Desensitization of intracellular calcium response to angiotensin II in dispersed adenohypophyseal cells

FEIERSTEIN C, GONZÁLEZ IGLESIAS A, SUÁREZ CECILIA, DÍAZ-TORGA G, BECÚ-VILLALOBOS D

Mar del Plata, Buenos Aires

Congreso; XXXI Reunión de la Sociedad Argentina de Farmacología Experimental; 1999

SAFE

We have characterized the phenomenon of desensitization of intracellular calcium response to angiotensin II (AII) in adenohypophyseal cells, using the fluorometric indicador Fura-2AM. We first determined the IC50 of AII which desensitizes the increase in [Ca++]i of 44.7±5.4% over basal levels. Previous exposure to AII 10-10, 10-9, 10-8 and 10-7M reduced spike increase to 38.2±4.2%, 15.1±2.3%, 4.2±1.3% and 1.8±1.5%. Calculated IC50 was 6.9x10-9M, which is similar to Kd values for the AII receptor in hypophysis. We next determined the time needed for cells to recover a complete response to AII after an homologous desensitization with it. Initial stimulus (10-6M AII) was applied for less than 5 min and washed. Cells were then challenged with 10-7M AII 15, 30, 60, 120 or 240 min thereafter. We observed a gradual recovery of [Ca++]i response to AII. At 15 min there was only a 33.0±2.5% of a maximum response, at 30 min 49.3±5.4%, and at 60, 120 and 240 min response was 51.0±7.3, 58.9±8.4 and 79.4±9.5% of undesensitized one, respectively. A full response was not evident even 4 hs alter first stimulus had been washed. We therefore tested if depletion of intracellular calcium stores could account for attenuated response by challenging desensitized cells at 60 min with 1uM ionomycin. We found that [Ca++]i increases were not different, indicating that an additional mechanism to calcium depletion participated in the phenomenom of desensitization described.