CYCLICAL MORPHODYNAMICS OF HAIR BUNDLES IN SEA-ANEMONES - 2ND-MESSENGER PATHWAYS

Despite lacking sensory organs, sea anemones apparently integrate chemical and mechanical sensory input from prey in the regulation of nematocyst discharge. Exposing anemones to exogenous N-acetylated sugars induces hair bundles to elongate while shifting nematocyst discharge to lower frequencies matching swimming movements of prey. A pharmacological approach was employed to examine the transduction events involved in the sugar induced ''tuning'' of anemone hair bundles. Photoactivation of caged cyclic-AMP (cAMP) induces bundles to elongate to a maximum length by 4 min and subsequently to shorten to near control lengths by 8 min. Continuous stimulation with sugar produces a similar effect with the cycle continuing through at least 20 min. With sugar stimulation, nematocyst discharge into targets vibrating at 5 Hz also follows the same, cyclical pattern. Bundles do not elongate in the combined presence of N-acetylated sugars and H89, an inhibitor of protein kinase A. Elongated bundles either do not shorten, or rapidly recover from shortening, if caged cAMP is photoactivated 3.5 min after the initiation of sugar stimulation. Furthermore, bundle shortening is blocked by caffeine, an inhibitor of phosphodiesterase, W7, an inhibitor of calmodulin, nifedipine, an inhibitor of certain calcium channels, or cypermethrin, an inhibitor of protein phosphatase 2B (PP2B). Thus, chemodetection of sugars may involve an immediate elevation of intracellular cAMP, leading to an activation of protein kinase A, inducing bundles to elongate. Subsequently, calcium channels may be activated leading to a calcium/calmodulin dependent enhancement of phosphodiesterase and an activation of PP2B, inducing bundles to shorten by degrading cAMP and dephosphorylating proteins. (C) 1994 Wiley-Liss, Inc.