Developmental changes in purinergic calcium signalling in rat neocortical neurones

Abstract

The changes in cytoplasm free calcium concentration ([Ca 2+] i transients) were measured in Fura-2/AM loaded pyramidal neurones of sensorimotor cortex in acutely prepared slices isolated from 14 days (P14) and 30 (P30) days old rats. Ni 2+ (50 μM) diminished the [Ca 2+] i transients evoked by 50 mM KCl bath application by 47%±8% in neurones of the P14 group and only by 15%±6% in those of P30 group ( P<0.002). Nifedipine and verapamil in concentration 100 μM reduced the calcium transients amplitude triggered by depolarization to about the same extent in both groups of neurons—on average by 50% and 35%, respectively. The amplitude of [Ca 2+] i transients induced by application of 100 μM ATP reached 103±6 nM in P14 neurones and 72±8 nM in the P30 ones. The ATP-[Ca 2+] i induced transient could be evoked in Ca 2+-free external solution, indicating the presence of metabotropic (P2 y) purinoreceptors. Almost all (90%) P14 neurones were endowed with such receptors. At the same time only 1/3 of the tested ( n=42) P30 neurones presented responses to ATP applications in Ca 2+-free solution. The share of ionotropic (P2 x) purinoreceptors in generation of calcium signal was the same in both groups of neurons. No caffeine-induced Ca 2+-release has been observed in the P14 neurons. To the contrary, in 28 cells from 42 investigated neurones of the P30 group application of 40 mM caffeine for 10 s induced considerable [Ca 2+] i transients, which did not disappear in calcium-free solution. A conclusion is made about substantial changes in the expression of Ca 2+-handling mechanisms which are occurring in neocortical neurones at the third–fourth week of postnatal development.