Voltage-gated calcium channels inPleurodelesoocytes: classification, modulation and functional roles

Abstract

SummaryIn unfertilisedPleurodelesoocytes, two distinct types of high voltage-activated Ca2+channels are expressed: a slowly inactivating Ca2+channel and a transient one. The first is dihydropyridine-sensitive and is referred to as the L-type Ca2+channel. The transient channel is highly sensitive to Ni2+. Phosphorylation through protein kinases G and A facilitates and inhibits the L-type Ca2+channel respectively. The transient type channel is insensitive to stimulation by protein kinases (A and G). The functional expression of L-type and transient Ca2+channels is modulated by the two maturation seasons. The transient Ca2+currents are only observed during the resting season, while the L-type current is observed either alone during the breeding season or in association with the transient current during the resting season. Moreover, the current density of the L-type Ca2+channel is much greater during the breeding season than the resting season. Thus, the wide distribution of L-type Ca2+channels inPleurodelesoocytes during the two seasons suggests that the roles of these channels may be important in the regulation of the maturation process.