Spontaneous intracellular calcium oscillations in cortical astrocytes from a patient with intractable childhood epilepsy (Rasmussen's Encephalitis)

Abstract

Many studies have demonstrated that astrocytes respond with fluctuations in intracellular calcium concentration ([Ca2+]i) and membrane potential following the application of a number of ligands. Moreover, calcium (Ca2+) waves that spread through astrocytic syncitia have been described in numerous reports. We had the rare opportunity to study Ca2+ responses in astrocytes obtained from a patient diagnosed with Rasmussen's encephalitis, a rare form of intractable epilepsy. Using the ratiometric fluorescent indicator fura-2, we observed large spontaneous [Ca2+]i oscillations. The mean time between initial rise in [Ca2+]i and the return to baseline was 5.1 +/- 0.19 minutes (SEM; n = 201) and [Ca2+]i increased to a mean level of 271 +/- 8 nM (SEM; n = 201) from a baseline of 136 +/- 6 nM (SEM; n = 201). Removal of Ca2+ from the perfusion solution combined with the addition of the Ca2+ chelator EGTA (2 mM) completely but reversibly eliminated all oscillations suggesting the fluctuations were dependent on Ca2+ flux across the membrane. The percentage of cells undergoing spontaneous changes in [Ca2+]i decreased over time in culture. At 10-11 days postsurgery, approximately 70% of the cells were exhibiting this behavior, and by day 23 transients were no longer observed. We did not observe comparable spontaneous [Ca2+]i oscillations in rat cortical astrocytes. The potential that the spontaneous [Ca2+]i oscillations observed may be a unique feature of epileptic tissues is discussed.