2+)-permeable and Ca(2+)-activated K+ ion channels. Patch clamp measurements on protoplasts derived from specific regions of hyphae demonstrated that SA channels were most abundant in the tip. Gadolinium (Gd3+) inhibited SA channel activity and stopped tip growth. The Ca(2+)-sensitive fluorochrome INDO 1 revealed a tip-high gradient of free cytoplasmic Ca2+ in growing hyphae. This gradient could be dissipated with the addition of Gd3+. The calcium gradient returned and growth resumed when Gd3+ was washed out. This implies a fundamental requirement for growth for Ca2+ influx through the SA channels. Ca(2+)-activated K+ channels were distributed evenly along the hyphae. These channels were inhibited by tetraethylammonium concentrations which caused a rapid but transient decrease in growth. We suggest that the SA channels at the apex act as feedback sensors, responding to membrane stretching at the tip. They are an obligate requirement for tip growth. The Ca(2+)-activated K+ channels may act to maintain turgor pressure, but are not obligatory for growth.
卵菌纲真菌水霉的顶端生长菌丝的质膜含有牵张激活（SA）的Ca（2+）通透性通道和Ca（2+）激活的K+离子通道。对来自菌丝特定区域的原生质体进行膜片钳测量表明，SA通道在顶端最为丰富。钆（Gd3+）抑制SA通道活性并阻止顶端生长。Ca（2+）敏感荧光染料INDO 1显示，生长菌丝中游离细胞质Ca2+呈顶端高梯度分布。加入Gd3+可消除这种梯度。当洗去Gd3+时，钙梯度恢复，生长重新开始。这意味着通过SA通道的Ca2+内流是生长的基本要求。Ca（2+）激活的K+通道沿菌丝均匀分布。这些通道被四乙铵浓度抑制，这会导致生长迅速但短暂下降。我们认为顶端的SA通道作为反馈传感器，对顶端的膜拉伸做出反应。它们是顶端生长的必要条件。Ca（2+）激活的K+通道可能起到维持膨压的作用，但不是生长所必需的。
