Calcium signalling in cortical and thalamic neurons of rats with streptozotocin-induced diabetes

Intracellular Ca2+ transients were measured with the use of a Ca2+-sensitive fluorescent indicator, fura-2, in neocortical and thalamic neurons in brain slices from control rats and rats with uncompensated streptozotocin-induced diabetes. The transients were evoked by high-potassium (50 mM)-induced membrane depolarization. The amplitude of depolarization-induced Ca2+ transients demonstrated a tendency to increase under diabetic conditions, beeing more expressed in cortical neurons compared with thalamic ones. The transients in cortical neurons from diabetic animals became also more susceptible to the blocking action of nifedipine (100μM) and less sensitive to Ni2+ (50μM), indicating that diabetic changes affect mostly Ca2+ transients triggered by high-voltage activated (L-type) calcium channels. The duration of a statistically significant increase was observed in the residual elevation of intracellular Ca2+ changes. However, a statistically significant increase was observed in the residual elevation of intracellular Ca2+ measured 60 sec after termination of membrane depolarization in both cortical and thalamic neurons, indicating alterations in the mechanisms that restore the resting level of Ca2+ in the cytosol. It is concluded that uncomensated insulin-dependent diabetes, which according to earlier data substantially alters calcium signalling in primary sensory neurons, also affects such signalling in the neurons of higher brain structures including the thalamus and cortex.