Participação dos canais transient receptor potencial vanilloid type 1 (TRPV1) de astrócitos hipotalâmicos no controle central do balanço de água e sódio

Abstract

The Central Nervous System is composed of neurons and glial cells, with astrocytes being essential in neurotransmission. This study investigated the effects of variations in extracellular fluid osmolality (ECF) on astrocytic function parameters. Using an in vitro model of primary culture of astrocytes derived from the medio-basal hypothalamus of neonatal rats, cells were pre-incubated for 30 minutes with conventional culture medium, with or without Capsazepine. Subsequently, they were stimulated for 2 hours with Hank's solutions of different osmolalities (230, 290, or 350 mOsm/kg H2O). Cell viability and cell area were analyzed, with the latter estimated by quantifying the expression of glial fibrillary acidic protein (GFAP). In vitro lactate release, intracellular calcium (Ca2+) concentrations, and total protein quantification were determined through colorimetric reactions, performed with the incubation medium or with cell lysates obtained after 1 or 2 hours of stimulation. Results were evaluated by two-way ANOVA, with Sidak's post-test. Cell viability remained unchanged in the face of osmolality variations or Caps treatment. GFAP expression was reduced in the group incubated with Hank's solution of 230 mOsm/kg H2O, and Caps treatment reversed this response (p<0.05). Lactate release was not altered after exposure to changes in ECF osmolality. However, Caps incubation significantly increased lactate concentrations in the medium after 2 hours of stimulation (p<0.001), regardless of ECF osmolality. At the lower osmolality (230 mOsm/kg H2O), Caps treatment also increased lactate release after 1 hour of stimulation (p<0.01). No relevant changes were found in total intracellular Ca2+ concentrations in astrocytes incubated for 2 hours under different ECF osmolalities. Caps treatment, however, reduced this parameter only in the group incubated with Hank's solution of 290 mOsm/kg H2O (p<0.01). TRPV1 channel blockade affects GFAP expression and lactate release, especially under hypotonic conditions. However, Ca2+ balance is not significantly impacted by TRPV1 channel antagonism during osmotic challenges, except under isotonic conditions.