Development of Ca2+-channel and BK-channel expression in embryos and larvae of Xenopus laevis.
The patterns and density of channels expressed in neurons critically determine their electrical properties. We have examined developmental regulation of Ca2+-channel expression during the maturation of the spinal motor circuits in Xenopus as it develops from an embryo to a larva. In embryonic neurons approximately 60% of the current is carried by N-type channels, 8% by l-type channels and the remainder by an unidentified channel. As the embryo matures, omega-agatoxin-sensitive P/Q channels are gradually expressed and replace the unidentified HVA channel such that at stage 42 approximately 25% of the current is carried by P/Q channels. We have used fluorescent labelling of selective channel toxins to directly observe the distribution of P/Q, N and BK channels. The P/Q channel distribution was most prevalent on the cell surface proximal to the areas of the soma where processes emerge. Both N and BK channels were distributed throughout the soma but still exhibited concentration around the areas adjacent to the emergence of processes from the soma. The patterns of fluorescence labelling during development mirrored the development of the respective ionic currents. Both N and P/Q channels contribute roughly equally to activation of the BK current, suggesting that overlap in the distribution of the N, P/Q and BK channels is important in their functional interdependence. The newly expressed P/Q channels play a role in spike initiation and repetitive firing in larval spinal neurons and contribute to burst generation during swimming in the larva.
Jiménez-González
Cristina
C
Department of Biological Sciences, University of Warwick, Coventry, CV4 7AL, UK.
McLaren
Gerald J
GJ
Dale
Nicholas
N
D000375:Aging; D000818:Animals; D001710:Biotin / Q000378:metabolism; D002121:Calcium Channel Blockers; D015220:Calcium Channels / Q000378:metabolism*; D002452:Cell Count; D004347:Drug Interactions; D004625:Embryo, Nonmammalian / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000378:metabolism; D051036:Large-Conductance Calcium-Activated Potassium Channels; D007814:Larva / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D013997:Time Factors; D014981:Xenopus; D014982:Xenopus laevis; D020867:omega-Agatoxin IVA / Q000494:pharmacology; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005456:Fluorescent Dyes; D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D020867:omega-Agatoxin IVA; D001710:Biotin; D020866:omega-Conotoxin GVIA