Store-depletion and hyperforin activate distinct types of Ca2+-conducting channels in cortical neurons

Cortical neurons embryos (E13) from murine brain have a wide diversity of plasma membrane Ca2+-conducting channels. For instance, they express several types of transient receptor potential channels of C-type (TRPC) and hyperforin, a potent TRPC6-channel activator, controls the activity of TRPC6-like channels. In addition, E13 cortical neurons possess plasma membrane channels activated in response to the depletion of internal Ca2+ pools. Since some TRPC channels seem to be involved in the activity of store-depletion-activated channels, we investigated whether hyperforin and the depletion of the Ca2+ stores control similar or distinct Ca2+ routes. Calcium imaging experiments performed with the fluorescent Ca2+ indicator Fluo-4 showed that the TRPC3 channel blocker Pyr3 potently inhibits with an IC50 of 0.5 μM the entry of Ca2+ triggered in response to the thapsigargin-dependent depletion of the Ca2+ stores. On the other hand, Pyr3 does not block the hyperforin-sensitive Ca2+ entry. In contrast to the hyperforin responses, the Ca2+ entry through the store-depletion-activated channels is down-regulated by the competitive tyrosine kinase inhibitors genistein and PP2. In addition, the immunosuppressant FK506, known to modulate several classes of Ca2+-conducting channels, strongly attenuates the entry of Ca2+ through the store-depletion-activated channels, leaving the hyperforin-sensitive responses unaffected. Hence, the Zn2+ chelator TPEN markedly attenuated the hyperforin-sensitive responses without modifying the thapsigargin-dependent Ca2+ signals. Pyr3-insensitive channels are key components of the hyperforin-sensitive channels, whereas the thapsigargin-dependent depletion of the Ca2+ stores of the endoplasmic reticulum activates Pyr3-sensitive channels. Altogether, these data support the notion that hyperforin and the depletion of the Ca2+ pools control distinct plasma membrane Ca2+-conducting channels. This report further illustrates that, at the beginning of the corticogenesis, immature cortical neurons express diverse functional Ca2+ channels.