Maturation of rat cerebellar Purkinje cells reveals an atypical Ca2+ channel current that is inhibited by omega-agatoxin IVA and the dihydropyridine (-)-(S)-Bay K8644.
To determine if the properties of Ca2+ channels in cerebellar Purkinje cells change during postnatal development, we recorded Ca2+ channel currents from Purkinje cells in cerebellar slices of mature (postnatal days (P) 40-50) and immature (P13-20) rats. We found that at P40-50, the somatic Ca2+ channel current was inhibited by omega-agatoxin IVA at concentrations selective for P-type Ca2+ channels (approximately 85%; IC50, <1 nM) and by the dihydropyridine (-)-(S)-Bay K8644 (approximately 70%; IC50, approximately 40 nM). (-)-(S)-Bay K8644 is known to activate L-type Ca2+ channels, but the decrease in current was not secondary to the activation of L-type channels because inhibition by (-)-(S)-Bay K8644 persisted in the presence of the L-type channel blocker (R,S)-nimodipine. By contrast, at P13-20, the current was inhibited by omega-agatoxin IVA (approximately 86%; IC50, approximately 1 nM) and a minor component was inhibited by (R,S)-nimodipine (approximately 8%). The dihydropyridine (-)-(S)-Bay K8644 had no clear effect when applied alone, but in the presence of (R,S)-nimodipine it reduced the current (approximately 40%), suggesting that activation of L-type channels by (-)-(S)-Bay K8644 masks its inhibition of non-L-type channels. Our findings indicate that Purkinje neurons express a previously unrecognized type of Ca2+ channel that is inhibited by omega-agatoxin IVA, like prototypical P-type channels, and by (-)-(S)-Bay K8644, unlike classical P-type or L-type channels. During maturation, there is a decrease in the size of the L-type current and an increase in the size of the atypical Ca2+ channel current. These changes may contribute to the maturation of the electrical properties of Purkinje cells.
Tringham
Elizabeth W
EW
Department of Pharmacology, University of Bristol, University Walk, Bristol BS8 1TD, UK.
Payne
C Elizabeth
CE
Dupere
Jonathan R B
JR
Usowicz
Maria M
MM
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology*; D002525:Cerebellar Cortex / Q000254:growth & development; D004095:Dihydropyridines / Q000494:pharmacology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D011689:Purkinje Cells / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D020867:omega-Agatoxin IVA / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D004095:Dihydropyridines; D020867:omega-Agatoxin IVA; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine