Participação de canais iônicos na transdução do sinal osmótico em astrócitos hipotalâmicos em cultura

Abstract

Recent evidence shows that astrocytes are essential elements to the adaptive responses induced by osmotic challenges. In neurons, the osmotic signal transduction is mediated by the opening or closing of ion channels, some of which are also expressed by astrocytes, such as transient potential receptor vanilloid type 1 (TRPV1), stretch-innativated channels (SIC) and L-type calcium channels (LTCCs). Thus, the present study aimed to evaluate cell viability, astrocyte morphology (through the expression of the Glial Fibrillary Acidic Protein - GFAP) and the uptake of tritiated aspartate in the presence of hyperosmolality and selective ion channel blockers. The cells were incubated under basal conditions (DMEM Base: ~ 300 mOsm / kg H2O, 109 mM NaCl) and under conditions of increased extracellular sodium concentrations (Hypertonic DMEM: ~ 360 mOsm / kg H2O, 132 mM NaCl) in the presence of specific ion channel blockers (Verapamil, 10 μM, LTCC blocker; Capsazepine, 30 μM, TRPV1 antagonist; Gadolinium, 100 μM, SIC blocker). Interestingly, only Capsazepine showed a significant effect on cellular viability, decreasing astrocytes death rate. Incubation with hypertonic DMEM significantly reduced GFAP expression in hypothalamic astrocytes, as well as the uptake of tritiated aspartate. A similar effect of reduced GFAP expression was observed under basal conditions in response to incubation with Verapamil. However, incubation with Verapamil did not alter aspartate uptake, either under basal or hypertonic conditions. Incubation with Capsazepine, in turn, reversed the response induced by hypertonic DMEM on GFAP expression, without interfering with aspartate uptake. And, finally, blocking the SIC channels by incubation with Gadolinium, induced an aberrant response of increased GFAP expression, only in the presence of the hypertonic medium. Thus, we have concluded that LTCCs play an important role in GFAP expression, preferably under basal conditions or those unrelated to osmotic stimulation. On the other hand, TRPV1 channels, and especially SIC, seem to play fundamental roles in the structural rearrangements observed in astrocytes in response to the hypertonic stimulus. LTCCs and TRPV1, in turn, do not appear to mediate changes in glutamate transport in the presence of hypertonicity. The SICs have shown to increase such transport.