Erschienen in:
The Journal of Neuroscience, 23 (2003) 14, Seite 6041-6049
Sprache:
Englisch
DOI:
10.1523/jneurosci.23-14-06041.2003
ISSN:
0270-6474;
1529-2401
Entstehung:
Anmerkungen:
Beschreibung:
The neuronal L-type calcium channels (LTCCs) Cav1.2α1 and Cav1.3α1 are functionally distinct. Cav1.3α1 activates at lower voltages and inactivates more slowly than Cav1.2α1, making it suitable to support sustained L-type Ca2+inward currents (ICa,L) and serve in pacemaker functions. We compared the biophysical and pharmacological properties of human retinal Cav1.4α1 using the whole-cell patch-clamp technique after heterologous expression in tsA-201 cells with other L-type α1 subunits. Cav1.4α1-mediated inward Ba2+currents (IBa) required the coexpression of α2δ1 and β3 or β2a subunits and were detected in a lower proportion of transfected cells than Cav1.3α1.IBaactivated at more negative voltages (5% activation threshold; -39mV; 15 mmBa2+) than Cav1.2α1 and slightly more positive than Cav1.3α1. Voltage-dependent inactivation ofIBawas slower than for Cav1.2α1 and Cav1.3α1(∼50% inactivation after 5 sec; α2δ1 + β3 coexpression). Inactivation was not increased with Ca2+as the charge carrier, indicating the absence of Ca2+-dependent inactivation. Cav1.4α1 exhibited voltage-dependent, G-protein-independent facilitation by strong depolarizing pulses. The dihydropyridine (DHP)-antagonist isradipine blocked Cav1.4α1 with ∼15-fold lower sensitivity than Cav1.2α1 and in a voltage-dependent manner. Strong stimulation by the DHP BayK 8644 was found despite the substitution of an otherwise L-type channel-specific tyrosine residue in position 1414 (repeat IVS6) by a phenylalanine. Cav1.4α1 + α2δ1 + β channel complexes can form LTCCs with intermediate DHP antagonist sensitivity lacking Ca2+-dependent inactivation. Their biophysical properties should enable them to contribute to sustainedICa,Lat negative potentials, such as required for tonic neurotransmitter release in sensory cells and plateau potentials in spiking neurons.