EFFECT OF TEMPERATURE ON APICAL MEMBRANE REMODELING IN ADH-STIMULATEDTOAD URINARY BLADDERS

Pretreatment and removal of vasopressin (ADH) in toad urinary bladder renal model tissues induces endocytosis at 25 degrees C, The objective of the current study is to determine if apical membrane remodeling, a s well as transepithelial water flow, can be affected by lowering the temperature to 15 degrees C, Control toad urinary bladders in the pres ence of an osmotic gradient at either 25 degrees C or 15 degrees C whe n visualized by scanning electron microscopy (SEM) show a typical apic al membrane surface with no apparent surface differences, ADH-treated tissues following 15-min stimulation at 25 degrees C or 15 degrees C r evealed a propagation of apical microvilli on their surface membranes. After 15 min following removal of ADH, bladder tissues at 25 degrees C or 15 degrees C showed surface invaginations involving over 44% and 80% of granular cells, respectively. The rate of water flow in tissues at 15 degrees C remained elevated compared to tissues held at 25 degr ees C. This was consistent with the observation that ADH-stimulated ti ssues following washout at 15 degrees C still had marked apical membra ne surface involvement. However, at 30 min and 60 min postwashout, ADH -stimulated tissues at 15 degrees C recovered considerably, with a red uction in the number of shallow apical membrane invaginations involvin g fewer than 33% and 20% of granular cells respectively. This may indi cate that the membrane undergoes continuous remodeling even at cold te mperature conditions but with a different half-time, Control bladder t issues subjected to transmission electron microscopy (TEM) reveal a de nse cytoplasmic profile with a scattered distribution of secretory gra nules, rough ER cisternae, mitochondria, and little or no vacuolation. In contrast, ADH-stimulated bladder tissues displayed a vacuolated cy toplasm, expanded rough ER cisternae, and ruffled basolateral membrane s. These observations suggest that the apical membrane undergoes consi derable reorganization following cessation of hormone action and that lowering the temperature reduces the rate of membrane remodeling and t hus may provide a means to monitor the processes of endocytosis and th e mechanisms responsible for water channel retrieval.